bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐83: A Study On Evaluating the Directional Dependency of 2D Seven 29 Ion Chamber Array Clinically with Different IMRT Plans
Authors: Kumar Syam , C.P Aswathi 
Published: June 2015

Purpose:To evaluate the directional dependency of 2D seven 29 ion chamber array clinically with different IMRT plans.Methods:25 patients already treated with IMRT plans were selected for the study. Verification plans were created for each treatment plan in eclipse 10 treatment planning system using the AAA algorithm with the 2D array and the Octavius CT phantom. Verification plans were done 2 times for a single patient. First plan with real IMRT (plan‐related approach) and second plan with zero degree gantry angle (field‐related approach). Measurements were performed on a Varian Clinac‐iX, linear accelerator equipped with a millennium 120 multileaf collimator. Fluence was measured for all the delivered plans and analyzed using the verisoft software. Comparison was done by selecting the fluence delivered in static gantry (zero degree gantry) versus IMRT with real gantry angles.Results:The gamma pass percentage is greater than 97 % for all IMRT delivered with zero gantry angle and between 95%–98% for real gantry angles. Dose difference between the TPS calculated and measured for IMRT delivered with zero gantry angle was found to be between (0.03 to 0.06Gy) and with real gantry angles between (0.02 to 0.05Gy). There is a significant difference between the gamma analysis between the zero degree and true angle with a significance of 0.002. Standard deviation of gamma pass percentage between the IMRT plans with zero gantry angle was 0.68 and for IMRT with true gantry angle was found to be 0.74.Conclusion:The gamma analysis for IMRT with zero degree gantry angles shows higher pass percentage than IMRT delivered with true gantry angles. Verification plans delivered with true gantry angles lower the verification accuracy when 2D array is used for measurement.
SU‐E‐T‐85: A Systematic Analysis of Mono‐Isocentric Techniques for the Treatment of Multiple Metastasis
Authors: Papanikolaou N , Narayanasamy G , Stathakis S , Pappas E , Kirby N , Mavroidis P , Crownover R , Gutierrez A 
Published: June 2015

Purpose:In this planning study, we compared two mono‐isocentric techniques for the treatment of multiple brain metastasis. We hypothesize that, dynamic conformal arc delivery produces significantly more efficient plans of similar quality when compared to volumetric modulated arc therapy (VMAT).Methods:Recently published clinical data demonstrated a benefit in treating multiple brain metastasis (more than four mets) with SRS. A number of publications showed the feasibility of planning such patients with VMAT. In our study, we planned ten SRS patients with three to eight brain metastasis. The Varian eclipse system used four arcs with a VMAT optimized delivery whereas the Brainlab multiple elements software (MME) selected between 3 and 7 optimized arcs to deliver the prescribed dose using a hybrid conformal arc technique (non‐IMRT).Results:We have found that both planning systems achieved the goal to deliver the prescribed dose to the 99.5% of the tumor volume. The tumor doses ranged from 18 to 24Gy, following the RTOG criteria, with most tumors receiving 24Gy. The VMAT and MME plans had varying maximum doses for each tumor and were on average at least 132% of the prescribed dose. We found that once the segmentation and the plan objectives were specified the MME plan was the fastest to compute (less than 3min) whereas the VMAT took on average an hour to calculate with the AAA engine and 15 minutes with the Acuros engine (dose grid resolution of 1mm).Conclusion:Patients with multiple brain metastasis can be treated very efficiently using a mono‐isocentric non‐IMRT delivery technique. Whereas VMAT produces equivalent plans, it takes longer to both compute and deliver with the added complexity of IMRT delivery.UTHSCSA, division of medical physics has a research grant with Brainlab
SU‐E‐T‐90: Accuracy of Calibration of Lithium‐6 and ‐7 Enriched LiF TLDs for Neutron Measurements in High Energy Radiotherapy
Authors: Keehan S , Franich R , Taylor M , Lonski P , Kron T 
Published: June 2015

Purpose:To determine the potential error involved in the interpretation of neutron measurements from medical linear accelerators (linacs) using TLD‐600H and TLD‐700H if standard AmBe and 2⁵2Cf neutron sources are used for calibration without proper inclusion of neutron energy spectrum information.Methods:The Kerma due to neutrons can be calculated from the energy released by various nuclear interactions (elastic and inelastic scatter, (n,α), (n,p), (n,d), (n,t), (n,2n), etc.). The response of each TLD can be considered the sum of the neutron and gamma components; each proportional to the Kerma. Using the difference between the measured TLD responses and the ratio of the calculated Kerma for each material, the neutron component of the response can be calculated. The Monte Carlo code MCNP6 has been used to calculate the neutron energy spectra resulting from photonuclear interactions in a Varian 21EX linac. TLDs have been exposed to the mixed (γ‐n) field produced by a linac and AmBe and 2⁵2Cf standard neutron sources.Results:For dosimetry of neutrons from AmBe or 2⁵2Cf sources, assuming TLD‐700H insensitivity to neutrons will Result in 10% or 20% overestimation of neutron doses respectively.For dosimetry of neutrons produced in a Varian 21EX, applying a calibration factor derived from a standard AmBe or 2⁵2Cf source will Result in an overestimation of neutron fluence, by as much as a factor of 47.The assumption of TLD‐700H insensitivity to neutrons produced by linacs leads to a negligible error due to the extremely high Kerma ratio (600H/700H) of 3000 for the assumed neutron spectrum.Conclusion:Lithium‐enriched TLDs calibrated with AmBe and/or 2⁵2Cf neutron sources are not accurate for use under the neutron energy spectrum produced by a medical linear accelerator.
SU‐E‐T‐98: An Analysis of TG‐51 Electron Beam Calibration Correction Factor Uncertainty
Authors: Lee P , Alvarez P , Taylor P , Lowenstein J , Molineu A , Kry S , Followill D 
Published: June 2015

Purpose:To analyze the uncertainty of the TG‐51 electron beam calibration correction factors for farmer type ion chambers currently used by institutions visited by IROC Houston.Methods:TG‐51 calibration data were collected from 181 institutions visited by IROC Houston physicists for 1174 and 197 distinct electron beams from modern Varian and Elekta accelerators, respectively. Data collected and analyzed included ion chamber make and model, nominal energy, ND,w, I5₀, R5₀, k'R5₀, dref, Pgr and pdd(dref). k'R5₀ data for parallel plate chambers were excluded from the analysis.Results:Unlike photon beams, electron nominal energy is a poor indicator of the actual energy as evidenced by the range of R5₀ values for each electron beam energy (6–22MeV). The large range in R5₀ values resulted k'R5₀ values with a small standard deviation but large range between maximum value used and minimum value (0.001–0.029) used for a specific Varian nominal energy. Varian data showed more variability in k'R5₀ values than the Elekta data (0.001–0.014). Using the observed range of R5₀ values, the maximum spread in k'R5₀ values was determined by IROC Houston and compared to the spread of k'R5₀ values used in the community. For Elekta linacs the spreads were equivalent, but for Varian energies of 6 to 16MeV, the community spread was 2 to 6 times larger. Community Pgr values had a much larger range of values for 6 and 9 MeV values than predicted. The range in Varian pdd(dref ) used by the community for low energies was large, (1.4–4.9 percent), when it should have been very close to unity. Exradin, PTW Roos and PTW farmer chambers ND,w values showed the largest spread, ≥11 percent.Conclusion:While the vast majority of electron beam calibration correction factors used are accurate, there is a surprising spread in some of the values used.
SU‐E‐T‐103: An Evaluation of Multiple Irradiations of the IROC Houston QA Center Anthropomorphic Liver Phantom
Authors: Alvarez P , Molineu A , Lujano C , Nguyen T , Followill D 
Published: June 2015

Purpose:Analyze the results from irradiations of an anthropomorphic liver phantom based on irradiation technique and number of isocenters used for the SBRT delivery.Methods:The phantom consists of a water‐fillable plastic shell that has a polystyrene insert, representing the liver which includes two Solid WaterTM targets (PTV1 and PTV2) mimicking liver metastases. The two targets, PTV1 and PTV2 are non‐coplanar and are an ovoid 2 cm in diameter and 2.5 cm long and a 3 cm diameter sphere, respectively. Each PTV houses one TLD and 2 planes of radiochromic film. The phantom and a motion table to simulate respiratory motion is sent to institutions sthat are instructed to design and deliver a stereotactic treatment plan that delivers 6 Gy to ≥ 95% of each PTV. The maximum motion of the phantom on the motion table was 1 cm in the superior‐inferior direction.Results:Irradiations from 93 institutions have been analyzed. The acceptance criteria are ±7% for the TLD and 85% of the pixels in a region surrounding each PTV passing a ±7%/4 mm global gamma analysis. Sixty‐seven (71%) irradiations meet this criteria. The majority, 74 (80%), of the irradiations were performed with IMRT. 73% of the IMRT deliveries were within criteria and 68% of the 3D CRT delivery were within criteria. 32 of the irradiations had a single isocenter plan, 50 were performed with two isocenters and 11 irradiations were performed with CyberKnife and TomoTherapy units where the concept of isocenter is not applicable. The pass rate for the single, dual and no isocenter irradiations were 69%, 74% and 73%, respectively and are not statistically different.Conclusion:The pass rate for the anthropomorphic liver phantom is approximately 70%. There does not seem to be any correlation with number of isocenters used or irradiation technique used for the delivery.This work was supported by PHS CA180803 awarded by NCI, DHHS
SU‐E‐T‐104: An Examination of Dose in the Buildup and Build‐Down Regions
Authors: Tome W , Kuo H , Phillips J 
Published: June 2015

Purpose:To examine dose in the buildup and build‐down regions and compare measurements made with various models and dosimetersMethods:Dose was examined in a 30×30cm 2 phantom of water‐equivalent plastic with 10cm of backscatter for various field sizes. Examination was performed with radiochromic film and optically‐stimulated‐luminescent‐dosimeter (OSLD) chips, and compared against a plane‐parallel chamber with a correction factor applied to approximate the response of an extrapolation chamber. For the build‐down region, a correction factor to account for table absorption and chamber orientation in the posterior‐anterior direction was applied. The measurement depths used for the film were halfway through their sensitive volumes, and a polynomial best fit curve was used to determine the dose to their surfaces. This chamber was also compared with the dose expected in a clinical kernel‐based computer model, and a clinical Boltzmann‐transport‐equation‐based (BTE) computer model. The two models were also compared against each other for cases with air gaps in the buildup region.Results:Within 3mm, all dosimeters and models agreed with the chamber within 10% for all field sizes. At the entrance surface, film differed in comparison with the chamber from +90% to +15%, the BTE‐model by +140 to +3%, and the kernel‐based model by +20% to −25%, decreasing with increasing field size. At the exit surface, film differed in comparison with the chamber from −10% to −15%, the BTE‐model by −53% to −50%, the kernel‐based model by −55% to −57%, mostly independent of field size.Conclusion:The largest differences compared with the chamber were found at the surface for all field sizes. Differences decreased with increasing field size and increasing depth in phantom. Air gaps in the buildup region cause dose buildup to occur again post‐gap, but the effect decreases with increasing phantom thickness prior to the gap.
SU‐E‐T‐105: An FMEA Survey of Intensity Modulated Radiation Therapy (IMRT) Step and Shoot Dose Delivery Failure Modes
Authors: Faught J Tonigan , Johnson J , Stingo F , Kry S , Court L , Balter P , Followill D 
Published: June 2015

Purpose:To assess the perception of TG‐142 tolerance level dose delivery failures in IMRT and the application of FMEA process to this specific aspect of IMRT.Methods:An online survey was distributed to medical physicists worldwide that briefly described 11 different failure modes (FMs) covered by basic quality assurance in step‐ and‐shoot IMRT at or near TG‐142 tolerance criteria levels. For each FM, respondents estimated the worst case H&N patient percent dose error and FMEA scores for Occurrence, Detectability, and Severity. Demographic data was also collected.Results:181 individual and three group responses were submitted. 84% were from North America. Most (76%) individual respondents performed at least 80% clinical work and 92% were nationally certified. Respondent medical physics experience ranged from 2.5–45 years (average 18 years). 52% of individual respondents were at least somewhat familiar with FMEA, while 17% were not familiar. Several IMRT techniques, treatment planning systems and linear accelerator manufacturers were represented. All FMs received widely varying scores ranging from 1–10 for occurrence, at least 1–9 for detectability, and at least 1–7 for severity. Ranking FMs by RPN scores also resulted in large variability, with each FM being ranked both most risky (1st ) and least risky (11th) by different respondents. On average MLC modeling had the highest RPN scores. Individual estimated percent dose errors and severity scores positively correlated (p<0.10) for each FM as expected. No universal correlations were found between the demographic information collected and scoring, percent dose errors, or ranking.Conclusion:FMs investigated overall were evaluated as low to medium risk, with average RPNs less than 110. The ranking of 11 FMs was not agreed upon by the community. Large variability in FMEA scoring may be caused by individual interpretation and/or experience, thus reflecting the subjective nature of the FMEA tool.
SU‐E‐T‐106: An Institutional Review of Using Commercially Available Software to Evaluate Treatment Plan Quality for Various Treatment Sites and Beam Deliveries
Authors: Esquivel C , Patton L , Walker S , Lawson S 
Published: June 2015

Purpose:Use Sun Nuclear Quality Reports™ with PlanIQ™ to evaluate different treatment delivery techniques for various treatment sites.Methods:Fifteen random patients with different treatment sites were evaluated. These include the Head/Neck, prostate, pelvis, lung, esophagus, axilla, bladder and abdomen. Initially, these sites were planned on the Pinnacle 3 V9.6 treatment planning system and utilized nine 6MV step‐n‐shoot IMRT fields. The RT plan, dose and structure sets were sent to Quality Reports™ where a DVH was recreated and the plans were compared to a unique Plan Algorithm for each treatment site. Each algorithm has its own plan quality metrics and objectives, which include the PTV coverage, PTV maximum dose, the prescription dose outside the target, doses to the critical structures, and the global maximum dose and its location. Each plan was scored base on meeting each objective. Plans may have been reoptimized and reevaluated with Quality Reports™ based on the initial score. PlanIQ™ was used to evaluate if any objective not met was achievable or difficult to obtain. A second plan using VMAT delivery was created for each patient and scored with Quality Reports™.Results:There were a wide range of scores for the different treatment sites with some scoring better for IMRT plans and some better for the VMAT deliveries. The variation in the scores could be attributed to the treatment site, location, and shape of the target. Most deliveries were chosen for the VMAT due to the short treatment times and quick patient throughput with acceptable plan scores.Conclusion:The tools are provided for both physician and dosimetrist to objectively evaluate the use of VMAT delivery versus the step‐n‐shoot IMRT delivery for various sites. PlanIQ validates if objectives can be met. For the physicist, a concise pass/fail report is created for plan evaluation.
SU‐E‐T‐107: An Investigation Into Attenuation Effects On the Energy Spectrum for 137Cs Using Monte Carlo Techniques
Authors: Taneja S , Bartol L , Culberson W , DeWerd L 
Published: June 2015

Purpose:The calibration of radiation protection instrumentation including ionization chambers, scintillators, and Geiger Mueller (GM) counters used as survey meters are often done using 137Cs irradiators. During calibration, irradiators use a combination of attenuators with various thicknesses to modulate the beam to a known air‐kerma rate. The variations in energy spectra as a result of these attenuators are not accounted for and may play a role in the energy‐dependent response of survey meters. This study uses an experimentally validated irradiator geometry modeled in the MCNP5 transport code to characterize the effects of attenuation on the energy spectrum.Methods:A Hopewell Designs G‐10 137Cs irradiator with lead attenuators of thicknesses of 0.635, 1.22, 2.22, and 4.32 cm, was used in this study. The irradiator geometry was modeled in MCNP5 and validated by comparing measured and simulated percent depth dose (PDD) and cross‐field profiles. Variations in MCNP5 simulated spectra with increasing amounts of attenuation were characterized using the relative intensity of the 662 keV peak and the average energy.Results:Simulated and measured PDDs and profiles agreed within the associated uncertainty. The relative intensity of the 662 keV peak for simulated spectra normalized to the intensity of the unattenuated spectra ranged from 0.16% to 100% based on attenuation thickness. The average energy for simulated spectra for attenuators ranged from 582 keV with no attenuation to 653 keV with 5.54 cm of attenuation. Statistical uncertainty for MCNP5 simulations ranged from 0.11% to 3.69%.Conclusion:This study successfully used MCNP5 to validate a 137Cs irradiator geometry and characterize variations in energy spectra between different amounts of attenuation. Variations in the average energy of up to 12% were determined through simulations, and future work will aim to determine the effects of these differences on survey meter response and calibration.
SU‐E‐T‐111: An Iterative Approach to Modelling Dosimetric Properties of a Varian MLC
Authors: DiCostanzo D 
Published: June 2015

Purpose:In effort to efficiently and accurately model MLC parameters for use in Varian Eclipse treatment planning system (TPS), an iterative technique for characterizing the dosimetric properties of MLCs has been developed.Methods:The initial characterization of the dosimetric leaf gap (DLG) and MLC transmission was performed using varied sizes of moving gaps and transmission measurements through central axis of the radiation beam. These values were determined during the initial data collection. After the initial values were determined and entered into the TPS, two plans were calculated to test the veracity of DLG and transmission independently. The plan used to determine the DLG has openings of varied sizes which are affected differently by the DLG. A large field uniform fluence that required a MLC carriage shift was used to determine the transmission value independent of DLG. After characterizing the dosimetric properties of the MLC independently, clinical IMRT plans were tested and used to tweak the final values.Results:This approach to modelling MLC dosimetric properties was employed for: standard 120 leaf MLC (SDMLC) and 120 leaf high definition MLC (HDMLC). Both types were successfully commissioned, tested, and approved for clinical use on 4 SDMLC machines and 2 HDMLC machines. The pass rate of clinical IMRT plans was 96.9% for 6MV and 98.3% for 10MV for SDMLC and 96.3% for 6MV, 96.5% for 6FFF, and 97.5% for 10FFF for HDMLCs using MapCheck2 with gamma analysis of 2%/2mm and 10% threshold. The final DLG and transmission parameters for 6X were 0.5mm and 0.01, and 1.35mm and 0.02 for HD and SD MLCs respectively.Conclusion:This iterative approach of determining dosimetric properties of MLCs is viable for both SDMLC and HDMLC and multiple energies. This approach accurately and efficiently determines the values needed for commissioning MLCs when they are employed for modulated therapies.
SU‐E‐T‐112: An OpenCL‐Based Cross‐Platform Monte Carlo Dose Engine (oclMC) for Coupled Photon‐Electron Transport
Authors: Tian Z , Shi F , Folkerts M , Qin N , Jiang S , Jia X 
Published: June 2015

Purpose:Low computational efficiency of Monte Carlo (MC) dose calculation impedes its clinical applications. Although a number of MC dose packages have been developed over the past few years, enabling fast MC dose calculations, most of these packages were developed under NVidia's CUDA environment. This limited their code portability to other platforms, hindering the introduction of GPU‐based MC dose engines to clinical practice. To solve this problem, we developed a cross‐platform fast MC dose engine named oclMC under OpenCL environment for external photon and electron radiotherapy.Methods:Coupled photon‐electron simulation was implemented with standard analogue simulation scheme for photon transport and Class II condensed history scheme for electron transport. We tested the accuracy and efficiency of oclMC by comparing the doses calculated using oclMC and gDPM, a previously developed GPU‐based MC code on NVidia GPU platform, for a 15MeV electron beam and a 6MV photon beam in a homogenous water phantom, a water‐bone‐lung‐water slab phantom and a half‐slab phantom. We also tested code portability of oclMC on different devices, including an NVidia GPU, two AMD GPUs and an Intel CPU.Results:Satisfactory agreements were observed in all photon and electron cases, with ∼0.48%–0.53% average dose differences at regions within 10% isodose line for electron beam cases and ∼0.15%–0.17% for photon beam cases. It took oclMC 3–4 sec to perform transport simulation for electron beam on NVidia Titan GPU and 35–51 sec for photon beam, both with ∼0.5% statistical uncertainty. The computation was 6%–17% slower than gDPM due to the differences in both physics model and development environment, which is considered not significant for clinical applications. In terms of code portability, gDPM only runs on NVidia GPUs, while oclMC successfully runs on all the tested devices.Conclusion:oclMC is an accurate and fast MC dose engine. Its high cross‐platform portability makes it clinically attractive.