bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐BRE‐10: Methods to Simulate and Measure the Attenuation for Modeling a Couch Top with Rails for FFF Treatment Delivery On the Varian Edge Linac
Authors: Gulam M , Gardner S , Zhao B , Snyder K , Song K , Li H , Kearns W , Gordon J , Wen N , Chetty I 
Published: July 2014

Purpose:To measure attenuation for modelling of the KVue Couchtop for 6X and 10X FFF SRS/SBRT treatmentMethods:Treatment planning simulation studies were done using 6X FFF beams to estimate the dosimetric impact of KVue couchtops (including the Q‐Fix IGRT [carbon fiber] and Calypso [nonconductive Kevlar material]) with a structure model obtained from a research workstation (Eclipse, advanced planning interface (API) v13). Prior to installation on the Varian Edge linac, the couchtop along with (Kevlar) rails were CT scanned with the rails at various positions. An additional scan with the couchtop 15cm above the CT table top was obtained with 20cm solid water to facilitate precised/indexed data acquisition. Measurements for attenuation were obtained for field sizes of 2, 4 and 10 cm2 at 42 gantry angles including 6 pairs of opposing fields and other angles for oblique delivery where the beams traversed the couchtop and or rails. The delivery was fully automated with xml scripts running in developer mode. The results were then used to determine an accurate structure model for AAA (Eclipse v11) planning of IMRT and RapidArc delivery.Results:The planning simulation relative dose attenuation for oblique entry was not significantly different than the Exact IGRT or BrainLab iBeam couch except that the rails added 6% additional attenuation. The relative attenuation measurements for PA, PA (rails: inner position), oblique, oblique (rails: outer position), oblique (rails: inner position) were: −2.0%, −2.5%, −15.6%, −2.5%, −5.0% for 6X FFF and −1.4%, −1.5%, −12.2%, − 2.5%, −5.0% for 10X FFF with slight decrease in attenuation versus field size. A Couch structure model (with HU values) was developed. Calculation compared to measurement showed good agreement except for oblique (rails: outer position) where differences approached a magnitude of 6%.Conclusion:A model of the couch structures has been developed accounting for attenuation for FFF beams.
SU‐F‐BRE‐11: Neutron Measurements Around the Varian TrueBeam Linac
Authors: Maglieri R , Liang L , Evans M , Licea A , Dubeau J , Witharana S , DeBlois F , Seuntjens J , Kildea J 
Published: July 2014

Purpose:With the emergence of flattening filter free (FFF) photon beams, several authors have noted many advantages to their use. One such advantage is the decrease in neutron production by photonuclear reactions in the linac head. In the present work we investigate the reduction in neutrons from a Varian TrueBeam linac using the Nested Neutron Spectrometer (NNS, Detec). The neutron spectrum, total fluence and source strength were measured and compared for 10 MV with and without flattening filter and the effect of moderation by the room and maze was studied for the 15 MV beam.Methods:The NNS, similar to traditional Bonner sphere detectors but operated in current mode, was used to measure the neutron fluence and spectrum. The NNS was validated for use in high dose rate environments using Monte Carlo simulations and calibrated at NIST and NRC Canada. Measurements were performed at several positions within the treatment room and maze with the linac jaws closed to maximize neutron production.Results:The measurements showed a total fluence reduction between 35‐40% in the room and maze when the flattening filter was removed. The neutron source strength Qn was calculated from in‐room fluence measurements and was found to be 0.042 × 102 n/Gy, 0.026 × 102 n/Gy and 0.59 × 1012 n/Gy for the 10 MV, the 10 MV FFF and 15 MV beams, respectively. We measured ambient equivalent doses of 11 mSv/hr, 7 mSv/hr and 218 mSv/hr for the 10 MV, 10 MV FFF and 15 MV by the head.Conclusion:Our measurements revealed a decrease in total fluence, neutron source strength and equivalent dose of approximately 35‐40% across the treatment room for the FFF compared to FF modes. This demonstrates, as expected, that the flattening filter is a major component of the neutron production for the TrueBeam.The authors greatly acknowledge support form the Canadian Nuclear Commission and the Natural Sciences and Engineering Research Council of Canada through the CREATE program. Co‐authors Dubeau and Witharana are employees of Detec (Gatineau, Quebec), manufacturer of the Nested Neutron Spectrometer.
SU‐F‐BRE‐12: Optical Resonator Water Calorimeter
Authors: Abraham J , DeMarco J , Low D 
Published: July 2014

Purpose:Water calorimetry based on resistance thermometry has matured as a primary standard. Developing an optical technique hold the promise to push the boundaries of what is currently achievable with dosimetry. We will present a feasibility study and the current progress of construction of a Fabry‐Perot resonator for dose to water measurement. Additionally, estimations of the theoretical limits resonator sensitivity and potential sources of noise for the system are described.Methods:A temperature change from the dose to water would be measured by the change in the index of refraction from the water in the cavity. Calculations are presented of the expected signal from the resonator for dose to water. The Fabry‐Perot resonator constructed from optical quality narrowband mirrors is described. A water cell will be inserted into the cavity gap to provide the medium swept cavity length technique is explored as a specific implementation of this technique.Results:Calculations indicate that a dose to water on the order of a Gray is measureable with a reasonably implementable system. A resonator is currently under construction and progress towards a proof of principle measurement will be presented. The primary sources of noise, in order of importance, are expected to be; optical absorption by the medium, mechanical perturbations of the cavity length and thermal expansion of the optical mounts. Estimations of these noise sources and mitigation techniques will be discussed.Conclusion:A Fabry‐Perot resonator is a promising technique for measuring the absorbed dose to water from a radiotherapy beam. This technique has the potential to serve as a check on the current primary standard for dose to water measurements. As well, i0074 may be the foundation for a new class of optical property based dosimetry measurement.
SU‐F‐BRE‐13: Replacing Pre‐Treatment Phantom QA with 3D In‐Vivo Portal Dosimetry for IMRT Breast Cancer
Authors: Stroom J , Vieira S , Olaciregui‐Ruiz I , Rozendaal R , van Herk M , Moser E , Greco C 
Published: July 2014

Purpose:Pre‐treatment QA of individual treatment plans requires costly linac time and physics effort. Starting with IMRT breast treatments, we aim to replace pre‐treatment QA with in‐vivo portal dosimetry.Methods:Our IMRT breast cancer plans are routinely measured using the ArcCheck device (SunNuclear). 2D‐Gamma analysis is performed with 3%/3mm criteria and the percentage of points with gamma<1 (nG1) is calculated within the 50% isodose surface. Following AAPM recommendations, plans with nG1<90% are approved; others need further inspection and might be rejected. For this study, we used invivo portal dosimetry (IPD) to measure the 3D back‐projected dose of the first three fractions for IMRT breast plans. Patient setup was online corrected before for all measured fractions. To reduce patient related uncertainties, the three IPD results were averaged and 3D‐gamma analysis was applied with abovementioned criteria . For a subset of patients, phantom portal dosimetry (PPD) was also performed on a slab phantom.Results:Forty consecutive breast patients with plans that fitted the EPID were analysed. The average difference between planned and IPD dose in the reference point was −0.7+/−1.6% (1SD). Variation in nG1 between the 3 invivo fractions was about 6% (1SD). The average nG1 for IPD was 89+/−6%, worse than ArcCheck (95+/−3%). This can be explained by patient related factors such as changes in anatomy and/or model deficiencies due to e.g. inhomogeneities. For the 20 cases with PPD, mean nG1 was equal to ArcCheck values, which indicates that the two systems are equally accurate. These data therefore suggest that proper criteria for 3D invivo verification of breast treatments should be nG1>80% instead of nG1>90%, which, for our breast cases, would result in 5% (2/40) further inspections.Conclusion:First‐fraction in‐vivo portal dosimetry using new gamma‐evaluation criteria will replace phantom measurements in our institution, saving resources and yielding 3D dosimetry of the actual patient treatment.
SU‐F‐BRE‐14: Uncertainty Analysis for Dose Measurements Using OSLD NanoDots
Authors: Kry S , Alvarez P , Stingo F , Followill D 
Published: July 2014

Purpose:Optically stimulated luminescent dosimeters (OSLD) are an increasingly popular dosimeter for research and clinical applications. It is also used by the Radiological Physics Center for remote auditing of machine output. In this work we robustly calculated the reproducibility and uncertainty of the OSLD nanoDot.Methods:For the RPC dose calculation, raw readings are corrected for depletion, element sensitivity, fading, linearity, and energy. System calibration is determined for the experimental OSLD irradiated at different institutions by using OSLD irradiated by the RPC under reference conditions (i.e., standards): 1 Gy in a Cobalt beam. The intra‐dot and inter‐dot reproducibilities (coefficient of variation) were determined from the history of RPC readings of these standards. The standard deviation of the corrected OSLD signal was then calculated analytically using a recursive formalism that did not rely on the normality assumption of the underlying uncertainties, or on any type of mathematical approximation. This analytical uncertainty was compared to that empirically estimated from >45,000 RPC beam audits.Results:The intra‐dot variability was found to be 0.59%, with only a small variation between readers. Inter‐dot variability was found to be 0.85%. The uncertainty in each of the individual correction factors was empirically determined. When the raw counts from each OSLD were adjusted for the appropriate correction factors, the analytically determined coefficient of variation was 1.8% over a range of institutional irradiation conditions that are seen at the RPC. This is reasonably consistent with the empirical observations of the RPC, where the coefficient of variation of the measured beam outputs is 1.6% (photons) and 1.9% (electrons).Conclusion:OSLD nanoDots provide sufficiently good precision for a wide range of applications, including the RPC remote monitoring program for megavoltage beams.This work was supported by PHS grant CA10953 awarded by the NIH (DHHS).
SU‐F‐BRE‐15: Verification of Energy Dependence of MAGAT Polymer Gel at Orthovoltage Energies
Authors: Roed Y , Tailor R , Pinsky L , Ibbott G 
Published: July 2014

Purpose:Investigation of dose response curves of methacrylic acid‐based “MAGAT” gel at different effective energies to verify an energy dependence of polymer‐gel dosimeters for orthovoltage energy x‐rays.Methods:Six small cylindrical MAGAT gel phantoms were exposed to different dose levels; one phantom was unirradiated for background subtraction. This experiment was repeated for three different effective beam energies.24 h post irradiation the spin‐spin relaxation times (T2) were measured with a 4.7 T Bruker MR scanner at 2 cm depth inside the gel. The T2 values were converted to relaxation rates (R2) and plotted against the respective dose levels corresponding to the different effective energies. The resulting dose response curves were compared for a 250 kVp beam, the 250 kVp beam filtered by 6 cm of water, and a 125 kVp beam.Results:The passage of the 250 kVp beam through water resulted in a half‐value‐layer (HVL) change from 1.05 mm Cu to 1.32 mm Cu at 6 cm depth with a change in effective energy from 81.3 keV to 89.5 keV, respectively. The dose response curves showed a shift to higher relaxation rates for the harder beam. The dose response measurements for the 125 kVp beam (HVL: 3.13 mm Al, effective energy: 33.9 keV) demonstrated even higher relaxation rates than for either of the other beams.Conclusion:The MAGAT dose response curves for three different effective energies demonstrate a complex energy dependence, with an apparent decrease in sensitivity at 89.5 keV effective energy. This energy dependence is consistent with observed discrepancies of depth dose data compared with ion‐chamber data. For future investigations of larger volumes, an energy‐dependent sensitivity function is needed to properly assess 3‐dimensional dose distributions.
SU‐F‐BRE‐16: VMAT Commissioning and Quality Assurance (QA) of An Elekta Synergy‐STM Linac Using ICOM Test HarnessTM
Authors: Nguyen A , Rajaguru P , Kaurin D , Paul T , He R , Plowman A , Yang C 
Published: July 2014

Purpose:To establish a set of tests based on the iCOM software that can be used to commission and perform periodic QA of VMAT delivery on the Elekta Synergy‐S, commonly known as the Beam Modulator (BM).Methods:iCOM is used to create and deliver customized treatment fields to characterize the system in terms of 1) MLC positioning accuracy under static and dynamic delivery with full gantry rotation, 2) MLC positioning with known errors, 3) Maximum dose rate, 4) Maximum MLC speed, 5) Maximum gantry speed, 6) Synchronization: gantry speed versus dose rate, and 7) Synchronization: MLC speed versus dose rate. The resulting images were captured on the iView GT and exported in DICOM format to Dosimetry Check™ system for visual and quantitative analysis. For the initial commissioning phase, the system tests described should be supplemented with extensive patient QAs covering all clinically relevant treatment sites.Results:The system performance test suite showed that on our Synergy‐S, MLC positioning was accurate under both static and dynamic deliveries. Intentional errors of 1 mm were also easily identified on both static & dynamic picket fence tests. Maximum dose rate was verified with stop watch to be consistently between 475‐480 MU/min. Maximum gantry speed and MLC speed were 5.5 degree/s and 2.5 cm/s respectively. After accounting for beam flatness, both synchronization tests, gantry versus dose rate and MLC speed versus dose rate, were successful as the fields were uniform across the strips and there were no obvious cold/hot spots.Conclusion:VMAT commissioning and quality assurance should include machine characterization tests in addition to patient QAs. Elekta iCOM is a valuable tool for the design of customized VMAT field with specific MU, MLC leaf positions, dose rate, and indirect control of MLC and gantry speed at each of its control points.
SU‐F‐BRD‐01: A Logistic Regression Model to Predict Objective Function Weights in Prostate Cancer IMRT
Authors: Boutilier J , Chan T , Craig T , Lee T , Sharpe M 
Published: July 2014

Purpose:To develop a statistical model that predicts optimization objective function weights from patient geometry for intensity‐modulation radiotherapy (IMRT) of prostate cancer.Methods:A previously developed inverse optimization method (IOM) is applied retrospectively to determine optimal weights for 51 treated patients. We use an overlap volume ratio (OVR) of bladder and rectum for different PTV expansions in order to quantify patient geometry in explanatory variables. Using the optimal weights as ground truth, we develop and train a logistic regression (LR) model to predict the rectum weight and thus the bladder weight. Post hoc, we fix the weights of the left femoral head, right femoral head, and an artificial structure that encourages conformity to the population average while normalizing the bladder and rectum weights accordingly. The population average of objective function weights is used for comparison.Results:The OVR at 0.7cm was found to be the most predictive of the rectum weights. The LR model performance is statistically significant when compared to the population average over a range of clinical metrics including bladder/rectum V53Gy, bladder/rectum V70Gy, and mean voxel dose to the bladder, rectum, CTV, and PTV. On average, the LR model predicted bladder and rectum weights that are both 63% closer to the optimal weights compared to the population average. The treatment plans resulting from the LR weights have, on average, a rectum V70Gy that is 35% closer to the clinical plan and a bladder V70Gy that is 43% closer. Similar results are seen for bladder V54Gy and rectum V54Gy.Conclusion:Statistical modelling from patient anatomy can be used to determine objective function weights in IMRT for prostate cancer. Our method allows the treatment planners to begin the personalization process from an informed starting point, which may lead to more consistent clinical plans and reduce overall planning time.
SU‐F‐BRD‐02: Application of ARCHERRT‐‐ A GPU‐Based Monte Carlo Dose Engine for Radiation Therapy ‐‐ to Tomotherapy and Patient‐Independent IMRT
Authors: Su L , Yang Y , Bednarz B , Sterpin E , Du X , Liu T , Xu X 
Published: July 2014

Purpose:As a module of ARCHER ‐‐ Accelerated Radiation‐transport Computations in Heterogeneous EnviRonments, ARCHERRT is designed for RadioTherapy (RT) dose calculation. This paper describes the application of ARCHERRT on patient‐dependent TomoTherapy and patient‐independent IMRT. It also conducts a “fair” comparison of different GPUs and multicore CPU.Methods:The source input used for patient‐dependent TomoTherapy is phase space file (PSF) generated from optimized plan. For patient‐independent IMRT, the open filed PSF is used for different cases. The intensity modulation is simulated by fluence map. The GEANT4 code is used as benchmark. DVH and gamma index test are employed to evaluate the accuracy of ARCHERRT code. Some previous studies reported misleading speedups by comparing GPU code with serial CPU code. To perform a fairer comparison, we write multi‐thread code with OpenMP to fully exploit computing potential of CPU. The hardware involved in this study are a 6‐core Intel E5‐2620 CPU and 6 NVIDIA M2090 GPUs, a K20 GPU and a K40 GPU.Results:Dosimetric results from ARCHERRT and GEANT4 show good agreement. The 2%/2mm gamma test pass rates for different clinical cases are 97.2% to 99.7%. A single M2090 GPU needs 50~79 seconds for the simulation to achieve a statistical error of 1% in the PTV. The K40 card is about 1.7∼1.8 times faster than M2090 card. Using 6 M2090 card, the simulation can be finished in about 10 seconds. For comparison, Intel E5‐2620 needs 507∼879 seconds for the same simulation.Conclusion:We successfully applied ARCHERRT to Tomotherapy and patient‐independent IMRT, and conducted a fair comparison between GPU and CPU performance. The ARCHERRT code is both accurate and efficient and may be used towards clinical applications.
SU‐F‐BRD‐03: Determination of Plan Robustness for Systematic Setup Errors Using Trilinear Interpolation
Authors: Fix MK , Volken W , Frei D , Terribilini D , Dal Pra A , Schmuecking M , Manser P 
Published: July 2014

Purpose:Treatment plan evaluations in radiotherapy are currently ignoring the dosimetric impact of setup uncertainties. The determination of the robustness for systematic errors is rather computational intensive. This work investigates interpolation schemes to quantify the robustness of treatment plans for systematic errors in terms of efficiency and accuracy.Methods:The impact of systematic errors on dose distributions for patient treatment plans is determined by using the Swiss Monte Carlo Plan (SMCP). Errors in all translational directions are considered, ranging from −3 to +3 mm in mm steps. For each systematic error a full MC dose calculation is performed leading to 343 dose calculations, used as benchmarks. The interpolation uses only a subset of the 343 calculations, namely 9, 15 or 27, and determines all dose distributions by trilinear interpolation. This procedure is applied for a prostate and a head and neck case using Volumetric Modulated Arc Therapy with 2 arcs. The relative differences of the dose volume histograms (DVHs) of the target and the organs at risks are compared. Finally, the interpolation schemes are used to compare robustness of 4‐ versus 2‐arcs in the head and neck treatment plan.Results:Relative local differences of the DVHs increase for decreasing number of dose calculations used in the interpolation. The mean deviations are <1%, 3.5% and 6.5% for a subset of 27, 15 and 9 used dose calculations, respectively. Thereby the dose computation times are reduced by factors of 13, 25 and 43, respectively. The comparison of the 4‐ versus 2‐arcs plan shows a decrease in robustness; however, this is outweighed by the dosimetric improvements.Conclusion:The results of this study suggest that the use of trilinear interpolation to determine the robustness of treatment plans can remarkably reduce the number of dose calculations. This work was supported by Varian Medical Systems.This work was supported by Varian Medical Systems
SU‐F‐BRD‐04: Development of a Secondary MU Calculation Tool for An Integrated MR‐LINAC
Authors: Chen G , Li X 
Published: July 2014

Purpose:To develop a fast secondary MU calculation tool for an integrated MR‐Linac, an emerging technology for delivering image‐guided on‐line adaptive therapy.Methods:A software tool was developed to implement a modified Clarkson integration algorithm for point‐dose calculation, considering the dosimtric effect of a magnetic field. A research planning system, considering the presence of a perpendicular 1.5 T magnetic field, was used to extract the beam data (e.g., depth doses and beam profiles) required for the MU calculation in homogeneous phantom of 60×60×40 cm3 for a prototype of MR‐Linac integrating a 1.5 T MR scanner with 6MV photon beams. These dosimetric data may be replaced with those to be collected during the commissioning measurement of the MR‐Linac.Results:The presence of the magnetic field resulted in noticeable changes including (1) shifts in beam profiles for small fields (< 2×2 cm2), and (2) changes in central‐axis doses when one of field edges is < 2 cm away from the central axis. For example, the maximum change in central‐axis dose was up to 8% for one of the field borders with a distance away from the central axis of <1 cm. These changes are relevant for the MU calculation particularly for IMRT and VMAT, where most of segments are small. These magnetic field affected beam profiles and depth doses were included in the software tool. The MU calculations from the software tool for selective representative plans were found to agree with those from the research planning system within 10%.Conclusion:The presence of a perpendicular magnetic field results in noticeable changes in beam profiles and depth doses for small fields. These changes are included in the secondary MU calc33u3lation to be used as a redundancy check for an integrated MR‐Linac.