bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐460: Impact of the LINAC Repetition Rate On a High‐Resolution Liquid Ionization Chamber Array for Patient‐Specific QA
Authors: Wang S , Driewer J , Zheng D , Lei Y , Zhang Q , Zhu X , Li S , Enke C , Xu B , Zhou S 
Published: June 2015

Purpose:The purpose of this study is to investigate the LINAC repetition‐rate (dose‐rate) dependence of OCTAVIUS 1000SRS liquid ionization chamber (LIC) array for patient specific QA of SRT plans delivered with flattening‐filter‐free (FFF) beams.Methods:1) The repetition‐rate dependence of 1000SRS was measured in a phantom constructed with 5‐cm solid water above and below the array for build‐up and backscatter. A 0.3cc calibrated ion chamber was also placed along the central axis 2.3cm below the center chamber of the array for normalizing LINAC output fluctuation. The signals from the center chamber of the array under different repetition rates in the range of 400–2400 MU/min for 6xFFF and 10xFFF beams on a Varian TrueBeamSTx LINAC, normalized by the independent chamber readings, were analyzed for the array response dependence on repetition rates. 2) Twelve Step‐and‐shoot IMRS QA plans (6xFFF and 10xFFF) were delivered to the array under different repetition rates for analysis and comparison. 3) The absolute doses measured by the center chamber were compared to measurements using an independent ionization chamber with the identical setup, taken as the gold standard. 4) The correction factors based on the actual delivery repetition rate were applied to the measurements, and the results were compared again to the gold standard.Results:1) The 1000SRS array exhibited repetition‐rate dependence for FFF beams, up to 5% for 6xFFF and 10% for 10xFFF; 2) The array showed clinically‐acceptable repetition‐rate dependence for regular flattened beams; 3) This repetition‐rate dependence significantly affected the measurement accuracy, thereby affecting IMRS QA results; 4) By applying an empirical repetition‐rate correction, the corrected measurements agreed better with the gold standard ion chamber measurements.Conclusion:OCTAVIUS 1000SRS LIC array exhibited considerable repetition‐rate dependence for FFF beams, which will affect the accuracy of the absolute QA measurements, especially for IMRS plans with the step‐and‐shoot technique.
SU‐E‐T‐472: Improvement of IMRT QA Passing Rate by Correcting Angular Dependence of MatriXX
Authors: Chen Q , Watkins W , Kim T , Neal B 
Published: June 2015

Purpose:Multi‐channel planar detector arrays utilized for IMRT‐QA, such as the MatriXX, exhibit an incident‐beam angular dependent response which can Result in false‐positive gamma‐based QA results, especially for helical tomotherapy plans which encompass the full range of beam angles. Although MatriXX can use with gantry angle sensor to provide automatically angular correction, this sensor does not work with tomotherapy. The purpose of the study is to reduce IMRT‐QA false‐positives by correcting for the MatriXX angular dependence.Methods:MatriXX angular dependence was characterized by comparing multiple fixed‐angle irradiation measurements with corresponding TPS computed doses. For 81 Tomo‐helical IMRT‐QA measurements, two different correction schemes were tested: (1) A Monte‐Carlo dose engine was used to compute MatriXX signal based on the angular‐response curve. The computed signal was then compared with measurement. (2) Uncorrected computed signal was compared with measurements uniformly scaled to account for the average angular dependence. Three scaling factor (+2%, +2.5%, +3%) were tested.Results:The MatriXX response is 8% less than predicted for a PA beam even when the couch is fully accounted for. Without angular correction, only 67% of the cases pass the >90% points γ<1 (3%, 3mm). After full angular correction, 96% of the cases pass the criteria. Of three scaling factors, +2% gave the highest passing rate (89%), which is still less than the full angular correction method. With a stricter γ(2%,3mm) criteria, the full angular correction method was still able to achieve the 90% passing rate while the scaling method only gives 53% passing rate.Conclusion:Correction for the MatriXX angular dependence reduced the false‐positives rate of our IMRT‐QA process. It is necessary to correct for the angular dependence to achieve the IMRT passing criteria specified in TG129.
SU‐E‐T‐474: Improvements to Intra‐Oral Shield Design for Electron Beam Treatments: Use of Multi‐Layered Metal Foils
Authors: Butson M 
Published: June 2015

Purpose:Intraoral electron shields used in radiotherapy are designed to minimize radiation exposure to non‐treatment tissue. Sites where shields are used include but are not limited to, the treatment of lips, cheeks and ears whilst shielding the underlying oral cavity, tongue, gingival or temporal region. However their use produces an enhancement in dose on the beam side caused by an increase in electron backscatter radiation. This work designs a new shield incorporating copper, aluminium and wax in a step down filter arrangement to minimise backscatter whilst minimizing overall shield thickness.Methods:For electron beams ranging from 6 MeV to 10 MeV, shields of varying designs and thicknesses were assessed to determine the thinnest shield design that could be produced whilst minimising backscattered radiation to a clinically acceptable level. This was performed with conventional lead and wax shields as well as varying quantities of aluminium and copper foils.Results:From tested shield designs, a new shield design of 4 mm lead, 0.6 mm copper, 1.0 mm aluminium and 1.5 mm wax (3.1 mm added filtration, 7.1 mm total thickness) provided a clinically acceptable (no greater than 110% dose) backscatter and transmission reduction and matched a standard 4.5 mm lead and 10 mm wax (total thickness 14.5 mm) electron shield. Dose enhancement values of no more than 10 % were measured utilising this shield design with a 50 % reduction in shield thickness.Conclusion:The thinner layered shield reduced backscattered radiation dose to less than 10% enhancement for beam energies on 10 MeV and less and will allow easier patient set up. The thinner shields are tolerated better by patients when mucosal reactions occur as they place less physical pressure on these sites during treatment due to their smaller size and thickness.
SU‐E‐T‐475: Improvements to Total Body Irradiation Dosimetry Efficiency with EBT3 Radiochromic Film and a Template System
Authors: Butson M , Pope D , Whitaker M 
Published: June 2015

Purpose:Total Body Irradiation (TBI) treatments are mainly used in a preparative regimen for haematopoietic stem cell (or bone marrow) transplantation. Our standard regimen is a 12 Gy / 6 fraction bi‐daily technique. To evaluate the delivered dose homogeneity to the patient, EBT3 Gafchromic film is positioned at the head, neck, chest, pelvis and groin for all fractions. A system has been developed to simply and accurately prepare and readout the films for patient dose assessment.Methods:A process involving easy preparation and analysis has been produced to minimise the time requirements for TBI dosimetry. One sheet of EBT3 film is used to prepare treatment dosimeters for all fractions, including calibration films, and an automated dose analysis system for easy evaluation and calculation of estimated in‐vivo doses was developed. A desktop scanner is used with a dedicated TBI film template to accurately position the films for Image J analysis and extraction. Dental wax bolus and zip‐lock bag holders are used to hold the EBT3 film in place during irradiation.Results:To adequately provide dosimetry information for a 6 fraction, TBI patient, only one sheet of Gafchromic EBT3 film is required. The dosimeters are cut, using a template, into 19 mm squares which are then placed between two 30 mm × 30 mm × 4.5 mm wax blocks for bolus. All packages are prepared before the first treatment fraction. The scanning and analysis process can be completed in less than 10 minutes after a 240 min development period. Results have shown that a high level of accuracy and reproducibility can be achieved using the template system provided.Conclusion:Gafchromic EBT3 film provides an adequate in‐vivo dosimetry measure for TBI patients. Using a template based system on a dedicated desktop scanner, in‐vivo results can be ascertained quickly and accurately.
SU‐E‐T‐480: IMRT/VMAT QA Employing a High Resolution Measurement Array: Initial Experience and Limitations
Authors: Gainey M , Saum R , Rothe T , Knobe S , Luebke J , Kuechler S , Wiehle R , Kollefrath M , Bruggmoser G 
Published: June 2015

Purpose:Patient specific QA for IMRT/VMAT is time‐consuming. A high resolution ionization chamber array was employed which rotates synchronously with the gantry. Commissioning, initial experience and limitations of this measurement technique will be discussed.Methods:A high resolution ionization chamber array, Octavius1500 (PTW‐Freiburg, Germany), was employed with the Octavius4D rotating cylindrical phantom. Measured plans are reconstructed into a 3D dose distribution using measured depth dose curves (Verisoft 6.0 PTW‐Freiburg). Plans of varying complexity were selected from our patient collective treated at a TrueBeam 1.5 linac (Varian Medical Systems) with HD120 MLC (VMS). Cross‐calibration was performed using a thimble chamber (30016, PTW‐Freiburg) placed within the cylindrical phantom (SSD 840mm, SCD 1000mm). All dose distributions were recalculated using a 1.5mm dose grid (Eclipse, AAA10.0.28/Acuros10.0.28, VMS) using a virtual homogeneous cylindrical phantom provided by the array manufacturer (density 1.016 gcm‐3). All analyses were performed using Verisoft and compared to routine QA analysis (Octavius729 with octagonal phantom) results.Results:Depth dose curves from 1cm × 1cm to 26cm × 26cm were measured for 3D dose calculation commissioning in Verisoft 6.0. Excellent agreement was observed between TPS PDD and PDD derived from the Octavius1500 array measurement. For highly modulated plans the overall 3D gamma (2.0mm, 3.0%) ranged between 91.3% to 96.9%. The Octavius729 (2D) array results ranged from 97.9 to 100.0% for PTVs.Conclusion:The Octavius1500 and 4D cylindrical phantom provides an integrated QA solution. Complex VMAT plans, comprising multiple PTVs, can be verified with a single (rotating) measurement of all arcs. Hitherto two measurements (horizontal and vertical) had to be performed per PTV. Overall the results are good. However, some refinement may need to be made to the reconstruction. Further work needs to be done to determine appropriate action levels for routine analysis.
SU‐E‐T‐481: In Vivo and Post Mortem Animal Irradiation: Measured Vs. Calculated Doses
Authors: Heintz P , Heintz B , Sandoval D , Weber W , Melo D , Guilmette R 
Published: June 2015

Purpose:Computerized radiation therapy treatment planning is performed on almost all patients today. However it is seldom used for laboratory irradiations. The first objective is to assess whether modern radiation therapy treatment planning (RTP) systems accurately predict the subject dose by comparing in vivo and decedent dose measurements to calculated doses. The other objective is determine the importance of using a RTP system for laboratory irradiations.Methods:5 MOSFET radiation dosimeters were placed enterically in each subject (2 sedated Rhesus Macaques) to measure the absorbed dose at 5 levels (carina, lung, heart, liver and rectum) during whole body irradiation. The subjects were treated with large opposed lateral fields and extended distances to cover the entire subject using a Varian 600C linac. CT simulation was performed ante‐mortem (AM) and post‐mortem (PM). To compare AM and PM doses, calculation points were placed at the location of each dosimeter in the treatment plan. The measured results were compared to the results using Varian Eclipse and Prowess Panther RTP systems.Results:The Varian and Prowess treatment planning system agreed to within in +1.5% for both subjects. However there were significant differences between the measured and calculated doses. For both animals the calculated central axis dose was higher than prescribed by 3–5%. This was caused in part by inaccurate measurement of animal thickness at the time of irradiation. For one subject the doses ranged from 4% to 7% high and the other subject the doses ranged 7% to 14% high when compared to the RTP doses.Conclusions:Our results suggest that using proper CT RTP system can more accurately deliver the prescribed dose to laboratory subjects. It also shows that there is significant dose variation in such subjects when inhomogeneities are not considered in the planning process.
SU‐E‐T‐482: In Vivo Dosimetry of An Anthropomorphic Phantom by Using the RADPOS System for Proton Beam Therapy
Authors: Kohno R , Yamaguchi H , Motegi K , Hotta K , Nishioka S , Dohmae T , Akimoto T 
Published: June 2015

Purpose:Delivered doses in an anthropomorphic phantom were evaluated by using the RADPOS system for proton beam therapy.Methods:The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFET dosimetry, allowing simultaneous online measurements of dose and spatial position. Through the RADPOS system, dose evaluation points can be determined. In vivo proton dosimetry was evaluated by using the RADPOS system and anthropomorphic head and neck phantom. MOSFET doses measured at 3D positions obtained with the RADPOS were compared to the treatment plan values that were calculated by a simplified Monte Carlo (SMC) method. Although the MOSFET response depends strongly on the linear energy transfer (LET) of proton beam, the MOSFET responses to proton beams were corrected with the SMC. Here, the SMC calculated only dose deposition determined by the experimental depth–dose distribution and lateral displacement of protons due to both multiple scattering effect in materials and incident angle. As a Result, the SMC could quickly calculate accurate doses in even heterogeneities.Results:In vivo dosimetry by using the RADPOS, as well as the MOSFET doses agreed in comparison with calculations by the SMC in the range of −3.0% to 8.3%. Most measurement errors occurred because of the uncertainties of dose calculations due to the position error of 1 mm.Conclusion:We evaluated the delivered doses in the anthropomorphic phantom by using the RADPOS system for proton beam therapy. The MOSFET doses agreed in comparison with calculations by the SMC within the measurement error. Therefore, we could successfully control the uncertainties of the measurement positions by using the RADPOS system within 1 mm in in vivo proton dosimetry. We aim for the clinical application of in vivo proton dosimetry with this RADPOS system.
SU‐E‐T‐485: In Vivo Dosimetry with EBT3 Radiochromic Films for TBI Treatments
Authors: Lozares S , Gracia M , Olasolo J , Gallardo N , Fuentemilla N , Pellejero S , Miquelez S , Maneru F , Martin M , Bragado L , Rubio A 
Published: June 2015

Purpose:Total body irradiation (TBI) is a technique that requires special equipment to control “in vivo” the dose to the patient because it is a complex technique performed in extraordinary conditions. There are several devices to perform this task (diodes, TLDs, ionization chambers, MOSFET). In this paper we study the possibility of performing these measurements with radiochromic films EBT3 properly calibrated. This method has been compared to the PTW diodes system for TBI.Methods:Once made the TC to the patients, we measured different thicknesses of the relevant areas of the body (head, neck, chest with or without arms, umbilicus area, knees and ankles); for each of these thicknesses we measured dose rate (cGy / UM) in RW3 phantom, in TBI conditions, with ionization chamber in the center; in turn, the input diode and the output of each configuration is placed to assign dose to each set of diodes. Movie calibration is performed according to manufacturer's recommendations but TBI conditions. The dose at the center of each thickness compared to a linear interpolation of the dose at the entrance and exit, resulting in an adequate approximation. Finally in each session for each patient put a piece of film (2×2 cm2) at the entrance and another at the exit in each area, obtaining these readings and interpolating the estimated center dose, as with the diodes.Results:These results show a greater homogeneity in the distribution for use with film and validate the use of the same for this task and, if necessary, to avoid purchasing diode group if they have not.Conclusion:By using radiochromic films for this technique gives us a proper calculation of the dose received by the patient in the absence of other methods, or gives us a second additional track that already used normally.
SU‐E‐T‐493: Influence of Filtered and Flatting Filter Free Photon Beam of 10 Megavolts Energy On Rapid Arc Radiotherapy Planning for Cervix Carcinoma
Authors: Girigesh Y , Kumar L , Raman K , Mishra M 
Published: June 2015

Purpose:Aim of this study is to determine the dosimetric influence of Filtered and Flatting Filter Free Photon Beam of 10 MV energy on RA planning for Ca. Cervix.Methods:CT data sets of eleven patients reported with carcinoma cervix were used for RA planning for 10MV _FFB and 10MV_FFFB. RA plans were generated using two full arcs.All RA plans were generated to deliver a dose of 50.4Gy in 28 fractions for PTV and ALARA for OAR's. All plans were analysed for PTV Coverage, conformity Index, homogeneity index, dose to OAR's, integral dose to normal tissue and total monitor units were studied.Results:DVH was used to evaluate RA plans for both 10MV_FFB and 10MV_FFFB photon beam. Planning results show a comparable PTV coverage for both energies. Results shows volume of PTV receiving prescription dose were 95.10+ 0.09% and 95.09 +0.11%, and volume of PTV receiving a dose of 107% is 0.45+0.96% and 5.25+8.9%, homogeneity index (HI) were 1.051+0.007 and 1.066+0.008, Conformity Index(CI) were 1.003+0.019 and 1.012+0.013, Mean Integral dose were 2.65+0.34 and 2.60+0.33(*10−5Gy.cm3) for 10MV_FFB and 10MV_FFFB respectively. 10MV_FB shows statistically significant (p<0.05) improvement in mean doses to bladder, rectum, bowel and mean total number of MU's and also shows remarkable decrease in mean total no. of MU's by 43.7% in comparison to 10MV_FFFB. There is statistically significant (p<0.05) difference found in CI and HI for 10MV_FB in comparison to 10MV _FFF beam. 10MV_FFFB shows statistically significant (p<0.05) for mean NTID and delivers 1.65 % less NTID in comparison to 10 MV_ FB.Conclusion:10MV_FB is superior to 10MV_FFFB for rapid arc planning in case of Cervix carcinomas, it offers better target coverage and OAR's sparing, comparable mean Integral dose to normal tissues and 10 MV_ FB also produced highly conformal and homogeneous dose distribution in comparison to 10MV_FFFB.
SU‐E‐T‐499: Initial Developments of An OpenCL‐Based Cross‐Platform Monte Carlo Dose Engine for Carbon Ion Therapy
Authors: Qin N , Pinto M , Tian Z , Dedes G , Pompos A , Jiang S , Parodi K , Jia X 
Published: June 2015

PurposeDose calculation is of critical importance for carbon ion therapy. Monte Carlo (MC) simulation is considered to be the most accurate method for calculation of absorbed dose and of all the more fundamental physical quantities related to biological effects. The long computation time, however, limits its routine clinical applications. We have recently started developing a fast MC package, gCMC for carbon therapy on a parallel processing platform, e.g. GPU, aiming at achieving sufficient efficiency to enable MC in clinically important tasks. This abstract reports our progress.MethodsgCMC was developed in OpenCL environment. Our initial developments focused on water material. gCMC supported carbon ion transport in the energy range of 1–450 MeV/u. A Class II condensed history algorithm was implemented for charged particle transport simulations with stopping power computed via Bethe‐Bloch equation. Energy straggling and multiple scattering were modeled. Total cross section of nuclear interaction was extracted from Geant4. At present, nuclear interaction events were sampled but transports of secondary particles were not included.ResultsWe tested cases with a homogeneous water phantom and a pencil carbon ion beam with energy of 200–400 MeV/u. When only electro‐magnetic channel was included, dose/fluence difference between gCMC and Geant4 results averaged within 10% isodose line was <0.5% of the maximum dose/fluence. After enabling nuclear interactions without transporting secondary particles, dose and fluence agreed with the corresponding results computed by Geant4 with <1% difference. Due to the support for multiple platforms of OpenCL, gCMC was executable on NVidia and AMD GPUs, and Intel CPUs. It took ∼50 sec to transport 107 200MeV/u source carbon ions on an NVidia Titan GPU card.ConclusionPreliminary studies have demonstrated the accuracy and efficiency of gCMC. With further developments in near future, gCMC will potentially achieve clinically acceptable fast and accurate MC simulations for carbon ion therapy.
SU‐E‐T‐509: Inter‐Observer and Inter‐Modality Contouring Analysis for Organs at Risk for HDR Gynecological Brachytherapy
Authors: Sadeghi P , Banerjee R , Alghamdi M , Phan T , Taggar A , Smith W 
Published: June 2015

PurposeThis study quantifies errors associated with MR‐guided High Dose Rate (HDR) gynecological brachytherapy. Uncertainties in this treatment results from contouring, organ motion between imaging and treatment delivery, dose calculation, and dose delivery. We focus on interobserver and inter‐modality variability in contouring and the motion of organs at risk (OARs) in the time span between the MR and CT scans (∼1 hour). We report the change in organ volume and position of center of mass (CM) between the two imaging modalities.MethodsA total of 8 patients treated with MR‐guided HDR brachytherapy were included in this study. Two observers contoured the bladder and rectum on both MR and CT scans. The change in OAR volume and CM position between the MR and CT imaging sessions on both image sets were calculated.ResultsThe absolute mean bladder volume change between the two imaging modalities is 67.1cc. The absolute mean inter‐observer difference in bladder volume is much lower at 15.5cc (MR) and 11.0cc (CT). This higher inter‐modality volume difference suggests a real change in the bladder filling between the two imaging sessions. Change in Rectum volume inter‐observer standard error of means (SEM) is 3.18cc (MR) and 3.09cc (CT), while the inter‐modality SEM is 3.65cc (observer 1), and 2.75cc (observer 2). The SEM for rectum CM position in the superior‐inferior direction was approximately three times higher than in other directions for both the inter—observer (0.77 cm, 0.92 cm for observers 1 and 2, respectively) and inter‐modality (0.91 cm, 0.95 cm for MR and CT, respectively) variability.ConclusionBladder contours display good consistency between different observers on both CT and MR images. For rectum contouring the highest inconsistency stems from the observers’ choice of the superior‐inferior borders. A complete analysis of a larger patient cohort will enable us to separate the true organ motion from the inter‐observer variability.