ORCID Profile
0000-0002-8797-9586
Current Organisation
Royal Brisbane and Women's Hospital
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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: Springer Berlin Heidelberg
Date: 2013
Publisher: Springer Singapore
Date: 30-05-2019
Publisher: Wiley
Date: 12-08-2011
DOI: 10.1118/1.3611044
Abstract: In this paper, the authors assess the accuracy of the Brainlab ExacTrac system for frameless intracranial stereotactic treatments in clinical practice. They recorded couch angle and image fusion results (comprising lateral, longitudinal, and vertical shifts, and rotation corrections about these axes) for 109 stereotactic radiosurgery and 166 stereotactic radiotherapy patient treatments. Frameless stereotactic treatments involve iterative 6D image fusion corrections applied until the results conform to customizable pass criteria, theirs being 0.7 mm and 0.5° for each axis. The planning CT slice thickness was 1.25 mm. It has been reported in the literature that the CT slices' thickness impacts the accuracy of localization to bony anatomy. The principle of invariance with respect to patient orientation was used to determine spatial accuracy. The data for radiosurgery comprised 927 image pairs, of which 532 passed (pass ratio of 57.4%). The data for radiotherapy comprised 15983 image pairs, of which 10 050 passed (pass ratio of 62.9%). For stereotactic radiotherapy, the combined uncertainty of ExacTrac calibration, image fusion, and intrafraction motion was (95% confidence interval) 0.290-0.302 and 0.306-0.319 mm in the longitudinal and lateral axes, respectively. The combined uncertainty of image fusion and intrafraction motion in the anterior-posterior coordinates was 0.174-0.182 mm. For stereotactic radiosurgery, the equivalent ranges are 0.323-0.393, 0.337-0.409, and 0.231-0.281 mm. The overall spatial accuracy was 1.24 mm for stereotactic radiotherapy (SRT) and 1.35 mm for stereotactic radiosurgery (SRS). The ExacTrac intracranial frameless stereotactic system spatial accuracy is adequate for clinical practice, and with the same pass criteria, SRT is more accurate than SRS. They now use frameless stereotaxy exclusively at their center.
Publisher: Springer Science and Business Media LLC
Date: 20-08-2018
DOI: 10.1007/S13246-018-0673-4
Abstract: The use of a non-water-equivalent personalised mould for gynaecological brachytherapy treatments can result in a substantial dose reduction at the treatment site, compared to calculated dose, in lieu of a dose calculation algorithm capable of modelling non-water-equivalent materials. This study describes the characterisation of the radiological properties of a brachytherapy applicator moulding material. Simple line source correction factors for an
Publisher: Elsevier BV
Date: 02-2014
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: Elsevier BV
Date: 03-2015
DOI: 10.1016/J.BRACHY.2014.10.004
Abstract: Patients with cervical and vaginal cancer sometimes have a less straightforward approach for choice of brachytherapy treatment owing to the tumor's location and clinical presentation. The staff at Royal Brisbane & Women's Hospital in Queensland, Australia, is trying to solve this problem by the use of an old technique in a new approach called vaginal molds. With a patient-specific vaginal mold, the appearance of the applicator and the dose distribution can be customized to provide an optimal treatment for each patient. The technique used at the Royal Brisbane & Women's Hospital uses a flexible two-part putty, moulded to the shape of the vagina, in which standard catheters (flexible implant tubes) are incorporated, in a pattern designed to permit a dose distribution more conformal to the target volume. The presented technique is efficient and improves the accuracy of a homogeneous target cover and sparing of organs at risk for vaginal mold brachytherapy treatments at our institution. This technique offers a customizable option when traditional cylindrical- or dome-type applicators cannot be used, or provide inadequate dose coverage. Molds to match the patient anatomy can be created quickly, while allowing flexibility in positioning of catheters to achieve the desired dose distribution.
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: Wiley
Date: 21-07-2017
DOI: 10.1002/ACM2.12136
Publisher: Springer Science and Business Media LLC
Date: 02-2015
DOI: 10.1007/S13246-015-0331-Z
Abstract: Exit-detector data from helical radiation therapy have been studied extensively for delivery verification and dose reconstruction. Since the same radiation source is used for both imaging and treatment, this work investigates the possibility of utilising exit-detector raw data for imaging purposes. This gives rise to potential clinical applications such as retrospective daily setup verification and inter-fractional setup error detection. The exit-detector raw data were acquired and independently analysed using Python programming language. The raw data were extracted from the treatment machine's onboard computer, and converted into 2D array files. The contours of objects (phantom or patient) were acquired by applying a logarithmic function to the ratio of two sinograms, one with the object in the beam and one without. The setup variation between any two treatment deliveries can be detected by applying the same function to their corresponding exit-detector sinograms. The contour of the object was well defined by the secondary radiation from the treatment beam and validated with the imaging beam, although no internal structures were discernible due to the interference from the primary radiation. The sensitivity of the setup variation detection was down to 2 mm, which was mainly limited by the resolution of the exit-detector itself. The exit-detector data from treatment procedures contain valuable photon exit fluence maps which can be utilised for contour definition and verification of patient alignment without reconstruction.
Publisher: MDPI AG
Date: 18-08-2021
DOI: 10.3390/JMSE9080888
Abstract: The accurate classification of reservoir recovery factor is d ened by irregularities such as noisy and high-dimensional features associated with the reservoir measurements or characterization. These irregularities, especially a larger number of features, make it difficult to perform accurate classification of reservoir recovery factor, as the generated reservoir features are usually heterogeneous. Consequently, it is imperative to select relevant reservoir features while preserving or lifying reservoir recovery accuracy. This phenomenon can be treated as a multi-objective optimization problem, since there are two conflicting objectives: minimizing the number of measurements and preserving high recovery classification accuracy. In this study, wrapper-based multi-objective feature selection approaches are proposed to estimate the set of Pareto optimal solutions that represents the optimum trade-off between these two objectives. Specifically, three multi-objective optimization algorithms—Non-dominated Sorting Genetic Algorithm II (NSGA-II), Multi-Objective Grey Wolf Optimizer (MOGWO) and Multi-Objective Particle Swarm Optimization (MOPSO)—are investigated in selecting relevant features from the reservoir dataset. To the best of our knowledge, this is the first time multi-objective optimization has been used for reservoir recovery factor classification. The Artificial Neural Network (ANN) classification algorithm is used to evaluate the selected reservoir features. Findings from the experimental results show that the proposed MOGWO-ANN outperforms the other two approaches (MOPSO and NSGA-II) in terms of producing non-dominated solutions with a small subset of features and reduced classification error rate.
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: 11-2014
DOI: 10.1016/J.IJROBP.2014.05.052
Abstract: To characterize and compare the components of out-of-field dose for 18-MV intensity modulated radiation therapy (IMRT) versus 3-dimensional conformal radiation therapy (3D-CRT) and their 6-MV counterparts and consider implications for second cancer induction. Comparable plans for each technique/energy were delivered to a water phantom with a sloping wall under full scatter conditions with field edge abutting but outside the bath to prevent internal hantom scatter and with shielding below the linear accelerator head to attenuate head leakage. Neutron measurements were obtained from published studies. Eighteen-megavolt IMRT produces 1.7 times more out-of-field scatter than 18-MV 3D-CRT. In absolute terms, however, differences are just approximately 0.1% of central axis dose. Eighteen-megavolt IMRT reduces internal atient scatter by 13%, but collimator scatter (C) is 2.6 times greater than 18-MV 3D-CRT. Head leakage (L) is minimal. Increased out-of-field photon scatter from 18-MV IMRT carries out-of-field second cancer risks of approximately 0.2% over and above the 0.4% from 18-MV 3D-CRT. Greater photoneutron dose from 18-MV IMRT may result in further maximal, absolute increased risk to peripheral tissue of approximately 1.2% over 18-MV 3D-CRT. Out-of-field photon scatter remains comparable for the same modality irrespective of beam energy. Machine scatter (C+L) from 18 versus 6 MV is 1.2 times higher for IMRT and 1.8 times for 3D-CRT. It is 4 times higher for 6-MV IMRT versus 3D-CRT. Reduction in internal scatter with 18 MV versus 6 MV is 27% for 3D-CRT and 29% for IMRT. Compared with 6-MV 3D-CRT, 18-MV IMRT increases out-of-field second cancer risk by 0.2% from photons and adds 0.28-2.2% from neutrons. Out-of-field photon dose seems to be independent of beam energy for both techniques. Eighteen-megavolt IMRT increases out-of-field scatter 1.7-fold over 3D-CRT because of greater collimator scatter despite reducing internal atient scatter. Out-of-field carcinogenic risk is thus increased (but improved in-field dose conformity may offset this). Potentially increased carcinogenic risk should be weighed against any benefit 18-MV IMRT may provide.
Publisher: Springer Science and Business Media LLC
Date: 07-12-2014
DOI: 10.1007/S13246-014-0317-2
Abstract: To investigate how the dwell time deviation constraint (DTDC) parameter, applied to inverse planning by simulated annealing (IPSA) optimisation limits large dwell times from occurring in each catheter and to characterise the effect on the resulting dosimetry for prostate high dose rate (HDR) brachytherapy treatment plans. An unconstrained IPSA optimised treatment plan, using the Oncentra Brachytherapy treatment planning system (version 4.3, Nucletron an Elekta company, Elekta AB, Stockholm, Sweden), was generated for 20 consecutive HDR prostate brachytherapy patients, with the DTDC set to zero. Successive constrained optimisation plans were also created for each patient by increasing the DTDC parameter by 0.2, up to a maximum value of 1.0. We defined a "plan modulation index", to characterise the change of dwell time modulation as the DTDC parameter was increased. We calculated the dose volume histogram indices for the PTV (D90, V100, V150, V200%) and urethra (D10%) to characterise the effect on the resulting dosimetry. The average PTV D90% decreases as the DTDC is applied, on average by only 1.5 %, for a DTDC = 0.4. The measures of high dose regions in the PTV, V150 and V200%, increase on average by less than 5 and 2 % respectively. The net effect of DTDC on the modulation of dwell times has been characterised by the introduction of the plan modulation index. DTDC applied during IPSA optimisation of HDR prostate brachytherapy plans reduce the occurrence of large isolated dwell times within in idual catheters. The mechanism by which DTDC works has been described and its effect on the modulation of dwell times has been characterised. The authors recommend using a DTDC parameter no greater than 0.4 to obtain a plan with dwell time modulation comparable to a geometric optimised plan. This yielded on average a 1.5 % decrease in PTV coverage and an acceptable increase in V150%, without compromising the urethral dose.
Publisher: Elsevier BV
Date: 12-2011
DOI: 10.1016/J.IJROBP.2010.08.008
Abstract: To investigate differences in scatter and leakage between 6-MV intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3DCRT) to describe the relative contributions of internal patient scatter, collimator scatter, and head leakage and to discuss implications for second cancer induction. Dose was measured at increasing distances from the field edge in a water bath with a sloping wall (1) under full scatter conditions, (2) with the field edge abutting but outside the bath to prevent internal (water) scatter, and (3) with the beam aperture plugged to reflect leakage only. Internal patient scatter from IMRT is 11% lower than 3DCRT, but collimator scatter and head leakage are five and three times higher, respectively. Ultimately, total scattered dose is 80% higher with IMRT however this difference is small in absolute terms, being 0.14% of prescribed dose. Secondary dose from 3DCRT is mostly due to internal patient scatter, which contributes 70% of the total and predominates until 25 cm from the field edge. For IMRT, however, machine scatter/leakage is the dominant source, contributing 65% of the secondary dose. Internal scatter predominates for just the first 10 cm from field edge, collimator scatter for the next 10 cm, and head leakage thereafter. Out-of-field dose is 80% higher with IMRT, but differences are tiny in absolute terms. Reductions in internal patient scatter with IMRT are outweighed by increased machine scatter and leakage, at least for small fields. Reductions from IMRT in dose to tissues within the portals and in internal scatter, which predominates close to the field edge, means that calculations based solely on dose to distant tissues may overestimate carcinogenic risks.
Publisher: Wiley
Date: 05-2015
Abstract: The purpose of this study was to investigate the impact of a dose control system (DCS) servo installed on two fully commissioned TomoTherapy Hi·Art II treatment units. This servo is designed to actively adjust machine parameters to control the output variation of a tomotherapy unit to within ± 0.5% of the nominal dose rate. Machine output, dose rate, and patient-specific quality assurance data were retrospectively analyzed for periods prior to and following the installation of the servo system. Quality assurance tests indicate a reduction in the rotational variation of the output during a procedure, where the peak-to-peak litude of the variation was ± 1.30 prior to DCS and equal to ± 0.4 with DCS. Comparing two tomotherapy unit static outputs over four years the percentage error was 1.05% ± 0.7% and -0.4% ± 0.66% and, once DCS was installed, was reduced to -0.22% ± 0.29% and -0.08% ± 0.16%. The results of the quality assurance tests indicate that the dose control system reduced the output variation of each machine for both static and rotational delivery, leading to an improvement in the overall performance of the machine and providing greater certainty in treatment delivery.
Publisher: VM Media SP. zo.o VM Group SK
Date: 2020
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.
No related grants have been discovered for Craig Lancaster.