Shrikant Deshpande - Academia.edu (original) (raw)

Papers by Shrikant Deshpande

Advances in Radiation Oncology, 2021

Purpose This retrospective patient study assessed the consistency of abdominal gas presence throu... more Purpose This retrospective patient study assessed the consistency of abdominal gas presence throughout radiation therapy for patients with upper gastrointestinal cancer and determined the impact of variations in gas volume on the calculated dose distribution of volumetric modulated arc therapy. Methods and Materials Eight patients with pancreatic cancer were included for analysis. A plan library consisting of 3 reference plans per patient (Ref0.0, Ref0.5, and Ref1.0) was created based on planning computed tomography (CT) with density overrides of 0.0, 0.5, and 1.0 applied to gas volumes, respectively. Corresponding cone beam CT (CBCT) data sets were obtained and density overrides were applied to enable fractional dose calculation. Variation in gas volume relative to initial volume determined from CT was assessed. Dose metrics for targets and organs at risk were compared between the accumulated CBCT dose and the planned dose of the 3 reference plans for each patient. Results There wa...

Journal of Medical Radiation Sciences, 2021

As medical imaging specialists we want to provide our patients with the best safest examination w... more As medical imaging specialists we want to provide our patients with the best safest examination we can give them. We need to ensure that they have all the information they need to understand and then consent to their imaging procedure. We can only do this if we put them at the centre of the process. Consent was in the past limited to larger or more complicated procedures. The changing expectations mean we need to change our processes. The conundrum for low-risk procedures is how we do this in a busy X-ray department without compromising the quality of the information and the safety of our patients. Are allied health students sufficiently prepared to deal with intimate partner violence? Yifan (Yvonne) Gao, Courtney Thomas Monash University, Clayton, Australia

Australasian physical & engineering sciences in medicine, Jan 12, 2017

A survey of radiation oncology medical physics departments across Australia and New Zealand was c... more A survey of radiation oncology medical physics departments across Australia and New Zealand was conducted to assess the usage, commissioning and quality assurance of modulated radiotherapy techniques such as IMRT and VMAT. Survey responses were collected in April-May 2015 to snapshot current practice and historical implementation. The survey asked 142 questions, and is the most detailed survey of its kind published to date. Analysis of results at overall department level, as well as sub-analysis for different equipment and techniques in use, was performed. Results show a high prevalence of IMRT and VMAT in use, and demonstrate the large heterogeneity in clinical practice and experience across the region.

Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), 2017

Develop a framework to characterize helical TomoTherapy (HT) machine delivery errors and their cl... more Develop a framework to characterize helical TomoTherapy (HT) machine delivery errors and their clinical significance. Ten nasopharynx HT plans were edited to introduce errors in Jaw width (JW), couch speed (CS), gantry period (GP), gantry start position (GSP), multi leaf collimator leaf open times (MLC LOT). In case of MLC LOT only, both systematic and random delivery errors were investigated. Each error type was simulated independently for a range of magnitudes. Dose distributions for the clinical reference plans and the error simulated plans were compared to establish the magnitude for each error type which resulted in a change in clinical tolerance, defined as 5% variation in D95 of PTV70, D0.1cc of spinal cord, D0.1cc of brainstem and the smallest value of either a 10% or 3.6Gy dose variation in mean parotid dose. Dose variation from systematic delivery errors in JW ±0.5mm, CS ranges between -1% to 1.5%, GP ±1s, GSP ranges between -2(0) to 2.5(0) and MLC LOT random error up to 2...

Radiotherapy and Oncology, 2015

Results: Whereas for machines younger than 10 years agreement between measured and stated dose wa... more Results: Whereas for machines younger than 10 years agreement between measured and stated dose was 90% overall, for those over 30 years old agreement dropped to 70%. However, this picture varied with region. Linac dosimetry was always better than 60 Co and multi-machine centres generally performed better than single machine institutions. We interpret this latter observation as a reflection of a more substantial physics infrastructure in larger centres. The data suggest virtually no dependence on the time elapsed since the last dosimetry system calibration at least out to 10 years. Second or subsequent participation in audits reflected higher quality dosimetry (85% of results within the XX's acceptance criterion) than the first audit (77%). The use of N D,w based dosimetry protocols resulted in more accurate dosimetry than the use of the older N k or N x protocols (95%, 92% and 79% agreement respectively). Conclusions: Clearly, over the 45 years that the XX has accumulated these TLD data, practice has changed both in institutions and at the XX's Dosimetry Laboratory. However, it is possible to draw some general conclusions from the analysis. Higher quality dosimetry is generally associated with younger machines, linacs as opposed to 60 Co, centres with more than one machine, prior experience with the XX's audit programme and the use of an N D,w based protocol.

Physics in Medicine and Biology

Medical Physics

The aim of this study was to validate the accuracy of an exit detector-based dose reconstruction ... more The aim of this study was to validate the accuracy of an exit detector-based dose reconstruction tool for helical tomotherapy (HT) delivery quality assurance (DQA). Exit detector-based DQA tool was developed for patient-specific HT treatment verification. The tool performs a dose reconstruction on the planning image using the sinogram measured by the HT exit detector with no objects in the beam (i.e., static couch), and compares the reconstructed dose to the planned dose. Vendor supplied (three "TomoPhant") plans with a cylindrical solid water ("cheese") phantom were used for validation. Each "TomoPhant" plan was modified with intentional multileaf collimator leaf open time (MLC LOT) errors to assess the sensitivity and robustness of this tool. Four scenarios were tested; leaf 32 was "stuck open," leaf 42 was "stuck open," random leaf LOT was closed first by mean values of 2% and then 4%. A static couch DQA procedure was then run five times (once with the unmodified sinogram and four times with modified sinograms) for each of the three "TomoPhant" treatment plans. First, the original optimized delivery plan was compared with the original machine agnostic delivery plan, then the original optimized plans with a known modification applied (intentional MLC LOT error) were compared to the corresponding error plan exit detector measurements. An absolute dose comparison between calculated and ion chamber (A1SL, Standard Imaging, Inc., WI, USA) measured dose was performed for the unmodified "TomoPhant" plans. A 3D gamma evaluation (2%/2 mm global) was performed by comparing the planned dose ("original planned dose" for unmodified plans and "adjusted planned dose" for each intentional error) to exit detector-reconstructed dose for all three "Tomophant" plans. Finally, DQA for 119 clinical (treatment length <25 cm) and three cranio-spinal irradiation (CSI) plans were measured with both the ArcCHECK phantom (Sun Nuclear Corp., Melbourne, FL, USA) and the exit detector DQA tool to assess the time required for DQA and similarity between two methods. The measured ion chamber dose agreed to within 1.5% of the reconstructed dose computed by the exit detector DQA tool on a cheese phantom for all unmodified "Tomophant" plans. Excellent agreement in gamma pass rate (>95%) was observed between the planned and reconstructed dose for all "Tomophant" plans considered using the tool. The gamma pass rate from 119 clinical plan DQA measurements was 94.9% ± 1.5% and 91.9% ± 4.37% for the exit detector DQA tool and ArcCHECK phantom measurements (P = 0.81), respectively. For the clinical plans (treatment length <25 cm), the average time required to perform DQA was 24.7 ± 3.5 and 39.5 ± 4.5 min using the exit detector QA tool and ArcCHECK phantom, respectively, whereas the average time required for the 3 CSI treatments was 35 ± 3.5 and 90 ± 5.2 min, respectively. The exit detector tool has been demonstrated to be faster for performing the DQA with equivalent sensitivity for detecting MLC LOT errors relative to a conventional phantom-based QA method. In addition, comprehensive MLC performance evaluation and features of reconstructed dose provide additional insight into understanding DQA failures and the clinical relevance of DQA results.

Journal of applied clinical medical physics / American College of Medical Physics, Jan 8, 2015

Verification of dose to the anterior rectal wall in helical tomotherapy to the prostate is import... more Verification of dose to the anterior rectal wall in helical tomotherapy to the prostate is important due to the close proximity of the rectal wall to the treatment field. The steep dose gradient makes these measurements challenging. A phantom-based study was completed, aimed at developing a system for measurement of anterior rectal wall doses during hypofractionated prostate stereotactic body radiotherapy (SBRT) utilizing tomotherapy delivery. An array of four dual MOSkinTM dosimeters, spaced 1 cm apart, was placed on a replica Rectafix® immobilization spacer device. This Perspex probe is a more rigid alternative to rectal balloons, to improve geometric reproducibility. The doses at each point were measured in real time and compared to doses calculated by the treatment planning system (TPS). Additionally, distance-to-agreement (DTA) measurements were acquired to assist in the comparison of measured and predicted doses. All dual MOSkin detectors measured dose to within ± 5% of the TP...

Medical Physics, 2015

ABSTRACT This study evaluated the plan quality and dose delivery accuracy of stereotactic body ra... more ABSTRACT This study evaluated the plan quality and dose delivery accuracy of stereotactic body radiotherapy (SBRT) helical Tomotherapy (HT) treatments for lung cancer. Results were compared with those previously reported by our group for flattening filter (FF) and flattening filter free (FFF) VMAT treatments. This work forms part of an ongoing multicentre and multisystem planning and dosimetry audit on FFF beams for lung SBRT. CT datasets and DICOM RT structures delineating the target volume and organs at risk for 6 lung cancer patients were selected. Treatment plans were generated using the HT treatment planning system. Tumour locations were classified as near rib, near bronchial tree or in free lung with prescribed doses of 48Gy/4fr, 50Gy/5fr and 54Gy/3fr respectively. Dose constraints were specified by a modified RTOG0915 protocol used for an Australian SBRT phase II trial. Plan quality was evaluated using mean PTV dose, PTV volume receiving 100% of the prescribed dose (V100%), target conformity (CI=VD100%/VPTV) and low dose spillage (LDS=VD50%/VPTV). Planned dose distributions were compared to those measured using an ArcCheck phantom. Delivery accuracy was evaluated using a gamma-index pass rate of 95% with 3% (of max dose) and 3mm criteria. Treatment plans for all patients were clinically acceptable in terms of quality and accuracy of dose delivery. The following DVH metrics are reported as averages (SD) of all plans investigated: mean PTV dose was 115.3(2.4)% of prescription, V100% was 98.8(0.9)%, CI was 1.14(0.03) and LDS was 5.02(0.37). The plans had an average gamma-index passing rate of 99.3(1.3)%. The results reported in this study for HT agree within 1 SD to those previously published by our group for VMAT FF and FFF lung SBRT treatments. This suggests that HT delivers lung SBRT treatments of comparable quality and delivery accuracy as VMAT using both FF and FFF beams.

Medical physics, 2015

To test the feasibility of a dual detector concept for comprehensive verification of external bea... more To test the feasibility of a dual detector concept for comprehensive verification of external beam radiotherapy. Specifically, the authors test the hypothesis that a portal imaging device coupled to a 2D dosimeter provides a system capable of simultaneous imaging and dose verification, and that the presence of each device does not significantly detract from the performance of the other. The dual detector configuration comprised of a standard radiotherapy electronic portal imaging device (EPID) positioned directly on top of an ionization-chamber array (ICA) with 2 cm solid water buildup material (between EPID and ICA) and 5 cm solid backscatter material. The dose response characteristics of the ICA and the imaging performance of the EPID in the dual detector configuration were compared to the performance in their respective reference clinical configurations. The reference clinical configurations were 6 cm solid water buildup material, an ICA, and 5 cm solid water backscatter material...

Journal of applied clinical medical physics / American College of Medical Physics, Jan 8, 2014

The purpose of this study was to investigate the dose response of amorphous silicon (a-Si) electr... more The purpose of this study was to investigate the dose response of amorphous silicon (a-Si) electronic portal imaging devices (EPIDs) under different acquisi- tion settings for both open jaw defined fields and segmented intensity-modulated radiation therapy (IMRT) fields. Four different EPIDs were used. Two Siemens and one Elekta plus a standalone Perkin Elmer research EPID. Each was operated with different acquisition systems and settings. Dose response linearity was measured for open static jaw defined fields and 'simple' segmented IMRT fields for a range of equipment and system settings. Six 'simple' segmented IMRT fields were used. The segments of each IMRT field were fixed at 10 × 10 cm2 field size with equal MU per segment, each field having a total of 20 MU. Simultaneous measurements with an ionization chamber array (ICA) and EPID were performed to separate beam and detector response characteristics. Three different pixel calibration meth- ods were demonstrated...

PURPOSE Most of the logistical problems associated with BCT relate to the protracted course of ex... more PURPOSE Most of the logistical problems associated with BCT relate to the protracted course of external beam RT delivered to the whole breast over 5 to 7 weeks. The rationale for this study is based upon two principles. First, higher doses of XRT are given to the tumor bed in an attempt to control residual small foci of cancer that may be left behind after excision alone. Second, the majority of recurrences in the breast of patients who did not receive XRT occurred at or in the area of the tumor bed (within 2 cms). Thus, it would appear that XRT after tumor excision exerts its maximal effect upon reducing breast cancer recurrence at or near the tumor site. Limited volumes allow for treatment on an accelerated schedule. The doses delivered to surrounding organs can possibly be reduced using 3DCRT.OBJECTIVES: This study will evaluate the technical feasibility and reproducibility, cosmetic results, complication rates, and local control rate of 3DCRT confined to the region of the lumpec...

Journal of Physics: Conference Series, 2015

Medical Physics, 2012

Purpose: Current model electronic portal imaging devices (EPIDs) used in radiotherapy are optimis... more Purpose: Current model electronic portal imaging devices (EPIDs) used in radiotherapy are optimised for imaging but problematic for accurate dosimetry. The aim of this project is to develop a new EPID capable of simultaneous imaging and water equivalent dosimetry. This work reports our first experimental results. Methods: A prototype device based on a segmented plastic scintillator (SegmentedPS) was developed. The prototype device was tested in comparison with three other detector configurations, all utilising the same a-Si ...

Medical Physics, 2013

Standard amorphous silicon electronic portal imaging devices (a-Si EPIDs) are x-ray imagers used ... more Standard amorphous silicon electronic portal imaging devices (a-Si EPIDs) are x-ray imagers used frequently in radiotherapy that indirectly detect incident x-rays using a metal plate and phosphor screen. These detectors may also be used as two-dimensional dosimeters; however, they have a well-characterized nonwater-equivalent dosimetric response. Plastic scintillating (PS) fibers, on the other hand, have been shown to respond in a water-equivalent manner to x-rays in the energy range typically encountered during radiotherapy. In this study, the authors report on the first experimental measurements taken with a novel prototype PS a-Si EPID developed for the purpose of performing simultaneous imaging and dosimetry in radiotherapy. This prototype employs an array of PS fibers in place of the standard metal plate and phosphor screen. The imaging performance and dosimetric response of the prototype EPID were evaluated experimentally and compared to that of the standard EPID. Clinical 6 MV photon beams were used to first measure the detector sensitivity, linearity of dose response, and pixel noise characteristics of the prototype and standard EPIDs. Second, the dosimetric response of each EPID was evaluated relative to a reference water-equivalent dosimeter by measuring the off-axis and field size response in a nontransit configuration, along with the off-axis, field size, and transmission response in a transit configuration using solid water blocks. Finally, the imaging performance of the prototype and standard EPIDs was evaluated quantitatively by using an image quality phantom to measure the contrast to noise ratio (CNR) and spatial resolution of images acquired with each detector, and qualitatively by using an anthropomorphic phantom to acquire images representative of human anatomy. The prototype EPID&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s sensitivity was 0.37 times that of the standard EPID. Both EPIDs exhibited responses that were linear with delivered dose over a range of 1-100 monitor units. Over this range, the prototype and standard EPID central axis responses agreed to within 1.6%. Images taken with the prototype EPID were noisier than those taken with the standard EPID, with fractional uncertainties of 0.2% and 0.05% within the central 1 cm(2), respectively. For all dosimetry measurements, the prototype EPID exhibited a near water-equivalent response whereas the standard EPID did not. The CNR and spatial resolution of images taken with the standard EPID were greater than those taken with the prototype EPID. A prototype EPID employing an array of PS fibers has been developed and the first experimental measurements are reported. The prototype EPID demonstrated a much morewater-equivalent dose response than the standard EPID. While the imaging performance of the standard EPID was superior to that of the prototype, the prototype EPID has many design characteristics that may be optimized to improve imaging performance. This investigation demonstrates the feasibility of a new detector design for simultaneous imaging and dosimetry treatment verification in radiotherapy.