ORCID Profile
0000-0001-5254-0728
Current Organisations
Harvard University
,
Queensland University of Technology
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Other Physical Sciences | Medical Physics | Therapies And Therapeutic Technology | Medical Physics | Physical Sciences not elsewhere classified | Radiotherapy And Nuclear Medicine
Expanding Knowledge in the Physical Sciences | Cancer and Related Disorders | Cancer and related disorders |
Publisher: Elsevier BV
Date: 12-2013
DOI: 10.1016/J.RADONC.2013.10.002
Abstract: The goal of this work was to set out a methodology for measuring and reporting small field relative output and to assess the application of published correction factors across a population of linear accelerators. Measurements were made at 6 MV on five Varian iX accelerators using two PTW T60017 unshielded diodes. Relative output readings and profile measurements were made for nominal square field sizes of side 0.5 to 1.0 cm. The actual in-plane (A) and cross-plane (B) field widths were taken to be the FWHM at the 50% isodose level. An effective field size, defined as √FS eff=A · B, was calculated and is presented as a field size metric. FSeff was used to linearly interpolate between published Monte Carlo (MC) calculated [Formula in text] values to correct for the diode over-response in small fields. The relative output data reported as a function of the nominal field size were different across the accelerator population by up to nearly 10%. However, using the effective field size for reporting showed that the actual output ratios were consistent across the accelerator population to within the experimental uncertainty of ± 1.0%. Correcting the measured relative output using [Formula in text] at both the nominal and effective field sizes produce output factors that were not identical but differ by much less than the reported experimental and/or MC statistical uncertainties. In general, the proposed methodology removes much of the ambiguity in reporting and interpreting small field dosimetric quantities and facilitates a clear dosimetric comparison across a population of linacs.
Publisher: IOP Publishing
Date: 05-2017
Publisher: IOP Publishing
Date: 22-07-2014
Publisher: IOP Publishing
Date: 05-2017
Publisher: Wiley
Date: 07-2014
Publisher: CRC Press
Date: 28-03-2021
Publisher: Wiley
Date: 09-2014
DOI: 10.1002/JMRS.74
Publisher: Elsevier BV
Date: 12-2011
Publisher: IOP Publishing
Date: 26-06-2013
Publisher: Springer Science and Business Media LLC
Date: 03-2013
Publisher: Springer Berlin Heidelberg
Date: 2013
Publisher: Springer Science and Business Media LLC
Date: 03-2014
Publisher: Springer Berlin Heidelberg
Date: 2013
Publisher: Springer Science and Business Media LLC
Date: 12-05-2022
DOI: 10.1007/S13246-022-01131-5
Abstract: An increase in radiotherapy-induced secondary malignancies has led to recent developments in analytical modelling of out-of-field dose. These models must be validated against measurements, but currently available datasets are outdated or limited in scope. This study aimed to address these shortcomings by producing a large dataset of out-of-field dose profiles measured with modern equipment. A novel method was developed with the intention of allowing physicists in all clinics to perform these measurements themselves using commonly available dosimetry equipment. A standard 3D scanning water tank was used to collect 36 extended profiles. Each profile was measured in two sections, with the inner section measured with the beam directly incident on the tank, and the outer section with the beam incident on a water-equivalent phantom abutted next to the tank. The two sections were then stitched using a novel feature-matching approach. The profiles were compared against linac commissioning data and manually inspected for discontinuities in the overlap region. The dataset is presented as a publicly accessible comma separated variable file containing off-axis ratios at a range of off-axis distances. This dataset may be applied to the development and validation of analytical models of out-of-field dose. Additionally, it may be used to inform dose estimates to radiosensitive implants and anatomy. Physicists are encouraged to perform these out-of-field measurements in their own clinics and share their results with the community.
Publisher: Elsevier BV
Date: 09-2018
DOI: 10.1016/J.EJMP.2018.08.003
Abstract: This study investigated planned MLC distribution and treatment region specific plan parameters to recommend optimal delivery parameters based on statistical process techniques. A cohort of 28 head and neck, 19 pelvic and 23 brain pre-treatment plans were delivered on a helical tomotherapy system using 2.5 cm field width. Parameters such as gantry period, leaf open time (LOT), actual modulation factor, LOT sonogram, treatment duration and couch travel were investigated to derive optimal range for plans that passed acceptable delivery quality assurance. The results were compared against vendor recommendations and previous publications. No correlation was observed between vendor recommended gantry period and percentage of minimum leaf open times. The range of gantry period (min-max) observed was 16-21 s for head and neck, 15-22 s for pelvis and 13-18 s for brain plans respectively. It was also noted that the highest percentage (average (X-) ± SD) of leaf open times for a minimum time of 100 ms was seen for brain plans (53.9 ± 9.2%) compared to its corresponding head and neck (34.5 ± 4.2%) and pelvic (32.0 ± 9.4%) plans respectively. We have proposed that treatment site specific delivery parameters be used during planning that are based on the treatment centre and have detailed recommendations and limitations for the studied cohort. This may enable to improve efficiency of treatment deliveries by reducing inaccuracies in MLC distribution.
Publisher: Elsevier BV
Date: 07-2006
Publisher: Springer Science and Business Media LLC
Date: 08-03-2014
DOI: 10.1007/S13246-014-0258-9
Abstract: In order to increase the accuracy of patient positioning for complex radiotherapy treatments various 3D imaging techniques have been developed. MegaVoltage Cone Beam CT (MVCBCT) can utilise existing hardware to implement a 3D imaging modality to aid patient positioning. MVCBCT has been investigated using an unmodified Elekta Precise Linac and iView amorphous silicon electronic portal imaging device (EPID). Two methods of delivery and acquisition have been investigated for imaging an anthropomorphic head phantom and quality assurance phantom. Phantom projections were successfully acquired and CT datasets reconstructed using both acquisition methods. Bone, tissue and air were clearly resolvable in both phantoms even with low dose (22 MU) scans. The feasibility of MVCBCT was investigated using a standard linac, amorphous silicon EPID and a combination of a free open source reconstruction toolkit as well as custom in-house software written in Matlab. The resultant image quality has been assessed and presented. Although bone, tissue and air were resolvable in all scans, artifacts are present and scan doses are increased when compared with standard portal imaging. The feasibility of MVCBCT with unmodified Elekta Precise Linac and EPID has been considered as well as the identification of possible areas for future development in artifact correction techniques to further improve image quality.
Publisher: IOP Publishing
Date: 28-10-2010
Publisher: IOP Publishing
Date: 12-01-2015
Publisher: IOP Publishing
Date: 12-01-2015
Publisher: Elsevier BV
Date: 05-2015
DOI: 10.1016/J.EJMP.2015.01.015
Abstract: This study investigates the effects of temporary tissue expanders (TTEs) on the dose distributions in breast cancer radiotherapy treatments under a variety of conditions. Using EBT2 radiochromic film, both electron and photon beam dose distribution measurements were made for different phantoms, and beam geometries. This was done to establish a more comprehensive understanding of the implant's perturbation effects under a wider variety of conditions. The magnetic disk present in a tissue expander causes a dose reduction of approximately 20% in a photon tangent treatment and 56% in electron boost fields immediately downstream of the implant. The effects of the silicon elastomer are also much more apparent in an electron beam than a photon beam. Evidently, each component of the TTE attenuates the radiation beam to different degrees. This study has demonstrated that the accuracy of photon and electron treatments of post-mastectomy patients is influenced by the presence of a tissue expander for various beam orientations. The impact of TTEs on dose distributions establishes the importance of an accurately modelled high-density implant in the treatment planning system for post-mastectomy patients.
Publisher: Wiley
Date: 19-07-2016
DOI: 10.1118/1.4958679
Abstract: An experimental extrapolation technique is presented, which can be used to determine the relative output factors for very small x-ray fields using the Gafchromic EBT3 film. Relative output factors were measured for the Brainlab SRS cones ranging in diameters from 4 to 30 mm(2) on a Novalis Trilogy linear accelerator with 6 MV SRS x-rays. The relative output factor was determined from an experimental reducing circular region of interest (ROI) extrapolation technique developed to remove the effects of volume averaging. This was achieved by scanning the EBT3 film measurements with a high scanning resolution of 1200 dpi. From the high resolution scans, the size of the circular regions of interest was varied to produce a plot of relative output factors versus area of analysis. The plot was then extrapolated to zero to determine the relative output factor corresponding to zero volume. Results have shown that for a 4 mm field size, the extrapolated relative output factor was measured as a value of 0.651 ± 0.018 as compared to 0.639 ± 0.019 and 0.633 ± 0.021 for 0.5 and 1.0 mm diameter of analysis values, respectively. This showed a change in the relative output factors of 1.8% and 2.8% at these comparative regions of interest sizes. In comparison, the 25 mm cone had negligible differences in the measured output factor between zero extrapolation, 0.5 and 1.0 mm diameter ROIs, respectively. This work shows that for very small fields such as 4.0 mm cone sizes, a measureable difference can be seen in the relative output factor based on the circular ROI and the size of the area of analysis using radiochromic film dosimetry. The authors recommend to scan the Gafchromic EBT3 film at a resolution of 1200 dpi for cone sizes less than 7.5 mm and to utilize an extrapolation technique for the output factor measurements of very small field dosimetry.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2012
Publisher: Springer Science and Business Media LLC
Date: 16-06-2011
DOI: 10.1007/S13246-011-0081-5
Abstract: In this feasibility study an organic plastic scintillator is calibrated against ionisation chamber measurements and then embedded in a polymer gel dosimeter to obtain a quasi-4D radiation detector. This hybrid dosimeter was irradiated with megavoltage x-rays from a linear accelerator, with temporal measurements of the dose rate being acquired by the scintillator and spatial measurements acquired with the gel dosimeter. The detectors employed in this study are radiologically equivalent and we show that neither detector perturbs the intensity of the radiation field of the other. By employing these detectors in concert, spatial and temporal variations in the radiation intensity can now be detected and gel dosimeters can be calibrated for absolute dose from a single irradiation.
Publisher: IOP Publishing
Date: 26-06-2013
Publisher: Springer Science and Business Media LLC
Date: 22-05-2015
DOI: 10.1007/S13246-015-0348-3
Abstract: A software-based environment was developed to provide practical training in medical radiation principles and safety. The Virtual Radiation Laboratory application allowed students to conduct virtual experiments using simulated diagnostic and radiotherapy X-ray generators. The experiments were designed to teach students about the inverse square law, half value layer and radiation protection measures and utilised genuine clinical and experimental data. Evaluation of the application was conducted in order to ascertain the impact of the software on students' understanding, satisfaction and collaborative learning skills and also to determine potential further improvements to the software and guidelines for its continued use. Feedback was gathered via an anonymous online survey consisting of a mixture of Likert-style questions and short answer open questions. Student feedback was highly positive with 80 % of students reporting increased understanding of radiation protection principles. Furthermore 72 % enjoyed using the software and 87 % of students felt that the project facilitated collaboration within small groups. The main themes arising in the qualitative feedback comments related to efficiency and effectiveness of teaching, safety of environment, collaboration and realism. Staff and students both report gains in efficiency and effectiveness associated with the virtual experiments. In addition students particularly value the visualisation of "invisible" physical principles and increased opportunity for experimentation and collaborative problem-based learning. Similar ventures will benefit from adopting an approach that allows for in idual experimentation while visualizing challenging concepts.
Publisher: IOP Publishing
Date: 26-06-2013
Publisher: Springer Science and Business Media LLC
Date: 23-05-2023
DOI: 10.1007/S13246-023-01270-3
Abstract: Gamma evaluation is currently the most widely used dose comparison method for patient specific quality assurance (PSQA). However, existing methods for normalising the dose difference, using either the dose at the global maximum dose point or at each local point, can respectively lead to under- and over-sensitivity to dose differences in organ-at-risk structures. This may be of concern for plan evaluation from clinical perspectives. This study has explored and proposed a new method called structural gamma, which takes structural dose tolerances into consideration while performing gamma analysis for PSQA. As a demonstration of the structural gamma method, a total of 78 retrospective plans on four treatment sites were re-calculated on an in-house Monte Carlo system and compared with doses calculated from the treatment planning system. Structural gamma evaluations were performed using both QUANTEC dose tolerances and radiation oncologist specified dose tolerances, then compared with conventional global and local gamma evaluations. Results demonstrated that structural gamma evaluation is especially sensitive to errors in structures with restrictive dose constraints. The structural gamma map provides both geometric and dosimetric information on PSQA results, allowing straightforward clinical interpretation. The proposed structure-based gamma method accounts for dose tolerances for specific anatomical structures. This method can provide a clinically useful method to assess and communicate PSQA results, offering radiation oncologists a more intuitive way of examining agreement in surrounding critical normal structures.
Publisher: Elsevier BV
Date: 02-2014
Publisher: IEEE
Date: 2007
Publisher: Elsevier BV
Date: 2021
Publisher: IOP Publishing
Date: 06-06-2007
DOI: 10.1088/0031-9155/52/13/022
Abstract: There are a number of gel dosimeter calibration methods in contemporary usage. The present study is a detailed Monte Carlo investigation into the accuracy of several calibration techniques. Results show that for most arrangements the dose to gel accurately reflects the dose to water, with the most accurate method involving the use of a large diameter flask of gel into which multiple small fields of varying dose are directed. The least accurate method was found to be that of a long test tube in a water phantom, coaxial with the beam. The large flask method is also the most straightforward and least likely to introduce errors during the set-up, though, to its detriment, the volume of gel required is much more than other methods.
Publisher: Springer Science and Business Media LLC
Date: 04-2011
Publisher: IOP Publishing
Date: 12-01-2015
Publisher: IOP Publishing
Date: 26-06-2013
Publisher: IOP Publishing
Date: 09-05-2012
DOI: 10.1088/0031-9155/57/11/3359
Abstract: The quality assurance of stereotactic radiotherapy and radiosurgery treatments requires the use of small-field dose measurements that can be experimentally challenging. This study used Monte Carlo simulations to establish that PAGAT dosimetry gel can be used to provide accurate, high-resolution, three-dimensional dose measurements of stereotactic radiotherapy fields. A small cylindrical container (4 cm height, 4.2 cm diameter) was filled with PAGAT gel, placed in the parietal region inside a CIRS head phantom and irradiated with a 12-field stereotactic radiotherapy plan. The resulting three-dimensional dose measurement was read out using an optical CT scanner and compared with the treatment planning prediction of the dose delivered to the gel during the treatment. A BEAMnrc/DOSXYZnrc simulation of this treatment was completed, to provide a standard against which the accuracy of the gel measurement could be gauged. The three-dimensional dose distributions obtained from Monte Carlo and from the gel measurement were found to be in better agreement with each other than with the dose distribution provided by the treatment planning system's pencil beam calculation. Both sets of data showed close agreement with the treatment planning system's dose distribution through the centre of the irradiated volume and substantial disagreement with the treatment planning system at the penumbrae. The Monte Carlo calculations and gel measurements both indicated that the treated volume was up to 3 mm narrower, with steeper penumbrae and more variable out-of-field dose, than predicted by the treatment planning system. The Monte Carlo simulations allowed the accuracy of the PAGAT gel dosimeter to be verified in this case, allowing PAGAT gel to be utilized in the measurement of dose from stereotactic and other radiotherapy treatments, with greater confidence in the future.
Publisher: Springer Science and Business Media LLC
Date: 20-11-2019
DOI: 10.1007/S13246-018-0715-Y
Abstract: This study aimed to develop a method for performing accurate, high-resolution, three-dimensional (3D) Fricke gel dosimetry measurements of high dose rate (HDR) brachytherapy dose distributions using optical computed tomography (CT). A multi-needle brachytherapy gel phantom was purpose-built to contain four stainless-steel brachytherapy needles and a s le of Fricke Xylenol gel. A Paris-style HDR brachytherapy treatment was planned and delivered to the gel, which was then read out using a novel optical CT scanning method all the brachytherapy needles were removed prior to scanning and replaced with a refractive index matched fluid. The removal of the stainless-steel needles during pre- and post-irradiation scanning minimised the potential for artefacts caused by missing ray-sum data. Results showed good agreement between measured and calculated doses (within 1%) at all positions greater than 0.1 cm from each needle. This study demonstrated that 3D Fricke gel phantoms may be valuable tools in verifying HDR brachytherapy treatments. The phantom construction and optical CT scanning method proposed in this work has the potential to enable routine quality assurance measurements of complex HDR brachytherapy treatment deliveries via accurate and detailed three-dimensional dose measurements.
Publisher: IOP Publishing
Date: 12-01-2023
Publisher: Wiley
Date: 23-09-2016
DOI: 10.1118/1.4963210
Abstract: The dose-response of radiochromic film has been shown to be dependent on the quality of the incident radiation, particularly at low energies. Difficulty therefore arises when a calibration is required for radiation of uncertain energy. This study investigates the ability of a recently published calibration method [see M. T oni et al., "A new form of the calibration curve in radiochromic dosimetry. Properties and results," Med. Phys. 43, 4435-4446 (2016)] to reduce the energy-dependence of radiochromic film. This allows for corrections to be applied that may improve the accuracy and precision of measurements taken in beams of uncertain energy or where the beam quality is known but calibration doses cannot be delivered. Gafchromic EBT3 film was irradiated with a range of superficial, orthovoltage, and high-energy photon beams. Calibrations were then applied using a typical net optical density approach and compared with the T oni et al. method that instead defines the response as a ratio of two net optical densities. To quantify the energy dependence, the response at each beam quality and dose was then normalized to the response at a preselected reference quality. This resulted in a relative measure that could be used to correct the calibration curve at the reference beam quality to any other quality of interest. The T oni et al. calibration method resulted in substantially less energy dependence compared to the standard net optical density approach, without compromising the calibration fit. The maximum deviation from the reference beam calibration curve was 7% across the range of energies and doses analyzed, reducing to <3% for doses greater than 200 cGy. However, the ability of the calibration curve to fit the data deteriorated as the curve was refitted with measurements at higher doses than those originally studied. The T oni et al. calibration method, based on the ratio of two net optical densities, considerably reduces the energy dependence of Gafchromic EBT3 film. Manipulating the calibration data in the fashion presented in this study allows for a readily available calibration curve to be corrected to represent calibration curves at different energies. This may be useful when a calibration is desired for a beam where the delivery of a set of calibration doses is problematic, such as with out-of-field measurements, radioactive sources, and imaging applications.
Publisher: Elsevier BV
Date: 2019
DOI: 10.1016/J.MEDDOS.2018.11.002
Abstract: Due to large doses per fraction, stereotactic ablative radiotherapy of lung or spine can lead to skin tissue toxicity, the amount of which depends on a variety of factors such as target location, beam geometry, and immobilization. The effect of arc length on spreading out entrance and exit doses and the corresponding predictions of skin reactions has not yet been studied for stereotactic body radiotherapy volumetric modulated arc therapy (VMAT) treatments. 58 clinically relevant VMAT stereotactic body radiotherapy spine and lung plans were created for an anthropomorphic phantom utilizing a range of target locations, beam geometries and arc lengths. Skin dose was assessed by considering the National Cancer Institute skin reaction grades adjusted for 3 fraction treatments. While the skin volumes predicted to exhibit low grade reactions decreased with arc length, high grade reactions were found to increase at smaller arcs as well as at full arcs where a superposition of entrance and exit doses would occur. It is possible for skin dose to be effectively optimized by choice of arc length (within clinically relevant boundaries) and thus minimize the skin reaction. High skin doses are often attributed to effects arising from the distance between the planning target volume and patient surface but this study has demonstrated that VMAT arc length is of equal importance. Understanding this relationship will assist in minimizing skin reactions through modification of plan parameters and will provide clinicians more information for patient selection.
Publisher: Elsevier BV
Date: 10-2021
Publisher: Springer Science and Business Media LLC
Date: 27-10-2016
DOI: 10.1007/S13246-016-0493-3
Abstract: This study evaluated the accuracy of image thresholding in the reconstruction of catheters in brachytherapy treatment planning systems. Six test cases including four planar catheter configurations, an interstitial prostate and an intracavitary treatment plan were made use of in this study. The four planar CT scanned catheter arrangements included catheters placed approximately 1, 0.5 cm apart, catheters closely arranged in a plan (<0.5 cm apart) and a loop arrangement. The intracavitary plan consisted of catheters arranged inside a mould configuration. All reconstruction methods were based on tracking wire markers placed inside the plastic catheters. Each of these catheter arrangements was reconstructed using an existing window adjustment technique (manual reconstruction) in the treatment planning system followed by a CT-based automated thresholding technique available in the same planning system. A corresponding reconstructed catheter was created using a segmented catheter structure using image thresholding from another planning system within the same department. Co-ordinates from all the reconstructed catheters were compared against each other to assess the geometric shift between manual and threshold based reconstruction on each transaxial image using in-house software and the maximum variations were recorded for assessment. It was observed in general that automated thresholding technique could assist in catheter reconstruction for catheters which are greater than 0.5 cm apart. The segmented thresholding method reported smaller variations when compared to the manual reconstruction using window adjustment technique. Automated reconstruction saves time in the brachytherapy planning, however it was noted that it is not feasible for closely spaced catheters. Segmented catheter reconstruction although time consuming, did provide a better alternative in most cases.
Publisher: Springer Science and Business Media LLC
Date: 30-08-2016
DOI: 10.1007/S13246-016-0478-2
Abstract: There are often differences in a publication's citation count, depending on the database accessed. Here, aspects of citation counts for medical physics and biomedical engineering papers are studied using papers published in the journal Australasian physical and engineering sciences in medicine. Comparison is made between the Web of Science, Scopus, and Google Scholar. Papers are categorised into subject matter, and citation trends are examined. It is shown that review papers as a group tend to receive more citations on average however the highest cited in idual papers are more likely to be research papers.
Publisher: Hindawi Limited
Date: 04-07-2020
DOI: 10.1111/TBED.13693
Publisher: Springer Science and Business Media LLC
Date: 19-03-2011
DOI: 10.1007/S13246-011-0060-X
Abstract: The purpose of this work is to validate and automate the use of DYNJAWS a new component module (CM) in the BEAMnrc Monte Carlo (MC) user code. The DYNJAWS CM simulates dynamic wedges and can be used in three modes dynamic, step-and-shoot and static. The step-and-shoot and dynamic modes require an additional input file defining the positions of the jaw that constitutes the dynamic wedge, at regular intervals during its motion. A method for automating the generation of the input file is presented which will allow for the more efficient use of the DYNJAWS CM. Wedged profiles have been measured and simulated for 6 and 10 MV photons at three field sizes (5 cm × 5 cm, 10 cm × 10 cm and 20 cm × 20 cm), four wedge angles (15°, 30°, 45° and 60°), at d (max) and at 10 cm depth. Results of this study show agreement between the measured and the MC profiles to within 3% of absolute dose or 3 mm distance to agreement for all wedge angles at both energies and depths. The gamma analysis suggests that dynamic mode is more accurate than the step-and-shoot mode. The DYNJAWS CM is an important addition to the BEAMnrc code and will enable the MC verification of patient treatments involving dynamic wedges.
Publisher: Elsevier BV
Date: 11-2018
Publisher: Medknow
Date: 2007
Publisher: IOP Publishing
Date: 24-03-2014
Publisher: Springer International Publishing
Date: 2015
Publisher: Wiley
Date: 18-03-2019
DOI: 10.1002/ACM2.12567
Publisher: Wiley
Date: 19-03-2014
DOI: 10.1118/1.4868461
Abstract: This work introduces the concept of very small field size. Output factor (OPF) measurements at these field sizes require extremely careful experimental methodology including the measurement of dosimetric field size at the same time as each OPF measurement. Two quantifiable scientific definitions of the threshold of very small field size are presented. A practical definition was established by quantifying the effect that a 1 mm error in field size or detector position had on OPFs and setting acceptable uncertainties on OPF at 1%. Alternatively, for a theoretical definition of very small field size, the OPFs were separated into additional factors to investigate the specific effects of lateral electronic disequilibrium, photon scatter in the phantom, and source occlusion. The dominant effect was established and formed the basis of a theoretical definition of very small fields. Each factor was obtained using Monte Carlo simulations of a Varian iX linear accelerator for various square field sizes of side length from 4 to 100 mm, using a nominal photon energy of 6 MV. According to the practical definition established in this project, field sizes ≤15 mm were considered to be very small for 6 MV beams for maximal field size uncertainties of 1 mm. If the acceptable uncertainty in the OPF was increased from 1.0% to 2.0%, or field size uncertainties are 0.5 mm, field sizes ≤12 mm were considered to be very small. Lateral electronic disequilibrium in the phantom was the dominant cause of change in OPF at very small field sizes. Thus the theoretical definition of very small field size coincided to the field size at which lateral electronic disequilibrium clearly caused a greater change in OPF than any other effects. This was found to occur at field sizes ≤12 mm. Source occlusion also caused a large change in OPF for field sizes ≤8 mm. Based on the results of this study, field sizes ≤12 mm were considered to be theoretically very small for 6 MV beams. Extremely careful experimental methodology including the measurement of dosimetric field size at the same time as output factor measurement for each field size setting and also very precise detector alignment is required at field sizes at least ≤12 mm and more conservatively≤15 mm for 6 MV beams. These recommendations should be applied in addition to all the usual considerations for small field dosimetry, including careful detector selection.
Publisher: Wiley
Date: 25-02-2016
DOI: 10.1118/1.4942488
Abstract: The aim of this work was to use a multicenter audit of modulated radiotherapy quality assurance (QA) data to provide a practical examination of gamma evaluation criteria and action level selection. The use of the gamma evaluation method for patient‐specific pretreatment QA is widespread, with most commercial solutions implementing the method. Gamma agreement indices were calculated using the criteria 1%/1 mm, 2%/2 mm, 2%/3 mm, 3%/2 mm, 3%/3 mm, and 5%/3 mm for 1265 pretreatment QA measurements, planned at seven treatment centers, using four different treatment planning systems, delivered using three different delivery systems (intensity‐modulated radiation therapy, volumetric‐modulated arc therapy, and helical tomotherapy) and measured using three different dose measurement systems. The sensitivity of each pair of gamma criteria was evaluated relative to the gamma agreement indices calculated using 3%/3 mm. A linear relationship was observed for 2%/2 mm, 2%/3 mm, and 3%/2 mm. This result implies that most beams failing at 3%/3 mm would also fail for those criteria, if the action level was adjusted appropriately. Some borderline plans might be passed or failed depending on the relative priority (tighter tolerance) used for dose difference or distance to agreement evaluation. Dosimeter resolution and treatment modality were found to have a smaller effect on the results of QA measurements than the number of dimensions (2D or 3D) over which the gamma evaluation was calculated. This work provides a method (and a large s le of results) for calculating equivalent action levels for different gamma evaluation criteria. This work constitutes a valuable guide for clinical decision making and a means to compare published gamma evaluation results from studies using different evaluation criteria. More generally, the data provided by this work support the recommendation that gamma criteria that specifically prioritize the property of greatest clinical importance for each treatment modality of anatomical site should be selected when using gamma evaluations for modulated radiotherapy QA. It is therefore suggested that departments using the gamma evaluation as a QA analysis tool should consider the relative importance of dose difference and distance to agreement, when selecting gamma evaluation criteria.
Publisher: Springer Berlin Heidelberg
Date: 2013
Publisher: Springer Science and Business Media LLC
Date: 12-2006
DOI: 10.1007/BF03178400
Publisher: IOP Publishing
Date: 16-10-2019
Abstract: A gel dosimeter has been developed utilising a recently reported system for reducing Fe
Publisher: Springer Science and Business Media LLC
Date: 17-10-2022
Publisher: Wiley
Date: 28-03-2020
DOI: 10.1002/MP.14110
Publisher: Wiley
Date: 11-2014
DOI: 10.1118/1.4895827
Abstract: Small field x-ray beam dosimetry is difficult due to lack of lateral electronic equilibrium, source occlusion, high dose gradients, and detector volume averaging. Currently, there is no single definitive detector recommended for small field dosimetry. The objective of this work was to evaluate the performance of a new commercial synthetic diamond detector, namely, the PTW 60019 microDiamond, for the dosimetry of small x-ray fields as used in stereotactic radiosurgery (SRS). Small field sizes were defined by BrainLAB circular cones (4-30 mm diameter) on a Novalis Trilogy linear accelerator and using the 6 MV SRS x-ray beam mode for all measurements. Percentage depth doses (PDDs) were measured and compared to an IBA SFD and a PTW 60012 E diode. Cross profiles were measured and compared to an IBA SFD diode. Field factors, ΩQclin,Qmsr (fclin,fmsr) , were calculated by Monte Carlo methods using BEAMnrc and correction factors, kQclin,Qmsr (fclin,fmsr) , were derived for the PTW 60019 microDiamond detector. For the small fields of 4-30 mm diameter, there were dose differences in the PDDs of up to 1.5% when compared to an IBA SFD and PTW 60012 E diode detector. For the cross profile measurements the penumbra values varied, depending upon the orientation of the detector. The field factors, ΩQclin,Qmsr (fclin,fmsr) , were calculated for these field diameters at a depth of 1.4 cm in water and they were within 2.7% of published values for a similar linear accelerator. The corrections factors, kQclin,Qmsr (fclin,fmsr) , were derived for the PTW 60019 microDiamond detector. The authors conclude that the new PTW 60019 microDiamond detector is generally suitable for relative dosimetry in small 6 MV SRS beams for a Novalis Trilogy linear equipped with circular cones.
Publisher: Wiley
Date: 19-11-2013
DOI: 10.1002/JMRS.24
Publisher: Elsevier BV
Date: 10-2022
Publisher: Springer Science and Business Media LLC
Date: 09-05-2022
DOI: 10.1007/S13246-022-01126-2
Abstract: The aim of this study is to investigate the effectiveness of dose reducing software (ClarityIQ) on patient and staff dose during fluoroscopically guided cardiac procedures. Dose measurements were collected in a room without dose reducing software (n = 157) and compared with similar procedures performed in two rooms with the software (n = 1141). Procedures included diagnostic coronary angiography, percutaneous coronary intervention, deployment of cardiac closure devices (for occlusion of atrial septal defect, patent foramen ovale, and atrial appendage) and insertion of permanent pacemakers. The dose reducing software was found to be effective in reducing patient and staff dose by approximately 50%. This study has added to the limited literature reporting on the capability of dose reducing software to decrease radiation exposure during the implantation of cardiac closure devices, as well as demonstrating a reduction in dose to the cardiologist and nursing staff. Administrators should ensure timely upgrades to angiographic equipment to safeguard patients and staff against the potentially adverse effects of radiation exposure. Regardless of the use of dose reducing software, the mean occupational dose during closure devices was in descending order scout scrub cardiologist. Scrub nurse dose was found to be higher than the cardiologist during closure devices (0.98/0.26 μSv) and diagnostic coronary angiograms (1.51/0.82 μSv). Nursing staff should be aware that their levels of radiation dose during some cardiac procedures may come close to or even exceed that of the cardiologist.
Publisher: IOP Publishing
Date: 13-06-2013
DOI: 10.1088/0031-9155/58/13/4501
Abstract: Due to their small collecting volume, diodes are commonly used in small field dosimetry. However, the relative sensitivity of a diode increases with decreasing small field size. Conversely, small air gaps have been shown to cause a significant decrease in the sensitivity of a detector as the field size is decreased. Therefore, this study uses Monte Carlo simulations to look at introducing air upstream to diodes such that they measure with a constant sensitivity across all field sizes in small field dosimetry. Varying thicknesses of air were introduced onto the upstream end of two commercial diodes (PTW 60016 photon diode and PTW 60017 electron diode), as well as a theoretical unenclosed silicon chip using field sizes as small as 5 mm × 5 mm. The metric D(w,Q)/D(Det,Q) used in this study represents the ratio of the dose to a point of water to the dose to the diode active volume, for a particular field size and location. The optimal thickness of air required to provide a constant sensitivity across all small field sizes was found by plotting D(w,Q)/D(Det,Q) as a function of introduced air gap size for various field sizes, and finding the intersection point of these plots. That is, the point at which D(w,Q)/D(Det,Q) was constant for all field sizes was found. The optimal thickness of air was calculated to be 3.3, 1.15 and 0.10 mm for the photon diode, electron diode and unenclosed silicon chip, respectively. The variation in these results was due to the different design of each detector. When calculated with the new diode design incorporating the upstream air gap, k(f(clin),f(msr))(Q(clin),Q(msr)) was equal to unity to within statistical uncertainty (0.5%) for all three diodes. Cross-axis profile measurements were also improved with the new detector design. The upstream air gap could be implanted on the commercial diodes via a cap consisting of the air cavity surrounded by water equivalent material. The results for the unclosed silicon chip show that an ideal small field dosimetry diode could be created by using a silicon chip with a small amount of air above it.
Publisher: IOP Publishing
Date: 24-03-2014
Publisher: Springer Science and Business Media LLC
Date: 31-12-2020
Publisher: Taylor & Francis
Date: 13-03-2008
DOI: 10.1201/B15903-3
Publisher: Wiley
Date: 04-2017
DOI: 10.1002/MP.12108
Abstract: In this work, we develop a methodology for using Fricke gel dosimeters for dose distribution measurements surrounding high-density implants which circumvents artifact production by removing the obstruction during imaging. Custom 3D printed molds were used to set cavities in Fricke gel phantoms to allow for the suspension of high-density implants in different geometries. This allowed for the metal valve extracted from a temporary tissue expander to be suspended during irradiation, and removed during optical-CT scanning. The removal of the metal implant and subsequent backfilling of the remaining cavity with optically matched fluid prior to dose evaluation enables accurate optical-CT scanning of the gel dosimeters. Results have shown very good agreement between measured and calculated doses within 2 mm from the surface of the implant. Slight deviations are present within 1 mm of the interface. Artifacts in the form of radial streaking, cold spots, and hot spots were all reduced using this technique, enabling the broader and more accurate use of optical-CT for the imaging of gels containing opaque objects.
Publisher: Taylor & Francis
Date: 13-03-2008
DOI: 10.1201/B15903-5
Publisher: Springer Science and Business Media LLC
Date: 10-06-2021
Publisher: Springer Science and Business Media LLC
Date: 16-06-2021
DOI: 10.1038/S41598-021-92195-Y
Abstract: The advanced image sensors installed on now-ubiquitous smartphones can be used to detect ionising radiation in addition to visible light. Radiation incidents on a smartphone camera’s Complementary Metal Oxide Semiconductor (CMOS) sensor creates a signal which can be isolated from a visible light signal to turn the smartphone into a radiation detector. This work aims to report a detailed investigation of a well-reviewed smartphone application for radiation dosimetry that is available for popular smartphone devices under a calibration protocol that is typically used for the commercial calibration of radiation detectors. The iPhone 6s smartphone, which has a CMOS camera sensor, was used in this study. Black tape was utilized to block visible light. The Radioactivity counter app developed by Rolf-Dieter Klein and available on Apple’s App Store was installed on the device and tested using a calibrated radioactive source, calibration concrete pads with a range of known concentrations of radioactive elements, and in direct sunlight. The smartphone CMOS sensor is sensitive to radiation doses as low as 10 µGy/h, with a linear dose response and an angular dependence. The RadioactivityCounter app is limited in that it requires 4–10 min to offer a stable measurement. The precision of the measurement is also affected by heat and a smartphone’s battery level. Although the smartphone is not as accurate as a conventional detector, it is useful enough to detect radiation before the radiation reaches hazardous levels. It can also be used for personal dose assessments and as an alarm for the presence of high radiation levels.
Publisher: IOP Publishing
Date: 04-11-2019
Abstract: Shielding protocols such as NCRP 151, IAEA SRS 47 and IPEM 47 are commonly used for the design of radiotherapy facilities. Some work has been accomplished in updating the basic formula with the advent of IMRT but little consideration has been made for unflattened beams and stereotactic techniques apart from for facilities housing devices like the CyberKnife. The inevitable scenario of a stereotactic-only linear accelerator was considered in this study. The necessary shielding requirements were determined based on stereotactic data from a year's worth treatments from one clinic as well as further measurements of leakage, scatter and use factors. These values were compared to recommendations in the literature. While tenth value layer amounts, workload and barrier widths could be kept at the status quo, major changes could be made to the parameters of leakage, scatter and use factors while still maintaining safety. Some differences could also be seen for the use of IMRT factors. Current shielding protocols were found to inadequately describe methodology for the shielding of a stereotactic-only radiotherapy linac bunker, producing overly-conservative wall thicknesses which is in disagreement with the principles of ICRP.
Publisher: Springer Science and Business Media LLC
Date: 09-2012
DOI: 10.1007/S13246-012-0159-8
Abstract: Often CAD models already exist for parts of a geometry being simulated using GEANT4. Direct import of these CAD models into GEANT4 however, may not be possible and complex components may be difficult to define via other means. Solutions that allow for users to work around the limited support in the GEANT4 toolkit for loading predefined CAD geometries have been presented by others, however these solutions require intermediate file format conversion using commercial software. Here within we describe a technique that allows for CAD models to be directly loaded as geometry without the need for commercial software and intermediate file format conversion. Robustness of the interface was tested using a set of CAD models of various complexity for the models used in testing, no import errors were reported and all geometry was found to be navigable by GEANT4.
Publisher: Wiley
Date: 08-10-2013
DOI: 10.1118/1.4823776
Abstract: Intensity modulated radiotherapy (IMRT) treatments require more beam-on time and produce more linac head leakage to deliver similar doses to conventional, unmodulated, radiotherapy treatments. It is necessary to take this increased leakage into account when evaluating the results of radiation surveys around bunkers that are, or will be, used for IMRT. The recommended procedure of applying a monitor-unit based workload correction factor to secondary barrier survey measurements, to account for this increased leakage when evaluating radiation survey measurements around IMRT bunkers, can lead to potentially costly overestimation of the required barrier thickness. This study aims to provide initial guidance on the validity of reducing the value of the correction factor when applied to different radiation barriers (primary barriers, doors, maze walls, and other walls) by evaluating three different bunker designs. Radiation survey measurements of primary, scattered, and leakage radiation were obtained at each of five survey points around each of three different radiotherapy bunkers and the contribution of leakage to the total measured radiation dose at each point was evaluated. Measurements at each survey point were made with the linac gantry set to 12 equidistant positions from 0° to 330°, to assess the effects of radiation beam direction on the results. For all three bunker designs, less than 0.5% of dose measured at and alongside the primary barriers, less than 25% of the dose measured outside the bunker doors and up to 100% of the dose measured outside other secondary barriers was found to be caused by linac head leakage. Results of this study suggest that IMRT workload corrections are unnecessary, for survey measurements made at and alongside primary barriers. Use of reduced IMRT workload correction factors is recommended when evaluating survey measurements around a bunker door, provided that a subset of the measurements used in this study are repeated for the bunker in question. Reduction of the correction factor for other secondary barrier survey measurements is not recommended unless the contribution from leakage is separately evaluated.
Publisher: Springer Science and Business Media LLC
Date: 30-09-2020
DOI: 10.1038/S41598-020-73101-4
Abstract: This study aimed to evaluate the effect of nurse and doctor height on occupational dose to the temple during fluoroscopically guided cardiovascular procedures. Additionally, an evaluation of the relationship between doctor height and table height was performed. Staff exposed during fluoroscopic procedures may be at elevated risk of cardiovascular damage or oncogenesis and have demonstrated a higher incidence of subscapular cataracts. The heads of taller staff may be exposed to reduced levels of radiation due to the increased distance from the area of highest intensity X-ray scatter. Limited research has been performed investigating height as a predictor of head dose to nursing staff. The level of radiation dose at the level of the temple to the doctor (n = 25), scrub (n = 28), and scout nurse (n = 29) was measured in a prospective single-center, observational study using Philips DoseAware badges. Procedural characteristics were recorded for vascular and cardiac cases performed in three dedicated angiography suites. Data were also collected to investigate relationships between doctor height and table height. Data were collected for 1585 cardiac and 294 vascular procedures. Staff height was a statistically significant predictor of temple dose for doctors, scrub, and scout nurses when considering the full data s le. The log temple dose demonstrated an inverse relationship to staff height during cardiac procedures, but a positive relationship for scrub and scout nurses during vascular studies. This observational study has demonstrated that taller staff are exposed to less cranial exposure dose during fluoroscopically guided cardiac examinations but has revealed a positive correlation between height and temple dose during vascular procedures. It was also determined that doctor height was correlated with average procedural table height and that vascular access point influences the choice of table elevation.
Publisher: Oxford University Press (OUP)
Date: 26-10-2021
Abstract: Exposure to radiation during fluoroscopically guided cardiac procedures is a cause for concern for both the patient and staff. This study sought to compare the occupational and patient radiation dose during femoral and radially accessed invasive coronary angiography (CA). Occupational dose (µSv) was measured at the left temple of the cardiologist (n = 17), scrub (n = 27), and circulator nurse (n = 27) during 761 femoral and 671 radially accessed diagnostic coronary angiograms and percutaneous coronary intervention (PCI) procedures. Patient dose parameters of dose area product (DAP) (Gy.cm2) and air kerma (AK) (Gy) were also measured. Coronary angiography performed via the radial artery is associated with greater mean dose to the cardiologist, with the exception of procedures including only PCI. Results demonstrated that scrub nurses are exposed to higher mean doses than the cardiologist when using femoral access and similar doses during radial cases. Both AK and DAP were associated with a higher average dose for femoral PCI than radial, with DAP being significantly higher. Awareness of factors that increase the dose to staff and patients is vital to inform and improve practice. This study has demonstrated that access route during diagnostic CA and PCI influences both patient and staff dose. Radiation dose to in-room staff other than the fluoroscopic operator should be a focus of future research. In addition, all staff present during X-ray guided procedures should be provided with radiation education and adopt dose minimization strategies to reduce occupational exposures.
Publisher: Springer Science and Business Media LLC
Date: 10-02-2023
DOI: 10.1038/S41598-023-28704-Y
Abstract: The number and complexity of transcatheter procedures continue to increase, raising concerns regarding radiation exposure to patients and staff. Procedures such as transaortic valve implantations (TAVI) have led to cardiologists adopting higher dose techniques, such as digital subtraction angiography (DSA). This study compared the estimated patient and occupational eye dose during coronary angiography (CA), percutaneous coronary intervention (PCI), TAVI workups (TWU), TAVI, endovascular aneurysm repairs (EVAR), and other peripheral diagnostic (VD) and interventional (VI) vascular procedures. A quantitative analysis was performed on patient dose during 299 endovascular and 1498 cardiac procedures. Occupational dose was measured for the cardiologists (n = 24), vascular surgeons (n = 3), scrub (n = 32) and circulator nurses (n = 35). TAVI and EVAR were associated with the highest average dose for all staff, and significantly higher patient dose area product, probably attributable to the use of DSA. Scrub nurses were exposed to higher average doses than the operator and scout nurse during CA, VD and VI. Circulating nurses had the highest average levels of exposure during TAVI. This study has demonstrated that EVAR and TAVI have similar levels of occupational and patient dose, with a notable increase in circulator dose during TAVI. The use of DSA during cardiac procedures is associated with an increase in patient and staff dose, and cardiologists should evaluate whether DSA is necessary. Scrub nurses may be exposed to higher levels of occupational dose than the operator.
Publisher: Informa UK Limited
Date: 07-2021
DOI: 10.2147/JMDH.S316135
Publisher: Springer Science and Business Media LLC
Date: 23-05-2013
DOI: 10.1007/S13246-013-0197-X
Abstract: The computed tomography (CT) imaging artefacts that metallic medical implants produce in surrounding tissues are usually contoured and over-ridden during radiotherapy treatment planning. In cases where radiotherapy treatment beams unavoidably pass though implants, it is especially important to understand the imaging artefacts that may occur within the implants themselves. This study examines CT images of a set of simple metallic objects, immersed in water, in order to evaluate reliability and variability of CT numbers (Hounsfield units, HUs) within medical implants. Model implants with a range of sizes (heights from 2.2 to 49.6 mm), electron densities (from 2.3 to 7.7 times the electron density of water) and effective atomic numbers (from 3.9 to 9.0 times the effective atomic number of water in a CT X-ray beam) were created by stacking metal coins from several currencies. These 'implants' were CT scanned within a large (31.0 cm across) and a small (12.8 cm across) water phantom. Resulting HU values are as much as 50 % lower than the result of extrapolating standard electron density calibration data (obtained for tissue and bone densities) up to the metal densities and there is a 6 % difference between the results obtained by scanning with 120 and 140 kVp tube potentials. Profiles through the implants show localised cupping artefacts, within the implants, as well as a gradual decline in HU outside the implants that can cause the implants' sizes to be over estimated by 1.3-9.0 mm. These effects are exacerbated when the implants are scanned in the small phantom or at the side of the large phantom, due to reduced pre-hardening of the X-ray beam in these configurations. These results demonstrate the necessity of over-riding the densities of metallic implants, as well as their artefacts in tissue, in order to obtain accurate radiotherapy dose calculations.
Publisher: Springer Science and Business Media LLC
Date: 20-03-2014
DOI: 10.1007/S13246-014-0260-2
Abstract: Stereotactic radiosurgery treatments involve the delivery of very high doses for a small number of fractions. To date, there is limited data in terms of the skin dose for the very small field sizes used in these treatments. In this work, we determine relative surface doses for small size circular collimators as used in stereotactic radiosurgery treatments. Monte Carlo calculations were performed using the BEAMnrc code with a model of the Novalis Trilogy linear accelerator and the BrainLab circular collimators. The surface doses were calculated at the ICRP skin dose depth of 70 μm all using the 6 MV SRS x-ray beam. The calculated surface doses varied between 15 and 12 % with decreasing values as the field size increased from 4 to 30 mm. In comparison, surface doses were measured using Gafchromic EBT3 film positioned at the surface of a Virtual Water phantom. The absolute agreement between calculated and measured surface doses was better than 2.0 % which is well within the uncertainties of the Monte Carlo calculations and the film measurements. Based on these results, we have shown that the Gafchromic EBT3 film is suitable for surface dose estimates in very small size fields as used in SRS.
Publisher: Wiley
Date: 20-02-2019
DOI: 10.1002/ACM2.12547
Publisher: Springer Science and Business Media LLC
Date: 11-03-2021
Publisher: Wiley
Date: 12-2015
DOI: 10.1118/1.4934827
Abstract: A modification of the existing PVA-FX hydrogel has been made to investigate the use of a functionalised polymer in a Fricke gel dosimetry system to decrease Fe(3+) diffusion. The chelating agent, xylenol orange, was chemically bonded to the gelling agent, polyvinyl alcohol (PVA) to create xylenol orange functionalised PVA (XO-PVA). A gel was created from the XO-PVA (20% w/v) with ferrous sulfate (0.4 mM) and sulfuric acid (50 mM). This resulted in an optical density dose sensitivity of 0.014 Gy(-1), an auto-oxidation rate of 0.0005 h(-1), and a diffusion rate of 0.129 mm(2) h(-1) an 8% reduction compared to the original PVA-FX gel, which in practical terms adds approximately 1 h to the time span between irradiation and accurate read-out. Because this initial method of chemically bonding xylenol orange to polyvinyl alcohol has inherently low conversion, the improvement on existing gel systems is minimal when compared to the drawbacks. More efficient methods of functionalising polyvinyl alcohol with xylenol orange must be developed for this system to gain clinical relevance.
Publisher: Elsevier BV
Date: 11-2016
DOI: 10.1016/J.EJMP.2016.10.021
Abstract: The purpose of this study was to evaluate the suitability of the Daily QA 3 (Sun Nuclear Corporation, Melbourne, USA) device as a safe quality assurance device for control of machine specific parameters, such as linear accelerator output, beam quality and beam flatness and symmetry. Measurements were performed using three Varian 2300iX linear accelerators. The suitability of Daily QA 3 as a device for quality control of linear accelerator parameters was investigated for both 6 and 10MV photons and 6, 9, 12, 15 and 18MeV electrons. Measurements of machine specific using the Daily QA 3 device were compared to corresponding measurements using a simpler constancy meter, Farmer chamber and plane parallel ionisation chamber in a water tank. The Daily QA 3 device showed a linear dose response making it a suitable device for detection of output variations during routine measurements. It was noted that over estimations of variations compared with Farmer chamber readings were seen if the Daily QA 3 wasn't calibrated for output and sensitivity on a regular eight to ten monthly basis. Temperature-pressure correction factors calculated by Daily QA 3 also contributed towards larger short term variations seen in output measurements. Energy, symmetry and flatness variations detected by Daily QA 3 were consistent with measurements performed in water tank using a parallel plate chamber. It was concluded that the Daily QA 3 device is suitable for routine daily and fortnightly quality assurance of linear accelerator beam parameters however a regular eight-ten monthly dose and detector array calibration will improve error detection capabilities of the device.
Publisher: Elsevier BV
Date: 11-2016
DOI: 10.1016/J.EJMP.2016.10.020
Abstract: In this work, the apparent treatment dose that kV planar or CBCT imaging contributes to Gafchromic EBT3 film used for in vivo dosimetry, was investigated. Gafchromic EBT3 film pieces were attached to a variety of phantoms and irradiated using the linear accelerator's built-in kV imaging system, in both kV planar mode and CBCT mode. To evaluate the sensitivity of the film in the clinical scenario where dose contributions are received from both imaging and treatment, additional pieces of film were irradiated using base doses of 50cGy and then irradiated using selected kV planar and CBCT techniques. For kV planar imaging, apparent treatment doses of up to 3.4cGy per image pair were seen. For CBCT, apparent treatment doses ranged from 0.22cGy to 3.78cGy. These apparent doses were reproducible with and without the inclusion of the 50cGy base dose. The contribution of apparent treatment dose from both planar kV as well as CBCT imaging can be detected, even in conjunction with an actual treatment dose. The magnitude of the apparent dose was found to be dependent on patient geometry, scanning protocol, and measurement location. It was found that the apparent treatment dose from the imaging could add up to 8% of additional uncertainty to the in vivo dosimetry result, if not taken into account. It is possible for this apparent treatment dose to be accounted for by subtraction of the experimentally determined apparent doses from in vivo measurements, as demonstrated in this work.
Publisher: Springer Science and Business Media LLC
Date: 06-02-2017
DOI: 10.1007/S13246-017-0523-9
Abstract: This study evaluated the feasibility of combining the 'zero-scan' (ZS) X-ray computed tomography (CT) based polymer gel dosimeter (PGD) readout with adaptive mean (AM) filtering for improving the signal to noise ratio (SNR), and to compare these results with available average scan (AS) X-ray CT readout techniques. NIPAM PGD were manufactured, irradiated with 6 MV photons, CT imaged and processed in Matlab. AM filter for two iterations, with 3 × 3 and 5 × 5 pixels (kernel size), was used in two scenarios (a) the CT images were subjected to AM filtering (pre-processing) and these were further employed to generate AS and ZS gel images, and (b) the AS and ZS images were first reconstructed from the CT images and then AM filtering was carried out (post-processing). SNR was computed in an ROI of 30 × 30 for different pre and post processing cases. Results showed that the ZS technique combined with AM filtering resulted in improved SNR. Using the previously-recommended 25 images for reconstruction the ZS pre-processed protocol can give an increase of 44% and 80% in SNR for 3 × 3 and 5 × 5 kernel sizes respectively. However, post processing using both techniques and filter sizes introduced blur and a reduction in the spatial resolution. Based on this work, it is possible to recommend that the ZS method may be combined with pre-processed AM filtering using appropriate kernel size, to produce a large increase in the SNR of the reconstructed PGD images.
Publisher: Wiley
Date: 10-2014
DOI: 10.1118/1.4894728
Abstract: Two diodes which do not require correction factors for small field relative output measurements are designed and validated using experimental methodology. This was achieved by adding an air layer above the active volume of the diode detectors, which canceled out the increase in response of the diodes in small fields relative to standard field sizes. Due to the increased density of silicon and other components within a diode, additional electrons are created. In very small fields, a very small air gap acts as an effective filter of electrons with a high angle of incidence. The aim was to design a diode that balanced these perturbations to give a response similar to a water-only geometry. Three thicknesses of air were placed at the proximal end of a PTW 60017 electron diode (PTWe) using an adjustable "air cap". A set of output ratios (ORDet (fclin) ) for square field sizes of side length down to 5 mm was measured using each air thickness and compared to ORDet (fclin) measured using an IBA stereotactic field diode (SFD). kQclin,Qmsr (fclin,fmsr) was transferred from the SFD to the PTWe diode and plotted as a function of air gap thickness for each field size. This enabled the optimal air gap thickness to be obtained by observing which thickness of air was required such that kQclin,Qmsr (fclin,fmsr) was equal to 1.00 at all field sizes. A similar procedure was used to find the optimal air thickness required to make a modified Sun Nuclear EDGE detector (EDGEe) which is "correction-free" in small field relative dosimetry. In addition, the feasibility of experimentally transferring kQclin,Qmsr (fclin,fmsr) values from the SFD to unknown diodes was tested by comparing the experimentally transferred kQclin,Qmsr (fclin,fmsr) values for unmodified PTWe and EDGEe diodes to Monte Carlo simulated values. 1.0 mm of air was required to make the PTWe diode correction-free. This modified diode (PTWeair) produced output factors equivalent to those in water at all field sizes (5-50 mm). The optimal air thickness required for the EDGEe diode was found to be 0.6 mm. The modified diode (EDGEeair) produced output factors equivalent to those in water, except at field sizes of 8 and 10 mm where it measured approximately 2% greater than the relative dose to water. The experimentally calculated kQclin,Qmsr (fclin,fmsr) for both the PTWe and the EDGEe diodes (without air) matched Monte Carlo simulated results, thus proving that it is feasible to transfer kQclin,Qmsr (fclin,fmsr) from one commercially available detector to another using experimental methods and the recommended experimental setup. It is possible to create a diode which does not require corrections for small field output factor measurements. This has been performed and verified experimentally. The ability of a detector to be "correction-free" depends strongly on its design and composition. A nonwater-equivalent detector can only be "correction-free" if competing perturbations of the beam cancel out at all field sizes. This should not be confused with true water equivalency of a detector.
Publisher: IOP Publishing
Date: 03-10-2017
Abstract: In this work, a methodology for using a smartphone camera, in conjunction with a light-tight box operating in reflective transmission mode, is investigated as a proof of concept for use as a film dosimetry system. An imaging system was designed to allow the camera of a smartphone to be used as a pseudo densitometer. Ten pieces of Gafchromic EBT3 film were irradiated to doses up to 16.89 Gy and used to evaluate the effects of reproducibility and orientation, as well as the ability to create an accurate dose response curve for the smartphone based dosimetry system, using all three colour channels. Results were compared to a flatbed scanner system. Overall uncertainty was found to be best for the red channel with an uncertainty of 2.4% identified for film irradiated to 2.5 Gy and digitised using the smartphone system. This proof of concept exercise showed that although uncertainties still exceed a flatbed scanner system, the smartphone system may be useful for providing point dose measurements in situations where conventional flatbed scanners (or other dosimetry systems) are unavailable or unaffordable.
Publisher: Springer Science and Business Media LLC
Date: 28-07-2020
Publisher: Springer Science and Business Media LLC
Date: 09-11-2020
Publisher: Springer Science and Business Media LLC
Date: 03-2023
DOI: 10.1007/S13246-023-01226-7
Abstract: X-ray guided procedures are being performed by an increasing variety of medical specialties. Due to improvements in vascular transcatheter therapies, there is an increasing overlap of imaged anatomy between medical specialties. There is concern that non-radiology fluoroscopic operators may not have sufficient training to be well informed of the potential implications of radiation exposure and mitigation strategies to reduce dose. This was a prospective, observational, single center study to compare occupational and patient dose levels when imaging different anatomical regions during fluoroscopically guided cardiac and endovascular procedures. Occupational radiation dose was measured at the level of the temple of 24 cardiologists and 3 vascular surgeons (n = 1369), 32 scrub nurses (n = 1307) and 35 circulating nurses (n = 885). The patient dose was recorded for procedures (n = 1792) performed in three angiography suites. Abdominal imaging during endovascular aneurysm repair (EVAR) procedures was associated with a comparatively high average patient, operator and scrub nurse dose despite additional table-mounted lead shields. Air kerma was relatively high for procedures performed in the chest, and chest + pelvis. Higher dose area product and staff eye dose were recorded during procedures of the chest + pelvis due to the use of digital subtraction angiography to evaluate access route prior to/during transaortic valve implantation. Scrub nurses were exposed to higher average radiation levels than the operator during some procedures. Staff should be cognizant of the potentially higher radiation burden to patients and exposed personnel during EVAR procedures and cardiac procedures using digital subtraction angiography.
Publisher: Springer Science and Business Media LLC
Date: 06-2008
DOI: 10.1007/BF03178587
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Publisher: Springer Science and Business Media LLC
Date: 03-2010
Publisher: Springer Science and Business Media LLC
Date: 08-02-2021
Publisher: IOP Publishing
Date: 12-11-2002
DOI: 10.1088/0031-9155/47/23/310
Abstract: Post-irradiation changes in the linear attenuation coefficient, mu, of polymer gel dosimeters give rise to a change which can be measured with x-ray computed tomography. Polymer gel dosimeters were manufactured consisting of 3% (by weight) acrylamide and 3% N,N'-methylene-bis-acrylamide comonomers dissolved in aqueous gelatin (5% gelatin by total weight and 89% de-ionized distilled water). Mu was measured in a collimated radiation beam of photons from an 241Am source. Density, rho, of polymer gel dosimeters was measured using volumetric flasks with capillary stoppers. The measured post-irradiation data of mu was plotted against the data of rho for different batches, and linear least squares fits gave r2 values of 0.99605 and 0.99953, with P values of less than 0.001. This confirms that the post-irradiation change in mu is proportional to that of rho. The change in rho implies a change in volume regardless of the evaluation modality of the polymer gel dosimeter.
Publisher: Springer International Publishing
Date: 2015
Publisher: Springer Science and Business Media LLC
Date: 08-02-2019
Publisher: Elsevier BV
Date: 10-2020
Publisher: Springer Science and Business Media LLC
Date: 27-05-2020
Publisher: Elsevier BV
Date: 2021
Publisher: Springer Science and Business Media LLC
Date: 30-12-2020
DOI: 10.1038/S41598-020-80349-3
Abstract: An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Publisher: Springer Science and Business Media LLC
Date: 25-07-2019
DOI: 10.1007/S13246-019-00782-1
Abstract: Conservatism in the shielding of linear accelerator bunkers is engrained in the methodology of international protocols and guidelines. However, the degree to which this cautious and prudent approach is necessary should be judged against the International Committee of Radiation Protection's principles of exposure justification and optimisation. Radiation survey data from 75 concrete barriers was aggregated and compared to exposure predictions from three popular protocols in order to assess any conservatism in factors used to calculate scatter, leakage and beam penetration. These findings, in addition to a list of common conservative practices, were then used to tally the possible fiscal impact of an over-conservative approach to linear accelerator bunker shielding. While primary beam penetration was accurately predicted, stated conservatisms in scatter and leakage was found to be largely misplaced. An estimated total factor of conservatism calculated from a tally was found to be in agreement with literature values of radiotherapist occupational exposure. This factor amounted to a cost increase of 43% for a single bunker if all conservative assumptions were made. There are aspects of linear accelerator shielding design that have been shown to be overly conservative, beyond what is justifiable by the International Committee of Radiation Protection. Some adjustment to international protocol methodology may be required.
Publisher: The Royal Australian and New Zealand College of Radiologists
Date: 2014
Publisher: Springer Science and Business Media LLC
Date: 16-12-2020
Publisher: Wiley
Date: 26-06-2018
DOI: 10.1002/ACM2.12395
Publisher: Wiley
Date: 22-06-2018
DOI: 10.1002/ACM2.12394
Publisher: Springer Science and Business Media LLC
Date: 10-09-2019
Publisher: Oxford University Press (OUP)
Date: 03-2021
DOI: 10.1093/RPD/NCAB037
Abstract: Shielded garments are widely recommended for occupational radiation protection in diagnostic and interventional radiology. This study investigated a novel method for efficiently verifying shielded garment integrity while simultaneously acquiring data for lead-equivalence measurements, using two-dimensional topogram images from computed tomography (CT) scanners. This method was tested against more-conventional measurements with superficial and orthovoltage radiotherapy treatment beams, for 12 shielded garments containing 3 different lead-free shielding materials. Despite some energy-dependent results, all shielded garments approximately achieved their specified lead-equivalence for the energy range expected during clinical use for fluoroscopy procedures, except for three shielded skirts that required two layers of material to be overlapped at the front. All lead-equivalence measurements from CT topograms agreed with or conservatively underestimated the kV narrow-beam results. This method is potentially useful for independently assessing the shielding properties of new shielded garments and performing annual checks for damage or degradation of existing shielded garments.
Publisher: Springer Singapore
Date: 30-05-2019
Publisher: IOP Publishing
Date: 05-2009
Publisher: IOP Publishing
Date: 12-03-2015
DOI: 10.1088/0031-9155/60/6/2587
Abstract: This study aimed to provide a detailed evaluation and comparison of a range of modulated beam evaluation metrics, in terms of their correlation with QA testing results and their variation between treatment sites, for a large number of treatments. Ten metrics including the modulation index (MI), fluence map complexity, modulation complexity score (MCS), mean aperture displacement (MAD) and small aperture score (SAS) were evaluated for 546 beams from 122 intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment plans targeting the anus, rectum, endometrium, brain, head and neck and prostate. The calculated sets of metrics were evaluated in terms of their relationships to each other and their correlation with the results of electronic portal imaging based quality assurance (QA) evaluations of the treatment beams. Evaluation of the MI, MAD and SAS suggested that beams used in treatments of the anus, rectum, head and neck were more complex than the prostate and brain treatment beams. Seven of the ten beam complexity metrics were found to be strongly correlated with the results from QA testing of the IMRT beams (p < 0.00008). For ex le, values of SAS (with multileaf collimator apertures narrower than 10 mm defined as 'small') less than 0.2 also identified QA passing IMRT beams with 100% specificity. However, few of the metrics are correlated with the results from QA testing of the VMAT beams, whether they were evaluated as whole 360° arcs or as 60° sub-arcs. Select evaluation of beam complexity metrics (at least MI, MCS and SAS) is therefore recommended, as an intermediate step in the IMRT QA chain. Such evaluation may also be useful as a means of periodically reviewing VMAT planning or optimiser performance.
Publisher: Springer Science and Business Media LLC
Date: 05-07-2016
DOI: 10.1007/S13246-016-0461-Y
Abstract: Given the difficulty and potential time- or financial-costs associated with accurate small field dosimetry, this study aimed to establish the clinical necessity of obtaining accurate small field output factor measurements and to evaluate the effects on planned doses that could arise if accurate measurements are not used in treatment planning dose calculations. Isocentre doses, in heterogeneous patient anatomy, were calculated and compared for 571 beams from 48 clinical radiotherapy treatments, using a clinical radiotherapy treatment planning system, with reference to two different sets of beam configuration data. One set of beam configuration data included field output factors (total scatter factors) from precisely positioned and response-corrected diode measurements and the other included field output factors measured using a conventional technique that would have been better suited to larger field measurements. Differences between the field output factor measurements made with the two different techniques equated to 14.2 % for the 6 [Formula: see text] 6 mm[Formula: see text] field, 1.8 % for the 12 [Formula: see text] 12 mm[Formula: see text] field, and less than 0.5 % for the larger fields. This led to isocentre dose differences of up to 3.3 % in routine clinical fields smaller than 9 mm across and and up to 11 % in convoluted fields smaller than 15 mm across. If field widths smaller than 15 mm are used clinically, then accurate measurement (or-remeasurement) of small field output factors in the treatment planning system's beam data is required in order to achieve dose calculation accuracy within 3 %. If such measurements are not completed, then errors in excess of 10 % may occur if very small, narrow, concave or convoluted treatment fields are used.
Publisher: IOP Publishing
Date: 2004
Publisher: Elsevier BV
Date: 07-2012
Publisher: Wiley
Date: 22-08-2011
DOI: 10.1118/1.3626487
Abstract: This study provides a simple method for improving precision of X-ray computed tomography (CT) scans of irradiated polymer gel dosimetry. The noise affecting CT scans of irradiated gels has been an impediment to the use of clinical CT scanners for gel dosimetry studies. In this study, it is shown that multiple scans of a single PAGAT gel dosimeter can be used to extrapolate a "zero-scan" image which displays a similar level of precision to an image obtained by averaging multiple CT images, without the compromised dose measurement resulting from the exposure of the gel to radiation from the CT scanner. When extrapolating the zero-scan image, it is shown that exponential and simple linear fits to the relationship between Hounsfield unit and scan number, for each pixel in the image, provide an accurate indication of gel density. It is expected that this work will be utilized in the analysis of three-dimensional gel volumes irradiated using complex radiotherapy treatments.
Publisher: Springer Science and Business Media LLC
Date: 06-03-2015
DOI: 10.1007/S13246-015-0334-9
Abstract: There have been substantial advances in small field dosimetry techniques and technologies, over the last decade, which have dramatically improved the achievable accuracy of small field dose measurements. This educational note aims to help radiation oncology medical physicists to apply some of these advances in clinical practice. The evaluation of a set of small field output factors (total scatter factors) is used to exemplify a detailed measurement and simulation procedure and as a basis for discussing the possible effects of simplifying that procedure. Field output factors were measured with an unshielded diode and a micro-ionisation chamber, at the centre of a set of square fields defined by a micro-multileaf collimator. Nominal field sizes investigated ranged from 6 × 6 to 98 × 98 mm(2). Diode measurements in fields smaller than 30 mm across were corrected using response factors calculated using Monte Carlo simulations of the diode geometry and daisy-chained to match micro-chamber measurements at intermediate field sizes. Diode measurements in fields smaller than 15 mm across were repeated twelve times over three separate measurement sessions, to evaluate the reproducibility of the radiation field size and its correspondence with the nominal field size. The five readings that contributed to each measurement on each day varied by up to 0.26 %, for the "very small" fields smaller than 15 mm, and 0.18 % for the fields larger than 15 mm. The diode response factors calculated for the unshielded diode agreed with previously published results, within uncertainties. The measured dimensions of the very small fields differed by up to 0.3 mm, across the different measurement sessions, contributing an uncertainty of up to 1.2 % to the very small field output factors. The overall uncertainties in the field output factors were 1.8 % for the very small fields and 1.1 % for the fields larger than 15 mm across. Recommended steps for acquiring small field output factor measurements for use in radiotherapy treatment planning system beam configuration data are provided.
Publisher: Springer Science and Business Media LLC
Date: 28-11-2012
DOI: 10.1007/S13246-012-0167-8
Abstract: Cloud computing allows for vast computational resources to be leveraged quickly and easily in bursts as and when required. Here we describe a technique that allows for Monte Carlo radiotherapy dose calculations to be performed using GEANT4 and executed in the cloud, with relative simulation cost and completion time evaluated as a function of machine count. As expected, simulation completion time decreases as 1/n for n parallel machines, and relative simulation cost is found to be optimal where n is a factor of the total simulation time in hours. Using the technique, we demonstrate the potential usefulness of cloud computing as a solution for rapid Monte Carlo simulation for radiotherapy dose calculation without the need for dedicated local computer hardware as a proof of principal.
Publisher: IOP Publishing
Date: 11-08-2010
Publisher: IOP Publishing
Date: 11-2010
Publisher: Springer Science and Business Media LLC
Date: 09-11-2020
Publisher: Springer Science and Business Media LLC
Date: 26-08-2020
DOI: 10.1007/S13246-019-00791-0
Abstract: The purpose of this study is to define departmental action limits for energy percentage variation measured by means of step-wedge helical Tomotherapy quality assurance module. In idual charts using the Statistical Process Control techniques have been used to identify retrospectively out-of-control situations ascribable to documented actions performed on the Tomotherapy system. Using the in-control data of our analysis process capability indices (c
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.MEDDOS.2017.10.003
Abstract: This study aimed to provide guidance on the advantages and limitations of a new optimizer, "photon optimizer" (PO), when compared with its predecessor, "progressive resolution optimizer" (PRO), for intensity-modulated arc therapy (IMAT) plans. Eleven study plans that included a cohort of prostate, head and neck, and brain treatment sites were optimized using both PRO and PO algorithms. A plan template using the same objectives for the same number of iterations was used for each optimized plan to obtain hypothetical treatment plans that would be comparable with a clinical plan. Analysis was performed using plan conformity-based parameters such as target volume coverage factor, conformation number and homogeneity indices, and plan complexity assessment parameters such as small aperture score, modulation indices, and monitor unit variation with arc angle for prostate, brain and head, and neck IMAT treatment plans. Plan conformality analysis demonstrated that conformation numbers, target volume coverage factors, and homogeneity indices produced by the 2 optimizers were comparable for most anatomic sites. IMAT treatment plans produced using the PRO optimizer were found to be less complex than plans produced using the PO optimizer, in terms of multileaf collimator (MLC) leaf position variability and modulation complexity scores. Similarly, the PRO optimizer was shown to produce treatment plans that used fewer monitor units (and generally fewer monitor unit per degree of arc rotation) than PO optimizer. This study demonstrated that the PO optimizer can produce IMAT treatment plans with a similar degree of dose conformity to the target volume and generally improved organ at risk sparing, compared with the PRO optimizer. Better coverage to organs at risk produced by plans optimized using PO was observed to have higher MLC variability and monitor units. Therefore, careful evaluation of treatment plan conformity and complexity before assessing its deliverability is recommended when implementing the routine use of PO optimizer.
Publisher: Elsevier BV
Date: 2020
Publisher: IOP Publishing
Date: 04-2004
DOI: 10.1088/0031-9155/49/9/003
Abstract: In recent years there has been a large amount of research into the potential use of radiation sensitive gels for three-dimensional verification of clinical radiotherapy doses. In this paper we report the use of a MAGIC gel dosimeter (Fong et al 2001 Phys. Med. Biol. 46 3105) for the verification of a specific patient's radiation therapy dose distribution. A 69-year-old male patient presented with a squamous cell carcinoma extending approximately 180 degrees across the top of the scalp (anterior to posterior) and from just over midline to 90 degrees left of the skull. The patient's treatment was commenced using two electron fields. For gel dosimetry, phantoms were produced in which the outer surface spatially corresponded to the outer contours of the patient's anatomy in the region of irradiation. The phantoms were treated with either electrons or intensity modulated radiation therapy (IMRT) with photons. The results identified a hot spot between the matched electron fields and confirmed the more homogeneous dose distribution produced by the IMRT planning system. The IMRT plan was then clinically implemented. The application of a clinical dose to a phantom shaped to a specific patient as well as the ability to select a slice at will during phantom imaging means that gel dosimetry can no longer be considered to simply have potential alone, but is now in fact a useful dosimetric tool.
Publisher: Springer Science and Business Media LLC
Date: 18-11-2016
DOI: 10.1007/S13246-015-0401-2
Abstract: This study aims to help broaden the use of electronic portal imaging devices (EPIDs) for pre-treatment patient positioning verification, from photon-beam radiotherapy to photon- and electron-beam radiotherapy, by proposing and testing a method for acquiring clinically-useful EPID images of patient anatomy using electron beams, with a view to enabling and encouraging further research in this area. EPID images used in this study were acquired using all available beams from a linac configured to deliver electron beams with nominal energies of 6, 9, 12, 16 and 20 MeV, as well as photon beams with nominal energies of 6 and 10 MV. A widely-available heterogeneous, approximately-humanoid, thorax phantom was used, to provide an indication of the contrast and noise produced when imaging different types of tissue with comparatively realistic thicknesses. The acquired images were automatically calibrated, corrected for the effects of variations in the sensitivity of in idual photodiodes, using a flood field image. For electron beam imaging, flood field EPID calibration images were acquired with and without the placement of blocks of water-equivalent plastic (with thicknesses approximately equal to the practical range of electrons in the plastic) placed upstream of the EPID, to filter out the primary electron beam, leaving only the bremsstrahlung photon signal. While the electron beam images acquired using a standard (unfiltered) flood field calibration were observed to be noisy and difficult to interpret, the electron beam images acquired using the filtered flood field calibration showed tissues and bony anatomy with levels of contrast and noise that were similar to the contrast and noise levels seen in the clinically acceptable photon beam EPID images. The best electron beam imaging results (highest contrast, signal-to-noise and contrast-to-noise ratios) were achieved when the images were acquired using the higher energy electron beams (16 and 20 MeV) when the EPID was calibrated using an intermediate (12 MeV) electron beam energy. These results demonstrate the feasibility of acquiring clinically-useful EPID images of patient anatomy using electron beams and suggest important avenues for future investigation, thus enabling and encouraging further research in this area. There is manifest potential for the EPID imaging method proposed in this work to lead to the clinical use of electron beam imaging for geometric verification of electron treatments in the future.
Publisher: Elsevier BV
Date: 06-2017
DOI: 10.1016/J.EJMP.2017.05.051
Abstract: This study evaluates the radiological properties of different 3D printing materials for a range of photon energies, including kV and MV CT imaging and MV radiotherapy beams. The CT values of a number of materials were measured on an Aquilion One CT scanner at 80kVp, 120kVp and a Tomotherapy Hi Art MVCT imaging beam. Attenuation of the materials in a 6MV radiotherapy beam was investigated. Plastic filaments printed with various infill densities have CT values of -743±4, -580±1 and -113±3 in 120kVp CT images which approximate the CT values of low-density lung, high-density lung and soft tissue respectively. Metal-infused plastic filaments printed with a 90% infill density have CT values of 658±1 and 739±6 in MVCT images which approximate the attenuation of cortical bone. The effective relative electron density RED 3D printers can model a variety of body tissues which can be used to create phantoms useful for both imaging and dosimetric studies.
Publisher: Springer Science and Business Media LLC
Date: 20-06-2016
DOI: 10.1007/S13246-016-0454-X
Abstract: This study provides a bulk, retrospective analysis of 151 breast and chest wall radiotherapy treatment plans, as a small-scale demonstration of the potential breadth and value of the information that may be obtained from clinical data mining. The treatments were planned at three centres belonging to one organisation over a period of 3 months. All 151 plans were used to evaluate inter-centre consistency and compliance with a local planning protocol. A subset of 79 plans, from one centre, were used in a more detailed evaluation of the effects of anatomical asymmetry on heart and lung dose, the effects of a metallic temporary tissue expander port on dose homogeneity and the overall conformity and homogeneity achieved in routine breast treatment planning. Differences in anatomical structure contouring and nomenclature were identified between the three centres, with all centres showing some non-compliance with the local planning protocol. When evaluated against standard conformity indices, these breast plans performed relatively poorly. However, when evaluated against recommended organ-at-risk tolerances, all evaluated plans performed sufficiently well that tighter planning tolerances could be recommended for future planning. Heart doses calculated in left breast and chest wall treatments were significantly higher than heart doses calculated in right sided breast and chest wall treatments (p < 0.001). In the treatment involving a temporary tissue expander, the inflated implant effectively pushed the targeted breast tissue away from the healthy tissues, leading to a dose distribution that was relatively conformal, although attenuation through the tissue expander's metallic port may have been underestimated by the treatment planning system. The results of this study exemplify the use of bulk treatment planning data to evaluate clinical workloads and inform ongoing treatment planning.
Publisher: Springer Science and Business Media LLC
Date: 29-11-2011
Publisher: Elsevier BV
Date: 06-2013
DOI: 10.1016/J.EJMP.2012.04.007
Abstract: In this study the interplay effects for Enhanced Dynamic Wedge (EDW) treatments are experimentally investigated. Single and multiple field EDW plans for different wedge angles were delivered to a phantom and detector on a moving platform, with various periods, litudes for parallel and perpendicular motions. A four field 4D CT planned lung EDW treatment was delivered to a dummy tumor over four fractions. For the single field parallel case the litude and the period of motion both affect the interplay resulting in the appearance of a step function and penumbral cut off with the discrepancy worst where collimator-tumor speed is similar. For perpendicular motion the litude of tumor motion is the only dominant factor. For large wedge angle the dose discrepancy is more pronounced compared to the small wedge angle for the same field size and litude-period values. For a small field size i.e. 5 × 5 cm(2) the loss of wedged distribution was observed for both 60° and 15° wedge angles for parallel and perpendicular motions. Film results from 4D CT planned delivery displayed a mix of over and under dosages over 4 fractions, with the gamma pass rate of 40% for the averaged film image at 3%/1 mm DTA (Distance to Agreement). Amplitude and period of the tumor motion both affect the interplay for single and multi-field EDW treatments and for a limited (4 or 5) fraction delivery there is a possibility of non-averaging of the EDW interplay.
Publisher: Springer Science and Business Media LLC
Date: 09-05-2014
DOI: 10.1007/S13246-014-0274-9
Abstract: The planning of IMRT treatments requires a compromise between dose conformity (complexity) and deliverability. This study investigates established and novel treatment complexity metrics for 122 IMRT beams from prostate treatment plans. The Treatment and Dose Assessor software was used to extract the necessary data from exported treatment plan files and calculate the metrics. For most of the metrics, there was strong overlap between the calculated values for plans that passed and failed their quality assurance (QA) tests. However, statistically significant variation between plans that passed and failed QA measurements was found for the established modulation index and for a novel metric describing the proportion of small apertures in each beam. The 'small aperture score' provided threshold values which successfully distinguished deliverable treatment plans from plans that did not pass QA, with a low false negative rate.
Publisher: IOP Publishing
Date: 09-10-2012
DOI: 10.1088/0031-9155/57/21/6947
Abstract: The purpose of this study was to investigate the effect of very small air gaps (less than 1 mm) on the dosimetry of small photon fields used for stereotactic treatments. Measurements were performed with optically stimulated luminescent dosimeters (OSLDs) for 6 MV photons on a Varian 21iX linear accelerator with a Brainlab µMLC attachment for square field sizes down to 6 mm × 6 mm. Monte Carlo simulations were performed using EGSnrc C++ user code cavity. It was found that the Monte Carlo model used in this study accurately simulated the OSLD measurements on the linear accelerator. For the 6 mm field size, the 0.5 mm air gap upstream to the active area of the OSLD caused a 5.3% dose reduction relative to a Monte Carlo simulation with no air gap. A hypothetical 0.2 mm air gap caused a dose reduction >2%, emphasizing the fact that even the tiniest air gaps can cause a large reduction in measured dose. The negligible effect on an 18 mm field size illustrated that the electronic disequilibrium caused by such small air gaps only affects the dosimetry of the very small fields. When performing small field dosimetry, care must be taken to avoid any air gaps, as can be often present when inserting detectors into solid phantoms. It is recommended that very small field dosimetry is performed in liquid water. When using small photon fields, sub-millimetre air gaps can also affect patient dosimetry if they cannot be spatially resolved on a CT scan. However the effect on the patient is debatable as the dose reduction caused by a 1 mm air gap, starting out at 19% in the first 0.1 mm behind the air gap, decreases to <5% after just 2 mm, and electronic equilibrium is fully re-established after just 5 mm.
Publisher: IOP Publishing
Date: 12-01-2015
Publisher: IOP Publishing
Date: 24-03-2014
Publisher: Elsevier BV
Date: 06-2017
DOI: 10.1016/J.EJMP.2017.05.052
Abstract: The aims of this study were to investigate machine beam parameters using the TomoTherapy quality assurance (TQA) tool, establish a correlation to patient delivery quality assurance results and to evaluate the relationship between energy variations detected using different TQA modules. TQA daily measurement results from two treatment machines for periods of up to 4years were acquired. Analyses of beam quality, helical and static output variations were made. Variations from planned dose were also analysed using Statistical Process Control (SPC) technique and their relationship to output trends were studied. Energy variations appeared to be one of the contributing factors to delivery output dose seen in the analysis. Ion chamber measurements were reliable indicators of energy and output variations and were linear with patient dose verifications.
Publisher: Springer Science and Business Media LLC
Date: 10-07-2019
Publisher: IOP Publishing
Date: 05-05-2004
DOI: 10.1088/0031-9155/49/10/N02
Abstract: Dose resolution, DdeltaP, is becoming a common method for characterizing the performance of a gel dosimeter. In this note we examine how the goodness of fit of the calibration function affects DdeltaP and show that its inclusion in the calculation of DdeltaP is essential to avoid overestimating the performance of the gel.
Publisher: Springer Science and Business Media LLC
Date: 30-05-2015
DOI: 10.1007/S13246-015-0349-2
Abstract: Given that there is increasing recognition of the effect that sub-millimetre changes in collimator position can have on radiotherapy beam dosimetry, this study aimed to evaluate the potential variability in small field collimation that may exist between otherwise matched linacs. Field sizes and field output factors were measured using radiochromic film and an electron diode, for jaw- and MLC-collimated fields produced by eight dosimetrically matched Varian iX linacs (Varian Medical Systems, Palo Alto, USA). This study used nominal sizes from 0.6 × 0.6 to 10 × 10 cm(2), for jaw-collimated fields, and from 1 × 1 to 10 × 10 cm(2) for MLC-collimated fields, delivered from a zero (head up, beam directed vertically downward) gantry angle. Differences between the field sizes measured for the eight linacs exceeded the uncertainty of the film measurements and the repositioning uncertainty of the jaws and MLCs on one linac. The dimensions of fields defined by MLC leaves were more consistent between linacs, while also differing more from their nominal values than fields defined by orthogonal jaws. The field output factors measured for the different linacs generally increased with increasing measured field size for the nominal 0.6 × 0.6 to 1 × 1 cm(2) fields, and became consistent between linacs for nominal field sizes of 2 × 2 cm(2) and larger. The inclusion in radiotherapy treatment planning system beam data of small field output factors acquired in fields collimated by jaws (rather than the more-reproducible MLCs), associated with either the nominal or the measured field sizes, should be viewed with caution. The size and reproducibility of the fields (especially the small fields) used to acquire treatment planning data should be investigated thoroughly as part of the linac or planning system commissioning process. Further investigation of these issues, using different linac models, collimation systems and beam orientations, is recommended.
Publisher: Wiley
Date: 21-07-2017
DOI: 10.1002/ACM2.12136
Publisher: Elsevier BV
Date: 2020
Publisher: IOP Publishing
Date: 19-10-2001
DOI: 10.1088/0031-9155/46/11/312
Abstract: Changes in the linear attenuation coefficient of polymer gel dosimeters post-irradiation enable the imaging of dose distributions by x-ray computed tomography (CT). Various compositions of polymer gel dosimeters manufactured from acrylamide (AA), and N,N'-methylene-bis-acrylamide (BIS) comonomers and gelatin or agarose gelling agents were investigated. This work shows that increasing the comonomer concentration increases the CT-dose sensitivity of the polymer gel dosimeter. This can be further increased by replacing gelatin with agarose. Varying the gelatin concentration however does not significantly change the CT-dose sensitivity. Among the compositions studied, dose resolution (D(delta)95%) was found to be optimal for polymer gel dosimeters comprising 5% gelatin, 3% AA, 3% BIS and 89% water.
Publisher: Wiley
Date: 26-03-2010
DOI: 10.1118/1.3355873
Abstract: The component modules in the standard BEAMnrc istribution may appear to be insufficient to model micro-multileaf collimators that have trifaceted leaf ends and complex leaf profiles. This note indicates, however, that accurate Monte Carlo simulations of radiotherapy beams defined by a complex collimation device can be completed using BEAMnrc's standard VARMLC component module. That this simple collimator model can produce spatially and dosimetrically accurate microcollimated fields is illustrated using comparisons with ion chamber and film measurements of the dose deposited by square and irregular fields incident on planar, homogeneous water phantoms. Monte Carlo dose calculations for on-axis and off-axis fields are shown to produce good agreement with experimental values, even on close examination of the penumbrae. The use of a VARMLC model of the micro-multileaf collimator, along with a commissioned model of the associated linear accelerator, is therefore recommended as an alternative to the development or use of in-house or third-party component modules for simulating stereotactic radiotherapy and radiosurgery treatments. Simulation parameters for the VARMLC model are provided which should allow other researchers to adapt and use this model to study clinical stereotactic radiotherapy treatments.
Publisher: Springer International Publishing
Date: 2015
Publisher: Radiation Research Society
Date: 2009
DOI: 10.1667/RR1438.1
Publisher: IOP Publishing
Date: 10-09-2004
DOI: 10.1088/0031-9155/49/19/N01
Abstract: A single large dose of megavoltage x-rays delivered through a grid is currently being utilized by some centres for palliative radiotherapy treatments of large tumours. In this note, we investigate the dosimetry of grid therapy using two-dimensional film dosimetry and three-dimensional gel dosimetry. It is shown that the radiation dose is attenuated more rapidly with depth in a grid field than an open field, and that even shielded regions receive approximately 25% of the dose to the unshielded areas.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2009
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2005
End Date: 2008
Funder: Australian Research Council
View Funded ActivityStart Date: 2011
End Date: 2013
Funder: Wesley Research Institute
View Funded ActivityStart Date: 2010
End Date: 2014
Funder: Cancer Australia
View Funded ActivityStart Date: 2009
End Date: 2010
Funder: Wesley Research Institute
View Funded ActivityStart Date: 12-2005
End Date: 06-2009
Amount: $250,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 04-2011
End Date: 12-2015
Amount: $305,000.00
Funder: Australian Research Council
View Funded Activity