bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐316: Dosimetric Effects Resulting From Increased MLC Error and Expanded Dose Dynamic Leaf Tolerances in Sliding Window IMRT
Authors: Netherton T , Ding G 
Published: June 2015

Purpose:To examine the dosimetric effects on the target dose coverage of MLC error (actual vs. planned position) for sliding window IMRT treatment plans.Methods:Dynalog files from a treated 7 field H&N sliding window IMRT plan were imported into a Dynalog to .mlc converter. The errors of the MLC's were multiplied by factors of f= 5, 10, 50, and 500 while capping the dose dynamic leaf tolerance at 0.2cm (Eclipse TPS default). Resulting .mlc files were imported into the TPS to study the changes in dose after increasing the magnitude of MLC error. Additionally, the dose dynamic leaf tolerance was expanded to 0.3cm, 0.4cm, and 0.5cm for each case.Results:For the linac investigated, A and B MLC error was found in the direction opposite to MLC motion, toward the X1 jaw. This systematic shift in the MLC position results in a shift of the dose distribution per field when the inherent error is multiplied by a factor. The complete treatment plan had maximum and minimum dose differences (modified vs. planned) exhibiting a similar trend as individual fields with dose differences reaching 3% of the prescribed dose with f=10 and an expanded tolerance of 0.3cm.Conclusion:A clinically significant difference of 5% of the prescribed dose is seen when the MLC error is multiplied by a factor f∼15 while within the default dose dynamic leaf tolerance of 0.2cm. This suggests that if a large deviation of the MLC's from the planned positions were to occur for just 1/5 of the active leaf positions that differences in the delivered vs. planned dose per fraction could exceed 5%. Using the default MLC tolerance, no clinically significant difference in the mean target dose was found, indicating that the default MLC tolerance of 0.2cm is adequate for accurate IMRT treatment plan delivery.
SU‐E‐T‐324: Dosimetric Evaluation of Soft Docking Sensitivity On An INTRAOP Mobetron IORT Device
Authors: Carlson M , Hessler J , Grzetic S , Gupta N 
Published: June 2015

Purpose:To assess Mobetron soft docking sensitivity thresholds by measuring dosimetric changes resulting from incremental displacements of isolated docking parameters.Methods:The Mobetron device uses a sensitive optical system to establish alignment of the collimator with a treatment cone. To assess the limits of this sensitivity, we isolated each docking parameter (transverse, tilt, and vertical) and varied each incrementally within the docking display range. Transverse displacements ranged in 1mm increments from 0.0cm to 0.4cm. Profiles were taken at dmax for each energy (6MeV, 9MeV and 12MeV) along the direction of displacement. Angular displacements ranged in 0.1° increments from 0.0° to 0.4°. Baseline corrected profiles were assessed with a point‐by‐point symmetry analysis and a max‐min flatness metric (90%‐1cm). Vertical displacements ranged from 0.0cm to 0.4cm in 1mm increments. Output factors were compared by % difference from baseline and PDDs were measured at each vertical displacement to assess changes in dmax and R50 values.Results:For 1mm lateral displacements, symmetry/flatness deviations for the 10cm cone were +0.48%/+0.38% at 6MeV, +0.95%/+1.04% at 9MeV, and +1.77%/+1.96% at 12MeV. Profiles in the direction orthogonal to gantry motion measured +0.99%/+1.29% symmetry/flatness changes at 4mm displacement. For 0.10 angular displacements, symmetry/flatness deviations for the 10cm cone were +0.07%/+0.05% at 6MeV +0.23%/+0.33% at 9MeV, and +0.34%/+0.59% at 12MeV. The 3cm and 6cm cones were less sensitive to transverse and angular displacements. At 4mm vertical displacement, the 3cm cone differed from baseline by 3.02%, 2.30%, and 2.42% (6MeV, 9MeV, and 12MeV respectively). Maximum combined deviation from baseline in quadrature for one extra docking light (half sensitivity) in each displacement vector was >2%.Conclusion:For transverse and vertical displacements, the docking sensitivity range is adequate to ensure flatness and symmetry differences <1.0%. However, for angular displacements, all energies with the 10cm cone deviated at or beyond this threshold.
SU‐E‐T‐331: Dosimetric Impact of Multileaf Collimator Leaf Width On Stereotactic Radiosurgery (SRS) RapidArc Treatment Plans for Single and Multiple Brain Metastases
Authors: Hossain S , Keeling V , Ahmad S , Algan O 
Published: June 2015

Purpose:To determine the effects of multileaf collimator (MLC) leaf width on normal‐brain‐tissue doses and dose conformity of SRS RapidArc treatment plans for brain tumors.Methods:Ten patients with 24 intracranial tumors (seven with 1–2 and three with 4–6 lesions) were planned using RapidArc for both Varian Millennium 120 MLC (5 mm leaf width) and high definition (HD) MLC (2.5 mm leaf width). Between 2 and 8 arcs were used with two full coplanar arcs and the rest non‐coplanar half arcs. 6 MV beams were used and plans were optimized with a high priority to the Normal Tissue Objective (to achieve dose conformity and sharp dose fall‐off) and normal brain tissue. Calculation was done using AAA on a 1 mm grid size. The prescription dose ranged from 14–22 Gy. Plans were normalized such that 99% of the target received the prescription dose. Identical beam geometries, optimizations, calculations, and normalizations were used for both plans. Paddick Conformity Index (PCI), V4, V8 and V12 Gy for normal brain tissue and Integral Dose were used for analysis.Results:In all cases, HD MLC plans performed better in sparing normal brain tissue, achieving a higher PCI with a lower Integral Dose. The average PCI for all 24 targets was 0.75±0.23 and 0.70±0.23 (p ≤0.0015) for HD MLC and Millennium MLC plans, respectively. The average ratio of normal brain doses for Millennium MLC to HD MLC plans was 1.30±0.16, 1.27±0.15, and 1.31±0.18 for the V4, V8, and V12, respectively. The differences in normal brain dose for all criteria were statistically significant with p‐value < 0.02. On average Millennium MLC plans had a 16% higher integral dose than HD MLC plans.Conclusion:Significantly better dose conformity with reduced volume of normal brain tissue and integral dose was achieved with HD MLC plans compared to Millennium MLC plans.
SU‐E‐T‐334: Dosimetric Impacts of Organ at Risk (OAR) Contour Errors in Prostate Volumetric Modulated Arc Therapy (VMAT) Planning: A Sensitivity Study
Authors: Chang J , Gu X , Lu W , Song T , Jia X , Jiang S 
Published: June 2015

Purpose:To investigate the dosimetric impacts of OAR contour errors in prostate VMAT planning with a sensitivity analysis method.Methods:Ten randomly selected prostate VMAT patients were used to simulate OAR contour error in rectum and bladder. For each OAR 12 even spaced contour control points were selected in every three slices. For each simulation, only one of the control points was simulated to move inwards or outwards by up to 6 voxels and coordinates of adjacent voxels to that moving control point were moved accordingly with a 3D‐spline smooth function. An in‐house software was used to predict OARs dosimetric endpoints based on geometric relationship between PTV and OAR. In this study, the V75, V70, V65, V60 of rectum and V80, V75, V70, V65 of bladder with and without perturbed contours were calculated and compared.Results:The percentage of OAR dose volume difference around the reference OAR contours were plotted as iso‐error lines overlaid on CT images. The significant difference was shown in OAR contours adjacent to the PTV where high dose gradient exists. When one of the 12 points adjacent to the PTV moved up to 6 voxels, maximum errors of 1.99%, 2.46%, 2.89%, and 3.19% were found in V75, V70, V65, and V60 of the rectum, and 1.59%, 1.67%, 1.87%, and 1.90% were found in V80, V75, V70, and V65 of the bladder, respectively.Conclusion:We can quantify the dosimetric impact of OAR contouring error by evaluating the percentage of OAR dose volume changes in prostate VMAT planning. For the adaptive radiation therapy, the iso‐error lines can provide the planner a guideline that which portion of contour needed to be checked carefully because dosimetric sensitivity of contour errors are different for different part of contours.
SU‐E‐T‐345: Effect of DLG and MLC Transmission Value Set in the Treatment Planning System (TPS) On Dosimetric Accuracy of True Beam Hypofractionated SRT/SBRT and 2Gy/fx Prostate Rapid Arc Plans
Authors: Wu X , Wang Y 
Published: June 2015

Purpose:Due to limited commissioning time, we previously only released our True beam non‐FFF mode for prostate treatment. Clinical demand now pushes us to release the non‐FFF mode for SRT/SBRT treatment. When re‐planning on True beam previously treated SRT/SBRT cases on iX machine we found the patient specific QA pass rate was worse than iX's, though the 2Gy/fx prostate Result had been as good. We hypothesize that in TPS the True beam DLG and MLC transmission values, of those measured during commissioning could not yet provide accurate SRS/SBRT dosimetry. Hence this work is to investigate how the TPS DLG and transmission value affects Rapid Arc plans’ dosimetric accuracy.Methods:We increased DLG and transmission value of True beam in TPS such that their percentage differences against the measured matched those of iX's. We re‐calculated 2 SRT, 1 SBRT and 2 prostate plans, performed patient specific QA on these new plans and compared the results to the previous.Results:With DLG and transmission value set respectively 40 and 8% higher than the measured, the patient specific QA pass rate (at 3%/3mm) improved from 95.0 to 97.6% vs previous iX's 97.8% in the case of SRT. In the case of SBRT, the pass rate improved from 75.2 to 93.9% vs previous iX's 92.5%. In the case of prostate, the pass rate improved from 99.3 to 100%. The maximum dose difference in plans before and after adjusting DLG and transmission was approximately 1% of the prescription dose among all plans.Conclusion:The impact of adjusting DLG and transmission value on dosimetry might be the same among all Rapid Arc plans regardless hypofractionated or not. The large variation observed in patient specific QA pass rate might be due to the data analysis method in the QA software being more sensitive to hypofractionated plans.
SU‐E‐T‐350: Effective Point of Measurement and Total Perturbation Correction P for Parallel‐Plate Ion Chambers in High‐Energy Photon Beams
Authors: Langner N , Czarnecki D , von Voigts‐Rhetz P , Zink K 
Published: June 2015

Purpose:This paper aims to determine the effective point of measurement and the total perturbation correction p of parallel‐plate chambers for clinical photon dosimetry.Methods:The effective point of measurement (EPOM) was calculated using the EGSnrc Monte Carlo code system with the EGSnrc user code egs_ chamber. Depth dose curves of the ionization chambers were calculated in a water phantom for several high energy photon spectra (4, 6, 10, 15, 18 MV‐X). Different normalization criterions (normalization to the maximum of the depth dose curve and normalization to the value in 10 cm depth) have been applied. The EPOM was determined by shifting the normalized depth dose curve of a small water voxel against the depth ionization curve until the disagreement (calculated by the root mean square deviation) reaches a minimum. In addition, the total perturbation correction p was calculated by the ratio of the dose to water and the product of the dose determined in the chamber and the water to air stopping power ratio.Results:The EPOM varied slightly depending on the chosen normalization criterion. For all chambers the necessary shift of the EPOM decreased linearly with increasing beam quality specifier TPR20/10. For the Roos and NACP chamber, the results were positive suggesting that the chambers need to be shifted towards the focus. For the Markus chamber, the required shift was negative and for the Advanced Markus chamber partly negative and partly positive. The total perturbation correction p was almost independent of the depth. Only for regions below 1 cm the perturbation correction deviated significantly from unity.Conclusion:In the present study, the effective point of measurement and the total perturbation correction p was determined for four parallel‐plate ionization chambers and five clinical relevant photon spectra. Applying the calculated EPOM, the residual perturbation correction p was mostly depth independent.
SU‐E‐T‐358: Empirical Beam Angle Optimization for Lung Cancer Intensity Modulated Radiation Therapy
Authors: Doozan B , Pella S 
Published: June 2015

Purpose:Creating an improved BAO can decrease the amount of time a dosimetrist spends on making a treatment plan, improve the treatment quality and enhance the tools an inexperienced dosimetrist can use to develop planning techniques.Methods:Using empirical data created by experienced dosimetrists from 69 patients treated for lung cancer, the most frequently used gantry angles were applied to four different regions in each lung to gather an optimal set of fields that could be used to treat future lung cancer patients. This method, given the moniker FAU BAO, is compared in 7 plans created with the Eclipse BAO choosing 5 fields and 9 fields.Results:The results show that the conformality index improved by 30% or 3% when using the 5 and 9 fields. The conformation number was better by 12% from the 5 fields and 9% from the 9 fields. The organs at risk (OAR) were overall more protected to produce fewer nonstochastic effects from the radiation treatment with the FAU BAO.Conclusion:Empirical methods for beam angle optimization is a viable method for IMRT treatment planning techniques.
SU‐E‐T‐359: Emulation of Yb‐169 Gamma‐Ray Spectrum Using Metal‐Filtered 250 KVp X‐Rays for Pre‐Clinical Studies of Gold Nanoparticle‐Aided Radiation Therapy
Authors: Reynoso F , Cho S 
Published: June 2015

Purpose:To develop an external beam surrogate of the Yb‐169 brachytherapy source applying a filter‐based spectrum modulation technique to 250 kVp x‐rays. In‐vitro/vivo studies performed with the modulated 250 kVp beam will help gauge the benefits of implementing gold nanoparticle‐aided radiotherapy with the Yb‐169 source.Methods:A previously validated MCNP5 model of the Phillips RT‐250 orthovoltage unit was used to obtain the percentage depth dose (PDD) and filtered photon spectra for a variety of filtration and irradiation conditions. Photon spectra were obtained using the average flux F4 tally in air right after all collimation. A 30 × 30 × 30 cm3 water phantom was used to compute the PDD along the central axis (CAX) under the standards conditions of a 10 × 10 cm2 field size at 50 cm SSD. Cylindrical cells of 4 cm in diameter and the energy deposition F6 tally were used along the CAX to score the doses down to 20 cm depth. The number of particle history was set to 2 × 10⁸ in order to keep the relative uncertainty within each cell < 0.3%. The secondary electron spectrum within a gold‐loaded tissue due to each photon spectrum was also calculated using EGSnrc and compared with that due to Yb‐169 gamma rays.Results:Under the practical constraints for the spectrum modulation task, 250 kVp x‐rays filtered by a 0.25 mm Erbium (Er) foil produced the best match with Yb‐169 gamma rays, in terms of PDD and, more importantly, secondary electron spectrum.Conclusion:Modulation of 250kVp x‐ray spectrum by an Er‐filter was found effective in emulating the gamma ray spectrum of Yb‐169. Possible benefits as predicted from the current MC model such as enhanced radiosensitization with the Er‐filtered beam (as a surrogate of Yb‐169) was confirmed with a separate in‐vitro study.Supported by DOD/PCRP grant W81XWH‐12‐1‐0198
SU‐E‐T‐366: Estimation of Whole Body Dose From Cranial Irradiation From C and Perfexion Series Gamma Knife Units
Authors: Srivastava S , Andersen A , Lulu B , Cheng C , Das I 
Published: June 2015

Purpose:The Leksell Gamma Knife (GK) B & C series contains 201 Cobalt‐60 sources with a helmet. The new model, Perfexion uses 192 Cobalt‐60 sources without a helmet; using IRIS system for collimation and stereotactic guidance to deliver SRS to brain tumors. Relative dose to extracranial organs at risk (OARs) is measured in phantom in this study for Perfexion and C‐series GK.Materials & Methods:Measurements were performed in a Rando anthropomorphic phantom on both systems using a large ion chamber (Keithley‐175) for each collimator. The Keithley‐175 cc ion chamber was sandwiched between phantom slices at various locations in the phantom to correspond to different extracranial OARs (thyroid, heart, kidney, ovary and testis, etc.) The dose measurement was repeated with OSL detectors for each position and collimator.Results:A large variation is observed in the normalized dose between these two systems. The dose beyond the housing falls off exponentially for Perfexion. Dose beyond the C‐series GK housing falls off exponentially from 0–20cm then remains relatively constant from 20–40cm and again falls off with distance but less rapidly. The variation of extracranial dose with distance for each collimator is found to be parallel to each other for both systems.Conclusion:Whole body dose is found to vary significantly between these systems. It is important to measure the extracranial dose, especially for young patients. It is estimated that dose falls off exponentially from the GK housing and is about 1% for large collimators at 75 cm. The dose is two‐orders of magnitude smaller for the 4mm collimator. However, this small dose for patient may be significant radiologically.
SU‐E‐T‐372: Evaluation and Comparison of Second‐Check Monitor Unit Calculation Software with Pinnacle Treatment Planning System
Authors: Tuazon B , Narayanasamy G , Kirby N , Mavroidis P , Papanikolaou N , Stathakis S 
Published: June 2015

Purpose:The purpose of this study was to evaluate and compare the accuracy of dose calculation algorithms in the second check software programs Radcalc, Diamond, IMSure, and MUcheck, against the Pinnacle3 treatment planning system (TPS).Methods:Baseline accuracy of the second check software was established by comparison against Pinnacle TPS data using open square fields of 5, 10, 20, 30 and 40cm in a SAD setup. 18 previously treated patients’ files were exported from the Pinnacle3 TPS to each of the four second check softwares, consisting of 146 step and shoot intensity modulated radiotherapy (IMRT) beams and 60 Smart Arcs. Monitor unit (MU) calculated in each of the software were compared with the TPS and the values were represented as a percent difference. Open fields were calculated as a baseline for each software's accuracy using 5×5, 10×10, 20×20, 30×30, and 40×40 fields. Box plots, Pearson correlation, and Bland‐Altman analysis were used for comparison of the results.Results:The baseline accuracy was established to within 0.6%, −1.4%, −0.2%, and −1.0% for Diamond, IMSure,MUcheck, and Radcalc, respectively. In the clinical data, the dose difference represented as mean ± 1 standard deviation were 0.7%±0.1%, −0.3%±0.1%, −1.5%±0.1%, and 0.4%±0.0% for Diamond, IMSure, MUcheck, and Radcalc, respectivelyConclusion:The implementation of Clarkson algorithm for the dose calculation between each of the software in question can vary considerably. The currently used second check software, Radcalc has shown the best agreement on average, variance, and smallest percent range from Pinnacle3 TPS values. The closest in average percent difference from the TPS data was the IMSure software, but has significantly larger variance and percent range. The mean percent differences in Diamond and MUcheck were significantly larger than Radcalc and IMSure.
SU‐E‐T‐379: Evaluation of An EPID‐Based System for Daily Dosimetry Check by Comparison with a Widely‐Used Ionization Chamber‐Based Device
Authors: McDonald D , Koch N , Peng J , Jacqmin D , Ashenafi M , Vanek K 
Published: June 2015

Purpose:To examine the feasibility of using Varian's EPID‐based Machine Performance Check (MPC) system to track daily machine output through comparison with Sun Nuclear's DailyQA3 (DQA) device.Methods:Daily machine outputs for two photon energies (6 and 16MV) and five electron energies (6, 9, 12, 16, 20MeV) were measured for one month using both MPC and DQA. Baselines measurements for MPC were taken at the start of the measurement series, while DQA baselines were set at an earlier date. In order to make absolute comparisons with MPC, all DQA readings were referenced to the average of the first three DQA readings in that series, minimizing systematic differences between the measurement techniques due to baseline differences. In addition to daily output measurements, weekly averages were also calculated and compared. Finally, the electron energy dependence of each measurement technique was examined by comparing energy‐specific measurements to the average electron output of all energies each day.Results:For 6 and 16MV photons, the largest absolute percent differences between MPC and DQA were 0.60% and 0.73%, respectively. Weekly averages were within 0.17% and 0.23%, respectively. For all five electron energies, the greatest absolute percent differences between MPC and DQA for each energy ranged from 0.49%–0.83%. Weekly averages ranged from 0.07%–0.28%. DQA energy‐specific electron readings matched the average electron output within 0.29% for all days and all energies. MPC energy‐specific readings matched the average within 0.21% for 9–20MeV. However, 6MeV showed a larger distribution about the average with four days showing a difference greater than 0.30% and a maximum difference of 0.51%.Conclusion:MPC output measurements correlated well with the widely‐used DQA3 for most beam energies, making it a reliable back up technique for daily output monitoring. However, MPC may display an energy dependence for lower electrons energies, requiring additional investigation.
SU‐E‐T‐384: Evaluation of Dose to Medium Vs. Dose to Water Calcualtion Mode in Acuros XB Algorithm for Lung SBRT
Authors: Pokharel S , Oyewale S , Rana S 
Published: June 2015

Purpose:The purpose of this study it to evaluate the dose to medium vs. dose to water reporting mode of AcurosXB algorithm in Eclipse TPS for lung SBRTMethods:Five lung SBRT cases previously calculated with AAA algorithm have been chosen for this study. All high density materials within the body were contoured and assigned HU values. The plans were then recalculated with AcurosXB algorithm using both dose to medium (AXM) and dose to water (AXW) modes. DVHs were then calculated to quantify the differences in dosimetric indices. Also, plan differences (AXW‐AXM) and (AXW‐AXM) were computed to observe the regions where maximum dose differences occur within the body.Results:For the same plan normalization, the MU variation between the plans was within ±0.5%. All dosimetric indices of target were within ±0.5% except maximum dose to 2cm (D2‐Max) from the target. D2‐Max was consistently higher with AXW plan with a value as high as 2.71%. All the dosimetric indices for both ipsilateral and contralateral lung appear to be within ±1% on average without any clear trend. Likewise, dosimetric indices for heart and Esophagus appear well within ±1% on average. The maximum dose to spinal cord was recorded consistently higher with dose to water reporting mode with an average of 2.2% (range 1.40% to 4.63%). Also, the plan difference (AXW‐AXM) consistently produced higher maximum dose difference 8.94% (range, 4.2% to 12.4%) as opposed to 2.82%(range, 2.8% to 3.8%) from plan difference (AXM‐AXW).Conclusion:It appears that dose reporting mode in AcurosXB algorithm has insignificant effects in dosimetric indices for SBRT lung. The only significant difference observed was the maximum dose difference within the body which may not be clinically important. This may be due to the fact that AcurosXB algorithm transport the particles in medium regardless of dose reporting mode chosen.