bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐815: In Vivo Dosimetry and Daily Arc Junction Verification Using EBT3 Gafchromic Film for Pediatric Cranio‐Spinal Irradiation
Authors: Saleh H , Ferjani S , Masssey V , Howlin T , Pokhrel D 
Published: June 2015

Purpose:Perform dosimetric comparison between planned and delivered dose in the junction area, measure daily dose variation in the arc junction area for pediatric patients treated for medulloblastoma using Craniospinal axis irradiation(CSI)Material and methodsDose comparison in the junction area, daily dose variation in the arc junction area for a Rando Phantom and 5 pediatric patients treated using CSI technique were analyzed. Plans were created using the Eclipse treatment planning system. Two arcs for cranium and 1 arc for spine region were used. Planar dose matrix was created by projecting phantom and patient plan into the ArcCheck phantom. EBT3 film was placed in the middle of ArcCheck plug to measure dose distribution in the junction areaDuring patient treatment, strip of EBT3 film was placed daily at each junction area for verification. EBT3 films were scanned using a flatbed scanner, Epson Expression 10000 XL. Film QA pro software was used to analyze film. Scanning and analysis was performed according to vendor recommendations and AAPM TG‐55 report. Films were scanned and analyzed daily after each treatment and at the end of treatment course. Planar dose distributions from films were compared with planar dose distribution from treatment planning system.Results:Comparison of planned vs. measured dose distributions for patients have passing rates of 90%–100% with 3% and 3 mm gamma analysis. In some of the treatment fractions, daily setup film showed variation in dose distribution in the junction area.Conclusion:It is critical to measure dose distribution in the arc junction area and use additional quality assurance measures to verify daily setup for CSI patient where one or more junctions are present. EBT3 film prove to be a good tool to achieve this task considering flexibility associated with the film such as symmetry, self‐developing and ease of use
SU‐F‐BRD‐07: Fast Monte Carlo‐Based Biological Optimization of Proton Therapy Treatment Plans for Thyroid Tumors
Authors: Wan Chan Tseung H , Ma J , Ma D , Beltran C 
Published: June 2015

Purpose:To demonstrate the feasibility of fast Monte Carlo (MC) based biological planning for the treatment of thyroid tumors in spot‐scanning proton therapy.Methods:Recently, we developed a fast and accurate GPU‐based MC simulation of proton transport that was benchmarked against Geant4.9.6 and used as the dose calculation engine in a clinically‐applicable GPU‐accelerated IMPT optimizer. Besides dose, it can simultaneously score the dose‐averaged LET (LETd), which makes fast biological dose (BD) estimates possible. To convert from LETd to BD, we used a linear relation based on cellular irradiation data. Given a thyroid patient with a 93cc tumor volume, we created a 2‐field IMPT plan in Eclipse (Varian Medical Systems). This plan was re‐calculated with our MC to obtain the BD distribution. A second 5‐field plan was made with our in‐house optimizer, using pre‐generated MC dose and LETd maps. Constraints were placed to maintain the target dose to within 25% of the prescription, while maximizing the BD. The plan optimization and calculation of dose and LETd maps were performed on a GPU cluster. The conventional IMPT and biologically‐optimized plans were compared.Results:The mean target physical and biological doses from our biologically‐optimized plan were, respectively, 5% and 14% higher than those from the MC re‐calculation of the IMPT plan. Dose sparing to critical structures in our plan was also improved. The biological optimization, including the initial dose and LETd map calculations, can be completed in a clinically viable time (∼30 minutes) on a cluster of 25 GPUs.Conclusion:Taking advantage of GPU acceleration, we created a MC‐based, biologically optimized treatment plan for a thyroid patient. Compared to a standard IMPT plan, a 5% increase in the target's physical dose resulted in ∼3 times as much increase in the BD. Biological planning was thus effective in escalating the target BD.
SU‐F‐BRD‐08: A Novel Technique to Derive a Clinically‐Acceptable Beam Model for Proton Pencil‐Beam Scanning in a Commercial Treatment Planning System
Authors: Scholey J. E. , Lin L. , Ainsley C. G. 
Published: June 2015

Purpose:To evaluate the accuracy and limitations of a commercially‐available treatment planning system's (TPS's) dose calculation algorithm for proton pencil‐beam scanning (PBS) and present a novel technique to efficiently derive a clinically‐acceptable beam model.Methods:In‐air fluence profiles of PBS spots were modeled in the TPS alternately as single‐(SG) and double‐Gaussian (DG) functions, based on fits to commissioning data. Uniform‐fluence, single‐energy‐layer square fields of various sizes and energies were calculated with both beam models and delivered to water. Dose was measured at several depths. Motivated by observed discrepancies in measured‐versus‐calculated dose comparisons, a third model was constructed based on double‐Gaussian parameters contrived through a novel technique developed to minimize these differences (DGC). Eleven cuboid‐dose‐distribution‐shaped fields with varying range/modulation and field size were subsequently generated in the TPS, using each of the three beam models described, and delivered to water. Dose was measured at the middle of each spread‐out Bragg peak.Results:For energies <160 MeV, the DG model fit square‐field measurements to <2% at all depths, while the SG model could disagree by >6%. For energies >160 MeV, both SG and DG models fit square‐field measurements to <1% at <4 cm depth, but could exceed 6% deeper. By comparison, disagreement with the DGC model was always <3%. For the cuboid plans, calculation‐versus‐measured percent dose differences exceeded 7% for the SG model, being larger for smaller fields. The DG model showed <3% disagreement for all field sizes in shorter‐range beams, although >5% differences for smaller fields persisted in longer‐range beams. In contrast, the DGC model predicted measurements to <2% for all beams.Conclusion:Neither the TPS's SG nor DG models, employed as intended, are ideally suited for routine clinical use. However, via a novel technique to be presented, its DG model can be tuned judiciously to yield acceptable results.
SU‐F‐BRD‐12: When Does Pencil Beam Scanning Become Superior to Passive Scattered Proton Therapy for Pediatric Head and Neck Cancers?
Authors: Moteabbed M , Depauw N , Kooy H , Yock T , Paganetti H 
Published: June 2015

Purpose:To investigate the dosimetric benefits of pencil beam scanning (PBS) compared with passive scattered (PS) proton therapy for treatment of pediatric head&neck patients as a function of the PBS spot size and explore the advantages of using apertures in PBS.Methods:Ten pediatric patients with head&neck cancers treated by PS proton therapy at our institution were retrospectively selected. The histologies included rhabdomyosarcoma, ependymoma, astrocytoma, craniopharyngioma and germinoma. The prescribed dose ranged from 36 to 54 Gy(RBE). Five PBS plans were created for each patient using variable spot size (average sigma at isocenter) and choice of beam specific apertures: (1) 10mm spots, (2) 10mm spots with apertures, (3) 6mm spots, (4) 6mm spots with apertures, and (5) 3mm spots. The plans were optimized for intensity modulated proton therapy (IMPT) with no single beam uniformity constraints. Dose volume indices as well as equivalent uniform dose (EUD) were compared between PS and PBS plans.Results:Although target coverage was clinically adequate for all cases, the plans with largest (10mm) spots provide inferior quality compared with PS in terms of dose to organs‐at‐risk (OAR). However, adding apertures to these plans ensured lower OAR dose than PS. The average EUD difference between PBS and PS plans over all patients and organs at risk were (1) 2.5%, (2) −5.1%, (3) ‐5%, (4) −7.8%, and (5) −9.5%. As the spot size decreased, more conformal plans were achieved that offered similar target coverage but lower dose to the neighboring healthy organs, while alleviating the need for using apertures.Conclusion:The application of PBS does not always translate to better plan qualities compared to PS depending on the available beam spot size. We recommend that institutions with spot size larger than ∼6mm at isocenter consider using apertures to guarantee clinically comparable or superior dosimetric efficacy to PS treatments.
SU‐F‐BRD‐14: Dose Weighted Linear Energy Transfer Analysis of Critical Structures in Proton Therapy of Pediatric Brain Tumor Patients
Authors: Pirlepesov F. , Shin J. , Moskvin V. P. , Gray J. , Li Z. , Hua C. , Gajjar A. , Krasin M. J. , Merchant T. E. , Farr J. B. 
Published: June 2015

Purpose:Dose weighted Linear Energy Transfer (LETd) analysis of critical structures may be useful in understanding the side effects of the proton therapy. The objective is to analyze the differences between LETd and dose distributions in brain tumor patients receiving double scattering proton therapy, to quantify LETd variation in critical organs, and to identify beam arrangements contributing to high LETd in critical organs.Methods:Monte Carlo simulations of 9 pediatric brain tumor patients were performed. The treatment plans were reconstructed with the TOPAS Monte Carlo code to calculate LETd and dose. The beam data were reconstructed proximal to the aperture of the double scattering nozzle. The dose and LETd to target and critical organs including brain stem, optic chiasm, lens, optic nerve, pituitary gland, and hypothalamus were computed for each beam.Results:Greater variability in LETd compared to dose was observed in the brainstem for patients with a variety of tumor types including 5 patients with tumors located in the posterior fossa. Approximately 20%–44% brainstem volume received LETd of 5kev/µm or greater from beams within gantry angles 180°±30° for 5 patients treated with a 3 beam arrangement. Critical organs received higher LETd when located in the vicinity of the beam distal edge.Conclusion:This study presents a novel strategy in the evaluation of the proton treatment impact on critical organs. While the dose to critical organs is confined below the required limits, the LETd may have significant variation. Critical organs in the vicinity of beam distal edge receive higher LETd and depended on beam arrangement, e.g. in posterior fossa tumor treatment, brainstem receive higher LETd from posterior‐anterior beams. This study shows importance of the LETd analysis of the radiation impact on the critical organs in proton therapy and may be used to explain clinical imaging observations after therapy.
SU‐F‐BRD‐16: Relative Biological Effectiveness of Double‐Strand Break Induction for Modeling Cell Survival in Pristine Proton Beams of Different Dose‐Averaged Linear Energy Transfers
Authors: Peeler C , Taleei R , Guan F , Bronk L , Patel D , Titt U , Mirkovic D , Stewart R , Grosshans D , Mohan R 
Published: June 2015

Purpose:High throughput in vitro experiments assessing cell survival following proton radiation indicate that both the alpha and the beta parameters of the linear quadratic model increase with increasing proton linear energy transfer (LET). We investigated the relative biological effectiveness (RBE) of double‐strand break (DSB) induction as a means of explaining the experimental results.Methods:Experiments were performed with two lung cancer cell lines and a range of proton LET values (0.94 – 19.4 keV/µm) using an experimental apparatus designed to irradiate cells in a 96 well plate such that each column encounters protons of different dose‐averaged LET (LETd). Traditional linear quadratic survival curve fitting was performed, and alpha, beta, and RBE values obtained. Survival curves were also fit with a model incorporating RBE of DSB induction as the sole fit parameter. Fitted values of the RBE of DSB induction were then compared to values obtained using Monte Carlo Damage Simulation (MCDS) software and energy spectra calculated with Geant4. Other parameters including alpha, beta, and number of DSBs were compared to those obtained from traditional fitting.Results:Survival curve fitting with RBE of DSB induction yielded alpha and beta parameters that increase with proton LETd, which follows from the standard method of fitting; however, relying on a single fit parameter provided more consistent trends. The fitted values of RBE of DSB induction increased beyond what is predicted from MCDS data above proton LETd of approximately 10 keV/µm.Conclusion:In order to accurately model in vitro proton irradiation experiments performed with high throughput methods, the RBE of DSB induction must increase more rapidly than predicted by MCDS above LETd of 10 keV/µm. This can be explained by considering the increased complexity of DSBs or the nature of intra‐track pairwise DSB interactions in this range of LETd values.NIH Grant 2U19CA021239‐35
SU‐F‐BRB‐01: How Effective Is Abdominal Compression at Reducing Lung Motion? An Analysis Using Deformable Image Registration Within Different Sub‐Regions of the Lung
Authors: Paradiso D , Pearce A , Leszczynski K , Oliver M 
Published: June 2015

Purpose:To investigate the effectiveness of employing abdominal compression (AC) in reducing motion for the target region and sub‐regions of the lung as part of the planning process for radiation therapy.Methods:Fourteen patients with early lung cancer were scanned with 4DCT and it was determined that target motion exceeded our institutional limit of > 8 mm motion and received a repeat 4DCT with AC. For each 4DCT, deformable image registration (DIR) was used to map the max inhale to the max exhale phase to determine the deformation vector fields (DVF). DIR was performed with Morphons and Demons algorithms. The mean DVF was used to represent that sub‐region for each patient. The magnitudes of the mean DVF were quantified for the target and 12 sub‐regions in the AP, LR SI directions. The sub‐regions were contoured on each lung as (add prefix R or L for lung): Upper‐Anterior (UA), Upper‐Posterior (UP), Mid‐Anterior (MA), Mid‐Posterior (MP), Lower‐Anterior (LA) and Lower‐Posterior (LP).Results:The min/max SI motion for the target on the uncompressed 4DCT was 8mm/24.5 mm. The magnitude of decrease in SI was greatest in the RLP region (3.7±4.0mm) followed by target region (3.3±2.2mm) and finally the LLP region (3.0±3.5mm). The magnitude of decrease in 3D vector followed the same trend; RLP (3.5±2.2mm) then GTV (3.5±2.6mm) then LLP (2.7±3.8mm). 79% of the cases had a SI decrease of >12.5%, 43% had a SI decrease of >25% and 21% had a SI decrease of >50% as compared to the motion on the uncompressed 4DCT.Conclusion:AC is useful in reducing motion with the largest decreases observed in the lower posterior regions of the lungs. However, it should be noted that AC will not greatly decrease motion for all cases as 21% of cases did not reduce SI motion more than 12.5% of initial motion.
SU‐F‐BRB‐09: Measurement Based Dose‐Volume Metrics for the Quality Assurance of VMAT Plans‐Are We There Yet?
Authors: Arumugam S , Xing A , Young T , Blake S , Thwaites D , Holloway L 
Published: June 2015

Purpose:To validate ArcCHECK measurement‐based 3DVH dose‐volume metrics for use with volumetric modulated arc therapy (VMAT) plans.Methods:Five each of prostate and head and neck (H&N) VMAT plans were considered for this study. Three types of errors were introduced into the original plans: gantry angle independent MLC shift (ranging from −5mm to 5mm), gantry angle dependent MLC error (ranging from 1mm to 7mm) and gantry angle dependent dose error (ranging from 1% to 10%). The percentage difference in PTV‐D95 as estimated by 3DVH for the error‐introduced delivery was compared with a similar metric calculated by comparing the dose matrices of the error‐free and error‐introduced plans calculated in the TPS. The gamma analysis with 2%L/2mm and 3%L/3mm tolerance criteria was also calculated by comparing the dose matrices.Results:For MLC shift errors, the TPS dose matrix comparison showed that the PTV‐D95 for the prostate plans reduced by a maximum (SD) of −8.4(3.3)% for the 5mm error. The 3DVH‐estimated D95 reduced from −0.5(2.0) for no‐error plans to −1.0(3.3)% for the 5mm MLC shift. Similarly for H&N plans the TPS‐calculated PTV‐D95 reduced by −5.1(3.8)%, with the 3DVH‐estimated D95 reducing from −1.5(2.2)% to −3.2(5.8)%. For gantry dependent MLC errors, the TPS D95 of prostate plans reduced to a maximum of −14.1(8.5)%, while the 3DVH‐estimated D95 reduced to 0.6(4.2)%. For H&N plans the TPS D95 reduced to −1.7(1.7)%, while the 3DVH‐estimated D95 reduced to −4.0(4.1)%. No major change in D95 was observed for gantry dependent dose errors for the TPS or 3DVH. In all error scenarios the gamma pass rate decreased as the magnitude of error increased.Conclusion:The gamma comparison of dose matrices was shown to detect all type of errors considered. The 3DVH‐estimated D95 agreed with the TPS more closely in H&N plans than prostate plans.This project was funded through a Cancer Council NSW Project Grant (RG14‐11)
SU‐F‐BRB‐10: A Statistical Voxel Based Normal Organ Dose Prediction Model for Coplanar and Non‐Coplanar Prostate Radiotherapy
Authors: Tran A , Yu V , Nguyen D , Woods K , Low D , Sheng K 
Published: June 2015

Purpose:Knowledge learned from previous plans can be used to guide future treatment planning. Existing knowledge‐based treatment planning methods study the correlation between organ geometry and dose volume histogram (DVH), which is a lossy representation of the complete dose distribution. A statistical voxel dose learning (SVDL) model was developed that includes the complete dose volume information. Its accuracy of predicting volumetric‐modulated arc therapy (VMAT) and non‐coplanar 4π radiotherapy was quantified. SVDL provided more isotropic dose gradients and may improve knowledge‐based planning.Methods:12 prostate SBRT patients originally treated using two full‐arc VMAT techniques were re‐planned with 4π using 20 intensity‐modulated non‐coplanar fields to a prescription dose of 40 Gy. The bladder and rectum voxels were binned based on their distances to the PTV. The dose distribution in each bin was resampled by convolving to a Gaussian kernel, resulting in 1000 data points in each bin that predicted the statistical dose information of a voxel with unknown dose in a new patient without triaging information that may be collectively important to a particular patient. We used this method to predict the DVHs, mean and max doses in a leave‐one‐out cross validation (LOOCV) test and compared its performance against lossy estimators including mean, median, mode, Poisson and Rayleigh of the voxelized dose distributions.Results:SVDL predicted the bladder and rectum doses more accurately than other estimators, giving mean percentile errors ranging from 13.35–19.46%, 4.81–19.47%, 22.49–28.69%, 23.35–30.5%, 21.05–53.93% for predicting mean, max dose, V20, V35, and V40 respectively, to OARs in both planning techniques. The prediction errors were generally lower for 4π than VMAT.Conclusion:By employing all dose volume information in the SVDL model, the OAR doses were more accurately predicted. 4π plans are better suited for knowledge‐based planning than the VMAT plans that are strongly biased in its dose gradient orientation.This project is supported by Varian Medical Systems.
SU‐F‐BRB‐12: A Novel Haar Wavelet Based Approach to Deliver Non‐Coplanar Intensity Modulated Radiotherapy Using Sparse Orthogonal Collimators
Authors: Nguyen D , Ruan D , O'Connor D , Low D , Boucher S , Sheng K 
Published: June 2015

Purpose:Existing efforts to replace complex multileaf collimator (MLC) by simple jaws for intensity modulated radiation therapy (IMRT) resulted in unacceptable compromise in plan quality and delivery efficiency. We introduce a novel fluence map segmentation method based on compressed sensing for plan delivery using a simplified sparse orthogonal collimator (SOC) on the 4π non‐coplanar radiotherapy platform.Methods:4π plans with varying prescription doses were first created by automatically selecting and optimizing 20 non‐coplanar beams for 2 GBM, 2 head & neck, and 2 lung patients. To create deliverable 4π plans using SOC, which are two pairs of orthogonal collimators with 1 to 4 leaves in each collimator bank, a Haar Fluence Optimization (HFO) method was used to regulate the number of Haar wavelet coefficients while maximizing the dose fidelity to the ideal prescription. The plans were directly stratified utilizing the optimized Haar wavelet rectangular basis. A matching number of deliverable segments were stratified for the MLC‐based plans.Results:Compared to the MLC‐based 4π plans, the SOC‐based 4π plans increased the average PTV dose homogeneity from 0.811 to 0.913. PTV D98 and D99 were improved by 3.53% and 5.60% of the corresponding prescription doses. The average mean and maximal OAR doses slightly increased by 0.57% and 2.57% of the prescription doses. The average number of segments ranged between 5 and 30 per beam. The collimator travel time to create the segments decreased with increasing leaf numbers in the SOC. The two and four leaf designs were 1.71 and 1.93 times more efficient, on average, than the single leaf design.Conclusion:The innovative dose domain optimization based on compressed sensing enables uncompromised 4π non‐coplanar IMRT dose delivery using simple rectangular segments that are deliverable using a sparse orthogonal collimator, which only requires 8 to 16 leaves yet is unlimited in modulation resolution.This work is supported in part by Varian Medical Systems, Inc. and NIH R43 CA18339.
SU‐F‐BRB‐13: Correlation of Improved Target and Organ‐At‐Risk Dosimetric Quantities and Clinical Outcomes for Helical Tomotherapy Treated Mesothelioma
Authors: Qi S , Kishan A , Alexander S , Lee P , Selch M , Kupelian P , Steiberg M , Low D 
Published: June 2015

Purpose:We have observed improved local control probability (LCP) for adjuvant mesothelioma radiotherapy following pleurectomy/decortication using Tomotherapy compared to the conventional 3D technique (p<0.05). This work assesses the correlation between the improved clinical outcomes against dosimetry quantities.Methods:Thirty‐eight mesothelioma cases consecutively treated at our clinic were retrospectively analyzed. Sixteen patients were treated using 3D technique planned on the Eclipse for c‐arm accelerators prior to 7/2012; the other 22 cases were treated on Tomotherapy using helical IMRT after 7/2012. Typical 3D plans consisting of 15 MV AP/PA photon fields prescribed to 10 cm depth followed by matching electron fields with energy ranging from 8–16 MeV. Tomotherapy plans were designed using 2.5cm jaw, 0.287 pitch with directional blocking of the contralateral lung. The same prescription of 45 Gy (1.8GyX25) was used for both techniques. The dosimetry metrics for the critical structures: ipsilateral‐/contralateral‐lung, heart, cord, esophagus, etc were compared between two techniques.Results:Superior LCP is closely associated with improved target coverage. Tomotherapy plans yielded dramatically better target coverage and less dose heterogeneity despite of more advanced/larger disease. The averaged PTV volumes were 2287.3±569.9 (Tomotherapy) vs. 1904.8±312.3cc (3D); V100s were: 91.1±4.0 (%) vs. 47.8±12.7 (%) with heterogeneity indices of 1.20±0.1 vs.1.37±0.38 and for the Tomotherapy and 3D plans, respectively. Compared to the 3D technique, we observed significant lower maximum cord doses (p<0.001), lower mean esophagus doses (p<0.002), and lower heart mean doses when tumor was left‐sided (p=0.002). For ipsilateral‐/contralateral‐lungs, however, the mean doses and V20, V5 of Tomotherapy plans were significantly higher than the 3D plans (p<0.01) regardless which sides of lung were treated. However, rates of radiation pneumonitis were no different.Conclusion:Tomotherapy achieved great improvement of plan quality including target coverage, resulting in significantly better local control over the traditional 3D technique for adjuvant radiotherapy for mesothelioma.