ORCID Profile
0000-0002-5023-1558
Current Organisation
Princess Alexandra Hospital
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Publisher: Elsevier BV
Date: 03-2015
DOI: 10.1016/J.EJMP.2015.01.002
Abstract: To construct a method and software to track gold seed implants in prostate and lung patients undergoing radiotherapy using CBCT image projections. A mathematical model was developed in the MatLab (Mathworks, Natick, USA) environment which uses a combination of discreet cosine transforms and filtering to enhance several edge detection methods for identifying and tracking gold seed fiducial markers in images obtained from Varian (Varian Medical Systems, Palo Alto, USA) and Elekta (Kungstensgatan, Sweden) CBCT projections. Organ motion was captured for 16 prostate patients and 1 lung patient. Image enhancement and edge detection is capable of automatically tracking markers for up to 98% (Varian) and 79% (Elekta) of CBCT projections for prostate and lung markers however inclusion of excessive bony anatomy (LT and RT LAT) inhibit the ability of the model to accurate determine marker location.
Publisher: Korean Society for Therapeutic Radiology and Oncology
Date: 30-06-2021
Publisher: Wiley
Date: 08-11-2016
DOI: 10.1002/JMRS.186
Publisher: Medknow
Date: 2021
Publisher: Baishideng Publishing Group Inc.
Date: 2017
Publisher: IOP Publishing
Date: 15-03-2022
Abstract: Purpose . The aim of this study was to assess the feasibility of the development and training of a deep learning object detection model for automating the assessment of fiducial marker migration and tracking of the prostate in radiotherapy patients. Methods and Materials . A fiducial marker detection model was trained on the YOLO v2 detection framework using approximately 20,000 pelvis kV projection images with fiducial markers labelled. The ability of the trained model to detect marker positions was validated by tracking the motion of markers in a respiratory phantom and comparing detection data with the expected displacement from a reference position. Marker migration was then assessed in 14 prostate radiotherapy patients using the detector for comparison with previously conducted studies. This was done by determining variations in intermarker distance between the first and subsequent fractions in each patient. Results . On completion of training, a detection model was developed that operated at a 96% detection efficacy and with a root mean square error of 0.3 pixels. By determining the displacement from a reference position in a respiratory phantom, experimentally and with the detector it was found that the detector was able to compute displacements with a mean accuracy of 97.8% when compared to the actual values. Interfraction marker migration was measured in 14 patients and the average and maximum ± standard deviation marker migration were found to be 2.0 ± 0.9 mm and 2.3 ± 0.9 mm , respectively. Conclusion . This study demonstrates the benefits of pairing deep learning object detection, and image-guided radiotherapy and how a workflow to automate the assessment of organ motion and seed migration during prostate radiotherapy can be developed. The high detection efficacy and low error make evident the advantages of using a pre-trained model to automate the assessment of the target volume positional variation and the migration of fiducial markers between fractions.
Publisher: VM Media SP. zo.o VM Group SK
Date: 07-2019
Publisher: IOP Publishing
Date: 11-2022
Abstract: Aims . To explore the efficacy of two different approaches to train a Fully Convolutional Neural Network (FCNN) with Graphical Processing Unit (GPU) memory limitations and investigate if pre-trained two-dimensional weights can be transferred into a three-dimensional model for the purpose of brain tumour segmentation. Materials and methods . Models were developed in Python using TensorFlow and Keras. T1 contrast-enhanced MRI scans and associated contouring data from 104 patients were used to train and validate the model. The data was resized to one-quarter of its original resolution, and the original data was also split into four quarters for comparison to fit within GPU limitations. Transferred weights from a two-dimensional VGG16 model trained on ImageNet were transformed into three dimensions for comparison with randomly generated initial weights. Results . Resizing the data produced superior dice similarity coefficients with fewer false positives than quartering the data. Quartering the data yielded a superior sensitivity. Transforming and transferring two-dimensional weights was not able to consistently produce improvement in training or final metrics. Conclusion . For segmentation of brain tumours, resizing the data results in better performance than quartering the data. For the model and approaches used in this report, transferring weights were not able to demonstrate any benefit.
Publisher: Informa UK Limited
Date: 09-2018
DOI: 10.2147/IJN.S174624
Publisher: IOP Publishing
Date: 27-07-2023
Abstract: The quality of organ volume delineation significantly influences the efficacy of radiotherapy treatment for breast cancer patients. This study introduces a novel method for auto-segmentation of the breasts, lungs and heart. The proposed pipeline leverages a multi-class 3D U-Net with a pre-trained ResNet(2+1)D-18 encoder branch, cascaded with a 2D PatchGAN mask correction model for each class. This approach requires a single 3D model, providing a relatively efficient solution. The models were trained and evaluated on 70 thoracic DICOM datasets belonging to breast cancer patients. The evaluation demonstrated state-of-the-art segmentation performance, with mean Dice similarity coefficient values ranging from 0.89 to 0.98, Hausdorff distance values ranging from 2.25 to 8.68 mm, and mean surface distance values ranging from 0.62 to 2.79 mm. These results underscore the pipeline’s potential to enhance breast cancer diagnosis and treatment strategies, with possible applications in other medical sectors utilizing auto-segmentation.
Publisher: Springer Science and Business Media LLC
Date: 11-07-2022
DOI: 10.1007/S13246-022-01155-X
Abstract: Optically stimulated luminescence dosimetry is a relatively recent field of in-vivo dosimetry in clinical radiotherapy, developing over the last 20 years. As a pilot study, this paper presents a direct comparison between the sensitivity variance with use, stability of measurement and linearity of the current clinical standard Al 2 O 3 :C and a potential alternative, beryllium oxide. A set of ten optically stimulated luminescence dosimeters (OSLD), including five of each type, were used simultaneously and irradiated on a Versa HD linear accelerator. Having similar sensitivity, while Al 2 O 3 :C showed a relatively stable signal response from initial use, BeO was found to have a higher response to the same dose. However, BeO displayed a strong exponential decline from initial signal response following a model of $$Respons{e}_{BeO}=(0.55\\pm 0.05){e}^{-\\left(0.40\\pm 0.05\\right)x}+(0.54\\pm 0.01)$$ R e s p o n s e BeO = ( 0.55 ± 0.05 ) e - 0.40 ± 0.05 x + ( 0.54 ± 0.01 ) , reaching stability after approximately 10 irradiation cycles. BeO was shown to have potentially higher accuracy than Al 2 O 3 :C, with less variation between in idual doses. Both OSLD showed good linearity between 0.2–5.0 Gy. Between these bounds, Al 2 O 3 :C demonstrated a strong linear response following the trend $$Dose_{Al_{2}O_{3}, group(adj)}=(1.00\\pm 0.09)x-(0.02\\pm 0.04)\\,{\\text{Gy}}$$ D o s e A l 2 O 3 , g r o u p ( a d j ) = ( 1.00 ± 0.09 ) x - ( 0.02 ± 0.04 ) Gy , however beyond this showed deviation from linearity, resulting in a measured dose of $$12.0\\pm 0.2$$ 12.0 ± 0.2 Gy at 10.0 Gy dose delivery. BeO showed strong linearity across the full examined range of 0.2–10.0 Gy with following a model of $$Dos{e}_{BeO, ind}=(0.98\\pm 0.01)x+(0.04\\pm 0.01)$$ D o s e B e O , i n d = ( 0.98 ± 0.01 ) x + ( 0.04 ± 0.01 ) Gy with a recorded dose at 10.0 Gy delivery as $$9.9\\pm 0.1$$ 9.9 ± 0.1 Gy. In conclusion, BeO does show large variance in sensitivity between in idual OSLD and a considerable initial variance and decline in dose–response, however after pre-conditioning and in idual normalisation to offset OSLD specific sensitivity BeO provides not only a viable alternative to Al 2 O 3 :C, but potentially provide higher accuracy, precision and reproducibility for in-vivo dosimetry.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-07-2023
DOI: 10.1126/SCITRANSLMED.ABQ5923
Abstract: Proteomic studies for Alzheimer’s disease (AD) are instrumental in identifying AD pathways but often focus on single tissues and sporadic AD cases. Here, we present a proteomic study analyzing 1305 proteins in brain tissue, cerebrospinal fluid (CSF), and plasma from patients with sporadic AD, TREM2 risk variant carriers, patients with autosomal dominant AD (ADAD), and healthy in iduals. We identified 8 brain, 40 CSF, and 9 plasma proteins that were altered in in iduals with sporadic AD, and we replicated these findings in several external datasets. We identified a proteomic signature that differentiated TREM2 variant carriers from both in iduals with sporadic AD and healthy in iduals. The proteins associated with sporadic AD were also altered in patients with ADAD, but with a greater effect size. Brain-derived proteins associated with ADAD were also replicated in additional CSF s les. Enrichment analyses highlighted several pathways, including those implicated in AD (calcineurin and Apo E), Parkinson’s disease (α-synuclein and LRRK2), and innate immune responses (SHC1, ERK-1, and SPP1). Our findings suggest that combined proteomics across brain tissue, CSF, and plasma can be used to identify markers for sporadic and genetically defined AD.
Publisher: Elsevier BV
Date: 11-2021
DOI: 10.1016/J.ZEMEDI.2021.04.003
Abstract: Dose to the contralateral breast (CLB) from radiotherapy treatment has the potential to induce secondary breast cancer. Electronic tissue compensation (eComp) for breast cancer patients is one of the alternative methods to conventional 3D-conformal radiotherapy that eliminates the use of wedges. Several studies have investigated dose to the CLB using tangential fields involving wedges, intensity-modulated radiation therapy and volumetric modulated arc radiation therapy and various other techniques via treatment planning system calculations, Monte Carlo methods and phantoms. However, there are limited data published in assessing the actual dose received by the CLB from treatment with eComp-based tangential fields. In this study, the CLB dose for patients undergoing tangential field radiotherapy with eComp and enhanced dynamic wedged (standard) tangential fields was measured and compared to assess the CLB dose between the two methods. Measurements were conducted on a randomised trial of 40 patients, 20 of them had undergone standard planning, and the remaining 20 were treated with eComp. The mean surface dose measured with TLDs at 3cm from the medial tangential border for eComp and standard techniques was 10.04±1.37% and 10.14±2.05%, respectively for a prescription dose of 2.65Gy/fraction. The estimated dose at 1cm depth in tissue, measured with the use of perspex domes placed over the TLD at the same location, was 5.12±0.87% and 6.29±2.01% for eComp and standard, respectively. The CLB dose is dependent on the proximity of the medial tangential field edge to the contralateral breast and is patient-specific. The results of this study show that at 1cm depth, eComp technique delivers significantly less dose (p<0.05) to the CLB as compared to standard tangential fields. Furthermore, the surface dose measured for both eComp and standard are comparable indicating that the eComp-based tangential field technique does not contribute any excess dose to CLB when compared to standard tangential fields. The excess relative risk (ERR) for radiation-induced cancers for eComp was found to be 0.08, compared to 0.11 for standard tangential fields.
Publisher: IOP Publishing
Date: 15-03-2021
Abstract: Geometric distortions in magnetic resonance can introduce significant uncertainties into applications such as radiotherapy treatment planning and need to be assessed as part of a comprehensive quality assurance program. We report the design, fabrication, and imaging of a custom 3D printed unibody MR distortion phantom along with quantitative image analysis. Methods : The internal cavity of the phantom is an orthogonal three-dimensional planar lattice, composed of 3 mm diameter rods spaced equidistantly at a 20 mm centre-centre offset repeating along the X, Y, and Z axes. The phantom featured an overall length of 308.5 mm, a width of 246 mm, and a height of 264 mm with lines on the external surface for phantom positioning matched to external lasers. The MR phantom was 3D printed in Nylon-12 using an advancement on traditional selective laser sintering (SLS) (HP Jet Fusion 3D—4200 machine). The phantom was scanned on a Toshiba Aquilion CT scanner to check the integrity of the 3D print and correct for any resultant issues. The phantom was then filled with NiSO 4 solution and scanned on a 3T PET-MR Siemens scanner for selected T1 and T2 sequences, from which distortion vectors were generated and analysed using in-house software written in Python. Results : All deviations of the node positions from the print design were less than 1 mm, with an average displacement of 0.228 mm. The majority of the deviations were smaller than the 0.692 mm pixel size for this dataset. Conclusion : A customised 3D printed MRI-phantom was successfully printed and tested for assessing geometric distortion on MRI scanners. 3D printed phantoms can be considered for clinics wishing to assess geometric distortions under specific conditions, but require resources for design, fabrication, commissioning, and verification.
Publisher: Elsevier BV
Date: 07-2019
Publisher: Elsevier BV
Date: 12-2017
DOI: 10.1016/J.ZEMEDI.2017.05.002
Abstract: This study examines the difference in surface dose between flat and flattening filter free (FFF) photon beams in the context of breast radiotherapy. The surface dose was measured for 6MV, 6MV FFF, 10MV, 10MV FFF and 18MV photon beams using a thin window ionisation chamber for various field sizes. Profiles were acquired to ascertain the change in surface dose off-axis. Out-of-field measurements were included in a clinically representative half beam block tangential breast field. In the field centres of FFF beams the surface dose was found to be increased for small fields and decreased for large fields compared to flat beams. For FFF beams, surface dose was found to decrease off-axis and resulted in lower surface dose out-of-field compared to flat beams.
Publisher: Korean Society for Therapeutic Radiology and Oncology
Date: 31-12-2020
Publisher: Medknow
Date: 2017
No related grants have been discovered for prabhakar ramachandran.