bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐442: Geometric Calibration and Verification of a GammaPod Breast SBRT System
Authors: Yu C , Niu Y , Mutaf Y , Maton P , Hoban P 
Published: June 2015

Purpose:The first GammaPod™ unit for prone stereotactic treatment of early stage breast cancer has recently been installed and calibrated. Thirty‐six rotating circular Co‐60 beams focus dose at an isocenter that traverses throughout a breast target via continuous motion of the treatment table. The breast is immobilized and localized using a vacuum‐assisted stereotactic cup system that is fixed to the table during treatment. Here we report on system calibration and on verification of geometric and dosimetric accuracy.Methods:Spatial calibration involves setting the origin of each table translational axis within the treatment control system such that the relationship between beam isocenter and table geometry is consistent with that assumed by the treatment planning system. A polyethylene QA breast phantom inserted into an aperture in the patient couch is used for calibration and verification. The comparison is performed via fiducial‐based registration of measured single‐isocenter dose profiles (radiochromic film) with kernel dose profiles. With the table calibrations applied, measured relative dose distributions were compared with TPS calculations for single‐isocenter and dynamic (many‐isocenter) treatment plans. Further, table motion accuracy and linearity was tested via comparison of planned control points with independent encoder readouts.Results:After table calibration, comparison of measured and calculated single‐isocenter dose profiles show agreement to within 0.5 mm for each axis. Gamma analysis of measured vs calculated profiles with 3%/2mm criteria yields a passing rate of >99% and >98% for single‐isocenter and dynamic plans respectively. This also validates the relative dose distributions produced by the TPS. Measured table motion accuracy was within 0.05 mm for all translational axes.Conclusion:GammaPod table coordinate calibration is a straightforward process that yields very good agreement between planned and measured relative dose distributions. The dynamic table motions used for dose painting are consistent with planned control points.CY, YN, PM, PH are employees of Xcision Medical Systems
SU‐E‐T‐443: Geometric Uncertainties in Eye Plaque Dosimetry for a Fully Loaded 16 Mm COMS Plaque
Authors: Morrison H , Menon G , Jans H , Larocque M , Sloboda R 
Published: June 2015

Purpose:To determine the effect of geometric uncertainties in the seed positions in a COMS eye plaque on the central axis (CAX) dose.Methods:A Silastic insert was placed into a photopolymer 3D printed 16 mm COMS plaque, which was then positioned onto a custom‐designed PMMA eye phantom. High resolution 3D images were acquired of the setup using a Siemens Inveon microPET/CT scanner. Images were acquired with the plaque unloaded and loaded with IsoAid I‐125 seed shells (lack of silver core to minimize metal artifacts). Seed positions and Silastic thickness beneath each slot were measured. The measured seed coordinates were used to alter the seed positions within a standard 16 mm COMS plaque in Plaque Simulator v5.7.3 software. Doses along the plaque CAX were compared for the original and modified plaque coordinates using 3.5 mCi seeds with treatment times set to deliver 70 Gy to tumour apexes of 3.5, 5, and 10 mm height.Results:The majority of seeds showed length‐wise displacement, and all seeds showed displacement radially outward from the eye center. The average radial displacement was 0.15 mm larger than the expected 1.4 mm offset, approximately half of which was due to increased Silastic thickness beneath each slot. The CAX doses for the modified seed positions were consistently lower for all tumour heights due to geometric displacement of the seeds; dose differences were found to increase to a maximum of 2.6% at a depth of ∼10 mm, after which they decreased due to the inverse square dose fall‐off minimizing this effect.Conclusion:This work presents initial results of a broader dosimetric uncertainty evaluation for fully loaded COMS eye plaques and demonstrates the effects of seed positioning uncertainties. The small shifts in seed depths had noticeable effects on the CAX doses indicating the importance of careful Silastic loading.Funding provided by Alberta Cancer Foundation Grant #26655, Vanier Canada Graduate Scholarship, and Alberta Innovates Health Sciences Graduate Studentship
SU‐E‐T‐444: Gravity Effect On Maximum Leaf Speed in Dynamic IMRT Treatments
Authors: Olasolo J , Pellejero S , Artacho JM , Gracia M , Gallardo N , Martin ML , Lozares S , Maneru F , Bragado L , Miquelez S 
Published: June 2015

Purpose:A leaf sequencing algorithm has been recently developed in our department. Our purpose is to utilize this algorithm to reduce treatment time by studying the feasibility of using several maximum leaf speeds depending on gantry angle and leaf thickness (0.5 or 1 cm at isocenter). To do so, the gravity effect on MLC performance has been examined by means of analysing the dynalog files.Methods:Leaf position errors has been ascertained according to gantry angle and leaf speed in MLC Millenium120 (Varian). In order to do this, the following test has been designed: all leaves move in synchrony, with same speed and 1 cm gap between opposite leaves. This test is implemented for 18 different speeds: 0.25‐0.5‐0.75‐1‐1.25‐1.5‐1.75‐2‐2.1‐2.2‐2.3‐2.4‐2.5‐2.6‐2.7‐2.8‐2.9‐3.0 cm/s and 8 gantry angles: 0‐45‐90‐135‐180‐225‐270‐315. Collimator angle is 2 degrees in all cases since it is the most usual one in IMRT treatments in our department. Dynamic tolerance is 2 mm. Dynalogs files of 10 repetitions of the test are analysed with a Mathlab in‐house developed software and RMS error and 95th percentiles are calculated. Varian recommends 2.5 cm/s as the maximum leaf speed for its segmentation algorithm. In our case, we accept this speed in the most restrictive situation: gantry angle 270 and 1 cm leaf thickness. Maximum speeds for the rest of the cases are calculated by keeping the difference between 95th percentile and dynamic tolerance. In this way, beam hold‐off probability does not increase.Results:Maximum speeds every 45 degrees of gantry rotation have been calculated for both leaf thickness. These results are 2.9‐2.9‐2.9‐2.9‐2.7‐2.6‐2.6‐2.7 cm/s for 0.5 cm leaf thickness and 2.7‐2.7‐2.7‐2.7‐2.6‐2.5‐2.5‐2.6 cm/s for 1 cm leaf thickness.Conclusion:Gravity effect on MLC positioning has been studied. Maximum leaf speed according to leaf thickness and gantry angle have been calculated which reduces treatment time.
SU‐E‐T‐446: Group‐Sparsity Based Angle Generation Method for Beam Angle Optimization
Authors: Gao H 
Published: June 2015

Purpose:This work is to develop the effective algorithm for beam angle optimization (BAO), with the emphasis on enabling further improvement from existing treatment‐dependent templates based on clinical knowledge and experience.Methods:The proposed BAO algorithm utilizes a priori beam angle templates as the initial guess, and iteratively generates angular updates for this initial set, namely angle generation method, with improved dose conformality that is quantitatively measured by the objective function. That is, during each iteration, we select “the test angle” in the initial set, and use group‐sparsity based fluence map optimization to identify “the candidate angle” for updating “the test angle”, for which all the angles in the initial set except “the test angle”, namely “the fixed set”, are set free, i.e., with no group‐sparsity penalty, and the rest of angles including “the test angle” during this iteration are in “the working set”. And then “the candidate angle” is selected with the smallest objective function value from the angles in “the working set” with locally maximal group sparsity, and replaces “the test angle” if “the fixed set” with “the candidate angle” has a smaller objective function value by solving the standard fluence map optimization (with no group‐sparsity regularization). Similarly other angles in the initial set are in turn selected as “the test angle” for angular updates and this chain of updates is iterated until no further new angular update is identified for a full loop.Results:The tests using the MGH public prostate dataset demonstrated the effectiveness of the proposed BAO algorithm. For example, the optimized angular set from the proposed BAO algorithm was better the MGH template.Conclusion:A new BAO algorithm is proposed based on the angle generation method via group sparsity, with improved dose conformality from the given template.Hao Gao was partially supported by the NSFC (#11405105), the 973 Program (#2015CB856000) and the Shanghai Pujiang Talent Program (#14PJ1404500).
SU‐E‐T‐448: Heightened Apical Positivity of 2‐Year Post‐Radiotherapy Biopsies Is Not Related to Suboptimal Dosimetry
Authors: Studenski M , Stoyanova R , Abramowitz M , Dogan N , Pollack A 
Published: June 2015

Purpose:Previous research has demonstrated that following radiation therapy for prostate cancer, there is a relative increase in positive biopsies in the apex versus the rest of the prostate. The increase could be due to: 1) Inter‐fraction apex motion or deformation, 2) Intra‐fraction apex motion or deformation, 3) Suboptimal dose coverage in the apex, 4) Tissue composition in the apex and/or 5) Prostate size. In this initial study, the potential for suboptimal dose coverage in the apex was assessed by splitting the prostate planning target volume into the apex (inferior third) and remainder.Methods:69 patients were selected from 303 patients treated on a clinical radiotherapy trial for prostate cancer. These patients were selected as they had both a localized (sextant template) 2‐year post‐treatment biopsy and 3D dose information. Of these patients, 10 had positive biopsies in the apex, 8 in the remainder and 11 in both locations. For all patients, the following dosimetric data was acquired from the apex dose volume histogram: Dmean, Dmax, Dmin, D95% and V100%. Unpaired, one‐tailed t‐tests were used to test for statistical significance (p < 0.05) between all dosimetric parameters for patients with positive versus negative apical biopsies. Additionally, D95% for the apex was plotted against D95% of the remainder.Results:There was no statistical difference for the selected apical dosimetric parameters for patients with positive versus negative biopsies (p‐values > 0.05). No correlation was found between D95% (normalized to the prescription dose) for the apex and remainder (R2 = 0.0116).Conclusion:No correlation was found between positive apical biopsy and suboptimal dosimetric coverage. Current research is looking into inter‐fraction apex motion and deformation as a potential source of the increased apical failure using daily CBCT images.
SU‐E‐T‐451: Hybrid‐VMAT: A Novel Technique Combining VMAT and 3D in Planning Whole Breast Radiotherapy with a Simultaneously‐Integrated Boost (WBRT+SIB)
Authors: Guida K , Qamar K , Thompson M 
Published: June 2015

Purpose:The RTOG 1005 trial offered a hypofractionated arm in delivering WBRT+SIB. Traditionally, treatments were planned at our institution using field‐in‐field (FiF) tangents with a concurrent 3D conformal boost. With the availability of VMAT, it is possible that a hybrid VMAT‐3D planning technique could provide another avenue in treating WBRT+SIB.Methods:A retrospective study of nine patients previously treated using RTOG 1005 guidelines was performed to compare FiF+3D plans with the hybrid technique. A combination of static tangents and partial VMAT arcs were used in base‐dose optimization. The hybrid plans were optimized to deliver 4005cGy to the breast PTVeval and 4800cGy to the lumpectomy PTVeval over 15 fractions. Plans were optimized to meet the planning goals dictated by RTOG 1005.Results:Hybrid plans yielded similar coverage of breast and lumpectomy PTVs (average D95 of 4013cGy compared to 3990cGy for conventional), while reducing the volume of high dose within the breast; the average D30 and D50 for the hybrid technique were 4517cGy and 4288cGy, compared to 4704cGy and 4377cGy for conventional planning. Hybrid plans increased conformity as well, yielding CI95% values of 1.22 and 1.54 for breast and lumpectomy PTVeval volumes; in contrast, conventional plans averaged 1.49 and 2.27, respectively. The nearby organs at risk (OARs) received more low dose with the hybrid plans due to low dose spray from the partial arcs, but all hybrid plans did meet the acceptable constraints, at a minimum, from the protocol. Treatment planning time was also reduced, as plans were inversely optimized (VMAT) rather than forward optimized.Conclusion:Hybrid‐VMAT could be a solution in delivering WB+SIB, as plans yield very conformal treatment plans and maintain clinical standards in OAR sparing. For treating breast cancer patients with a simultaneously‐integrated boost, Hybrid‐VMAT offers superiority in dosimetric conformity and planning time as compared to FIF techniques.
SU‐E‐T‐452: Identifying Inefficiencies in Radiation Oncology Workflow and Prioritizing Solutions for Process Improvement and Patient Safety
Authors: Bennion N , Driewer J , Jacobs K , Poole M , McMahon R , Wilson K , Denniston K , Zhen W , Yager A , Enke C 
Published: June 2015

Purpose:Successful radiation therapy requires multi‐step processes susceptible to unnecessary delays that can negatively impact clinic workflow, patient satisfaction, and safety. This project applied process improvement tools to assess workflow bottlenecks and identify solutions to barriers for effective implementation.Methods:We utilized the DMAIC (define, measure, analyze, improve, control) methodology, limiting our scope to the treatment planning process. From May through December of 2014, times and dates of each step from simulation to treatment were recorded for 507 cases. A value‐stream map created from this dataset directed our selection of outcome measures (Y metrics). Critical goals (X metrics) that would accomplish the Y metrics were identified. Barriers to actions were binned into control‐impact matrices, in order to stratify them into four groups: in/out of control and high/low impact. Solutions to each barrier were then categorized into benefit‐effort matries to identify those of high benefit and low effort.Results:For 507 cases, the mean time from simulation to treatment was 235 total hours. The mean process and wait time were 60 and 132 hours, respectively. The Y metric was to increase the ratio of all non‐emergent plans completed the business day prior to treatment from 47% to 75%. Project X metrics included increasing the number of IMRT QAs completed at least 24 hours prior to treatment from 19% to 80% and the number of non‐IMRT plans approved at least 24 hours prior to treatment from 33% to 80%. Intervals from simulation to target contour and from initial plan completion to plan approval were identified as periods that could benefit from intervention. Barriers to actions were binned into control‐impact matrices and solutions by benefit‐effort matrices.Conclusion:The DMAIC method can be successfully applied in radiation therapy clinics to identify inefficiencies and prioritize solutions for the highest impact.
SU‐E‐T‐453: Image‐Guided Patient‐Specific Quality Assurance for Multi‐Target Single Isocenter Intracranial VMAT Radiosurgery
Authors: Huang M , Brezovich I , Duan J , Wu X , Shen S , Cardan R. , Fiveash J , Popple R 
Published: June 2015

Purpose:To demonstrate a patient specific, image‐guided quality assurance method that tests both dosimetric and geometric accuracy for single‐isocenter multiple‐target VMAT radiosurgery (SIMT‐VMAT‐SRS)Method:We used a new film type, EBT‐XD (optimal range 0.4–40Gy), and an in‐house PMMA phantom having a coronal plane for film and a 0.125 cm3 ionization chamber (IC). The phantom contained fiducial features for kV image guided setup and for accurate film marking. Five patient plans with multiple targets sizes ranging from 3 to 21mm in diameter and prescribed doses from 14 to 18 Gy were selected. Two verification plans were generated for each case with the film plane passing through the center of the largest and smallest targets. For the four largest targets we obtained an IC measurement. For each case, a calibration film was irradiated using a custom designed step pattern. The films were scanned using a flatbed color scanner and converted to dose using the calibration film and the three channel calibration method. Image registration was performed between film and treatment planning system calculations to evaluate the geometric accuracy.Results:The mean registration vector had an average magnitude of 0.47 mm (range from 0.13mm to 0.64 mm). For the four largest targets, the mean ratio of the IC and film measurement to expected dose was 0.990 (range 0.968 to 1.009) and 1.032 (1.021 to 1.046), respectively. The fraction of pixels having gamma index < 1 for criteria of 3%/3mm, 3%/2mm, 3%/1mm was 98.8%, 97.5% and 87.2% before geometric registration and 99.1%, 98.3% and 94.8% after registration.Conclusion:We have demonstrated an image‐guided QA method can assess both geometric and dosimetric accuracy. The phantom was positioned with sub‐millimeter accuracy. Absolute film dosimetry using EBT‐XD film was sufficiently accurate for assessment of dose to multi‐targets too small for IC measurement in SRS VMAT plans.
SU‐E‐T‐456: Impact of Dose Calculation Algorithms On Biologically Optimized VMAT Plans for Esophageal Cancer
Authors: Thiyagarajan Rajesh , Nambiraj N Arunai , Vikraman S , Karrthick KP , Sigamani Ashokkumar , Subbarao Bargavan , Ramu M , Sambasivaselli R , Senniandavar V , Kataria Tejinder 
Published: June 2015

Purpose:To evaluate the impact of dose calculation algorithm on the dose distribution of biologically optimized Volumatric Modulated Arc Therapy (VMAT) plans for Esophgeal cancer.Methods:Eighteen retrospectively treated patients with carcinoma esophagus were studied. VMAT plans were optimized using biological objectives in Monaco (5.0) TPS for 6MV photon beam (Elekta Infinity). These plans were calculated for final dose using Monte Carlo (MC), Collapsed Cone Convolution (CCC) & Pencil Beam Convolution (PBC) algorithms from Monaco and Oncentra Masterplan TPS. A dose grid of 2mm was used for all algorithms and 1% per plan uncertainty maintained for MC calculation. MC based calculations were considered as the reference for CCC & PBC. Dose volume histogram (DVH) indices (D95, D98, D50 etc) of Target (PTV) and critical structures were compared to study the impact of all three algorithms.Results:Beam models were consistent with measured data. The mean difference observed in reference with MC calculation for D98, D95, D50 & D2 of PTV were 0.37%, −0.21%, 1.51% & 1.18% respectively for CCC and 3.28%, 2.75%, 3.61% & 3.08% for PBC. Heart D25 mean difference was 4.94% & 11.21% for CCC and PBC respectively. Lung Dmean mean difference was 1.5% (CCC) and 4.1% (PBC). Spinal cord D2 mean difference was 2.35% (CCC) and 3.98% (PBC). Similar differences were observed for liver and kidneys. The overall mean difference found for target and critical structures was 0.71±1.52%, 2.71±3.10% for CCC and 3.18±1.55%, 6.61±5.1% for PBC respectively.Conclusion:We observed a significant overestimate of dose distribution by CCC and PBC as compared to MC. The dose prediction of CCC is closer (<3%) to MC than that of PBC. This can be attributed to poor performance of CCC and PBC in inhomogeneous regions around esophagus. CCC can be considered as an alternate in the absence of MC algorithm.
SU‐E‐T‐457: Impact of Interfractional Variations On Anterior Vs. Lateral‐Field Proton Therapy of Prostate Cancer
Authors: Moteabbed M , Trofimov A , Sharp G C , Wang Y , Zietman A L , Efstathiou J A , Lu H 
Published: June 2015

Purpose:To investigate the effects of interfractional anatomy and setup variations on plans with anterior‐oblique vs. lateral beams for prostate cancer pencil beam scanning (PBS) and passive scattered (PS) proton therapy.Methods:Six patients with low/intermediate risk prostate cancer treated with PS proton therapy at our institution were selected. All patients underwent weekly verification CT scans. Implanted fiducials were used for localization, and endorectal balloons for prostate immobilization. New PBS plans with lateral beams, as well as PBS and PS plans with anterior‐oblique beams (±35 deg) were created. PBS plans used two different spot sizes: ∼10mm (large) and ∼5mm (medium) sigma at 25cm range and optimized as single‐field‐uniform‐dose with ∼8% non‐uniformity. No range uncertainty margins were applied in PBS plans to maximize rectal sparing. Field‐specific apertures were used when planning with large spots to sharpen the penumbrae. The planned dose was recomputed on each weekly CT with fiducials aligned to the simulation CT, scaled and accumulated via deformable image registration.Results:The dose volume analysis showed that although difference between planned and accumulated dose remains negligible for plans with conventional lateral beams using both PS and PBS, this is not the case for plans with anterior beams. The target coverage in anterior plans was largely degraded due to the variations in the beam path length and the absence of range margins. The average prostate D95 was reduced by 7.5/15.9% (using PS/PBS) after accumulation for anterior plans, compared with 0/0.4% for lateral plans. The average mean dose in organs‐at‐risk decreased by 1% for lateral and 2% for anterior plans, similarly for PS and PBS. Spot size did not affect the dose changes.Conclusion:Prostate plans using anterior beams may undergo clinically relevant interfractional dose degradation. Corrective strategies guided by in‐vivo range measurements should be studied before clinical application of this technique.
SU‐E‐T‐459: Impact of Source Position and Traveling Time On HDR Skin Surface Applicator Dosimetry
Authors: Jeong J , Barker C , Zaider M , Cohen G 
Published: June 2015

Purpose:Observed dosimetric discrepancy between measured and treatment planning system (TPS) predicted values, during applicator commissioning, were traced to source position uncertainty in the applicator. We quantify the dosimetric impact of this geometric uncertainty, and of the source traveling time inside the applicator, and propose corrections for clinical use.Methods:We measured the dose profiles from the Varian Leipzig‐style (horizontal) HDR skin applicator, using EBT3 film, photon diode, and optically stimulated luminescence dosimeter (OSLD) and three different GammaMed HDR afterloders. The dose profiles and depth dose of each aperture were measured at several depths (up to about 10 mm, depending on the dosimeter). The measured dose profiles were compared with Acuros calculated profiles in BrachyVision TPS. For the impact of the source position, EBT3 film measurements were performed with applicator, facing‐down and facing‐up orientations. The dose with and without source traveling was measured with diode detector using HDR timer and electrometer timer, respectively.Results:Depth doses measured using the three dosimeters were in good agreement, but were consistently higher than the Acuros dose calculations. Measurements with the applicator facing‐up were significantly lower than those in the facing‐down position with maximum difference of about 18% at the surface, due to source sag inside the applicator. Based on the inverse‐square law, the effective source sag was evaluated to be about 0.5 mm from the planned position. The additional dose from the source traveling was about 2.8% for 30 seconds with 10 Ci source, decreasing with increased dwelling time and decreased source activity.Conclusion:Due to the short source‐to‐surface distance of the applicator, the small source sag inside the applicator has significant dosimetric impact, which should be considered before the clinical use of the applicator. Investigation of the effect for other applicators that have relatively large source lumen inner diameter may be warranted.Christopher Barker and Gil'ad Cohen are receiving research support for a study of skin surface brachytherapy from Elekta.