bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐369: Evaluating Intensity Modulated Proton Therapy Relative to Passive Scattering Proton Therapy for Increased Vertebral Column Sparing in CSI of Pediatric Patients
Authors: Seco J , Giantsoudi D , Eaton BR , Adams JA , Paganetti H , MacDonald S 
Published: June 2015

Purpose:To investigate the trade‐off between vertebral column sparing and thecal‐sac target coverage in craniospinal irradiation (CSI) of pediatric patients treated with passive‐scattering (PS) and intensity modulated (IMPT) proton therapy.Methods:We selected 2 pediatric patients treated with PS CSI for medulloblastoma. Spinal irradiation was re‐planned with IMPT. For all cases, we assumed prescription dose of 23.4 Gy(RBE), with the spinal canal receiving at least 95% of 23.4 Gy(RBE). PS planning was performed using the commercial system XiO. IMPT planning was done using the Astroid planning system. Beam arrangements consisted of (a) PS posterior‐anterior (PA) field, PS‐PA, (b) IMPT PA field, IMPT‐PA, and (c) two posterior oblique IMPT fields, IMPT2 (‐35°, 35°). Dose distributions were re‐calculated using TOPAS Monte Carlo, along with LET distributions, to investigate LET variations within the target and vertebra anatomy. Variable RBE‐weighed dose distributions were also calculated based on a dose and LET‐dependent biophysical model. Dosimetric data were compared among the plans for the target volume, spinal cord and adjacent critical organs (thecal‐sac and cauda equina).Results:IMPT2 resulted in better sparing of the posterior vertebral column (entrance region posterior to thecal‐sac), where planned dose was approximately 6–8Gy(RBE). For IMPT‐PA and PS‐PA the MC‐calculated dose to the posterior vertebral column was, on average, 20Gy and 18Gy respectively. For IMPT2 higher mean‐LET (5keV/µm/(g/cm3)) values were observed in anterior vertebral column (beyond the thecal‐sac) relative to IMPT‐PA and PS‐PA, where mean‐LET was 3.5keV/µm/(g/cm3) and 2.5keV/µm/(g/cm3) respectively. The higher LET region observed for both IMPT plans was in the distal end of treatment fields, where dose delivered was less 5Gy(RBE).Conclusion:The two‐oblique proton beams IMPT2 best spared the spinal column, while reducing the dose to the posterior spinal column from 18–20 to 6–8 Gy(RBE). The best LET distribution was obtained with the PS‐PA fields.
SU‐E‐T‐377: Evaluation of a Novel Transmission Detector as a Reference Chamber for Use in Beam Measurements
Authors: Epstein D , Shekel E , Levin D 
Published: June 2015

Purpose:To evaluate a new transmission chamber for use as a reference chamber in measurements of beam dataMethods:We assessed the performance of a new transmission detector, the Stealth Chamber, manufactured by IBA (IBA Dosimetry). The chamber has an active volume of 249 cm3, with an attenuation equivalent of <0.5mm Al. We mounted the chamber to a TrueBeam linac (Varian Medical Systems, Palo Alto, CA) such that the active area is perpendicular to the beam direction. We performed PDD and profile measurements on field sizes from 1×1 cm2 to 10×10 cm2, as well as for a 4 mm cone. The field detector was either a CC‐13 chamber (IBA Dosimetry) with an active volume of 0.13 cm3 or an Edge Detector (Sun Nuclear, Melbourne, FL) with an active volume of 0.019 cm3. For comparison we repeated all measurements using a CC‐13 or CC‐01 (active volume 0.01 cm3 ) chamber as reference detectors (IBA Dosimetry).All scans were acquired using a Blue Phantom2 (IBA Dosimetry) and IBA OmniPro‐Accept v7.4.24 software.Results:All measurements with the Stealth Chamber were identical to those with ion reference chambers. For both regular and filter free 6MV beams there was agreement in PDDs and profiles, including the penumbra region, for all field sizes. This was true for the 4mm cone measurement, as well. The deviation between the Stealth and ion chamber measurements was on average 0.3%.Conclusion:The Stealth Chamber gives identical beam data as a conventional ion chamber for all field sizes. The advantage of the Stealth chamber over ion chambers is its efficiency. Once mounted, there is no need to reposition the chamber with varying field sizes. This translates into a huge savings in measurement time, as well as a reduction in potential errors due to reference chamber mispositioning.
SU‐E‐T‐395: Evaluation of Multiple Brain Metastases Stereotactic Treatment Planning in Cyberknife Versus Linac
Authors: Vikraman S , Manigandan D , Rajesh Thiyagarajan , Karrthick Kp , Sambasivaselli R , Senniandavar V , Ramu M , Maragathaveni S , Dhivya N , Muthukumaran M , Tejinder K 
Published: June 2015

Purpose:The purpose of this study was to evaluate multiple brain metastases stereotactic treatment planning of Cyberknife versus linac using dose volume based indices.Methods:Fifteen multiple brain metastases patients were taken for this study from Cyberknife Multiplan TPSv4.6.0. All these patients underwent stereotactic treatment in Cyberknife. For each patient VMAT stereotactic treatment plan was generated in MONACO TPSv5.0 using Elekta beam modulator MLC and matched the delivered plan. A median dose of 8.5Gy(range 7–12Gy) per fraction was prescribed. Tumor volume was in the range of 0.06–4.33cc. Treatment plan quality was critically evaluated by comparing DVH indices such as D98, D95, CI, and HI for target volumes. Maximum point doses and volume doses were evaluated for critical organs.Results:For each case, target coverage of D98 was achieved with 100% prescription dose with SD of 0.29% and 0.41% in Linac and Cyberknife respectively. The average conformity index(CI) of 1.26±0.0796 SD for Cyberknife and 1.92±0.60SD for linac were observed. Better homogeneity Index (HI) of 1.17±0.09SD was observed in linac as compared to Cyberknife HI of 1.24±0.05SD.All the critical organ doses were well within tolerance limit in both linac and Cyberknife plans. There is no significant difference of maximum point doses for brainstem and optic chiasm. Treatment time and number of monitor units are more in Cyberknife compared to linac. The average volume receiving 12Gy in whole brain was 6% and 12% for Cyberknife and linac respectively. 1000cc of whole brain received 60% lesser dose in Linac compared to Cyberknife in all cases.Conclusion:The study shows that dosimetrically comparable plans are achievable Cyberknife and Linac. However, a better conformity, target coverage, lesser OAR dose is achieved with Cyberknife due to greater degrees of freedom with robotic gantry and smaller collimator for multiple targets.
SU‐E‐T‐401: Evaluation of TG‐43 Dose Calculation Accuracy for SAVI‐Based Accelerated Partial Breast Irradiation (APBI) Via Monte Carlo Simulations
Authors: Xu Y , Tian Z , Scanderbeg D , Zhang M , Yashar C , Jiang S , Jia X 
Published: June 2015

Purpose:The current standard TG‐43 dose calculation method for SAVI‐based Accelerated Partial Breast Irradiation (APBI) assumes an ideal geometry of infinite homogeneous water. However, in SAVI treatments, the air cavity inside the device and the short source‐to‐skin distance raise concerns about the dose accuracy of the TG‐43 method. This study is to evaluate TG‐43 dose calculation accuracy in SAVI treatments using Monte Carlo (MC) simulations.Methods:We recalculated the dose distributions of 15 APBI patients treated with SAVI devices, including five cases with a size of 6–1, five with 8−1 and five with 10−1, using our in‐house developed fast MC dose package for HDR brachytherapy (gBMC). A phase‐space file was used to model the Ir‐192 HDR source. For each case, the patient CT was converted into a voxelized phantom and the dwell positions and times were extracted from treatment plans for MC dose calculations. Clinically relevant dosimetric parameters of the recalculated dose were compared to those computed via the TG‐43 approach.Results:A systematic overestimation of doses was found for the 15 cases in TG‐43 results, with D90, V150, and V200 for PTV_eval 2.8±1.8%, 2.0±2.2%, and 1.8±3.5% higher than MC results. TG‐43 also overestimated the dose to skin with the maximum dose 4.4±8.4% higher on average. The relatively large standard deviation seen in the difference of maximum skin dose is partially ascribed to the statistical uncertainty of MC simulations when computing the maximum dose. It took gBMC ∼1 minute to compute dose for a SAVI plan.Conclusion:The high efficiency of our gBMC package facilitated the studies with a relatively large number of cases. An overestimation of TG‐43 doses was found when using this MC package to recompute doses in SAVI cases. Clinical utilization of TG‐43 dose calculation method in this scenario should be aware of this fact.
SU‐E‐T‐410: Evaluation of Treatment Modalities for Stereotactic Lung Radiation Therapy: A Phantom Study
Authors: Mohatt D , Malhotra H 
Published: June 2015

Purpose:To evaluate and verify the accuracy of alternative treatment modalities for stereotactic lung therapy with end‐to‐end testing. We compared three dimensional conformal therapy (3DCRT), dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment using 6 MV, 6 MV flattening filter free (FFF) and 10 MV FFF photons.Methods:A QUASAR respiratory motion phantom was utilized with custom ion chamber and gafchromatic EBT2 film inserts. The phantom contained a low density lung medium with a cylindrical polystyrene tumor (35 cc). Pseudo representative structures for various organs at risk (OAR) were created. All treatment plans were created using Eclipse ver. 11 using the same image and structure sets, and delivered via Varian TrueBeam STx linear accelerator equipped with high definition MLC. Evaluation of plan quality followed ROTG 0813 criterion for conformity index (CI100%), high dose spillage, D2cm, and R50%.Results:All treatment plans met the OAR dose constraints per protocol and could be delivered without any beam hold offs or other interlocks and hence were deemed clinically safe. For equivalent beam energies, target conformity was improved for all modalities when switching to FFF mode. Treatment efficiency increased for VMAT FFF by a factor of 3–4 over IMRT, and up to factor of 7 when compared to 3DCRT. Pass rates were > 97% for all treatment using gamma criteria of 3%, 3mm. Absolute dose at iso‐center was verified with ion chamber, and found to be within 2% of the treatment planning system.Conclusion:The higher dose rate associated with FFF not only reduces delivery times, but in most cases enhances plan quality. The one modality with succeeding best results for all RTOG criterions was VMAT 6 MV FFF. This end‐to‐end testing provides necessary confidence in the entire dose delivery chain for lung SBRT patients.
SU‐E‐T‐421: Failure Mode and Effects Analysis (FMEA) of Xoft Electronic Brachytherapy for the Treatment of Superficial Skin Cancers
Authors: Hoisak J , Manger R , Dragojevic I 
Published: June 2015

Purpose:To perform a failure mode and effects analysis (FMEA) of the process for treating superficial skin cancers with the Xoft Axxent electronic brachytherapy (eBx) system, given the recent introduction of expanded quality control (QC) initiatives at our institution.Methods:A process map was developed listing all steps in superficial treatments with Xoft eBx, from the initial patient consult to the completion of the treatment course. The process map guided the FMEA to identify the failure modes for each step in the treatment workflow and assign Risk Priority Numbers (RPN), calculated as the product of the failure mode's probability of occurrence (O), severity (S) and lack of detectability (D). FMEA was done with and without the inclusion of recent QC initiatives such as increased staffing, physics oversight, standardized source calibration, treatment planning and documentation. The failure modes with the highest RPNs were identified and contrasted before and after introduction of the QC initiatives.Results:Based on the FMEA, the failure modes with the highest RPN were related to source calibration, treatment planning, and patient setup/treatment delivery (Fig. 1). The introduction of additional physics oversight, standardized planning and safety initiatives such as checklists and time‐outs reduced the RPNs of these failure modes. High‐risk failure modes that could be mitigated with improved hardware and software interlocks were identified.Conclusion:The FMEA analysis identified the steps in the treatment process presenting the highest risk. The introduction of enhanced QC initiatives mitigated the risk of some of these failure modes by decreasing their probability of occurrence and increasing their detectability. This analysis demonstrates the importance of well‐designed QC policies, procedures and oversight in a Xoft eBx programme for treatment of superficial skin cancers. Unresolved high risk failure modes highlight the need for non‐procedural quality initiatives such as improved planning software and more robust hardware interlock systems.
SU‐E‐T‐425: Feasibility of Establishing a National Postal Dosimetry System Using EBT3 Gafchromic Film
Authors: Abdel‐Rahman W , Mohammed I , Bamajboor S 
Published: June 2015

Purpose:To evaluate the performance of a postal dosimeter consisting of EBT3 films and a miniature Lucite phantom to be used for photon beams output audits for mega‐voltage photon beams across the Saudi Arabia.Methods:Two batches of EBT3 films were calibrated in 5 mega‐voltage photon beams with energies ranging between 6 MV and 18 MV in the dose range between 0 to 4 Gy. A 4×4×20 cm3 lucite phantom was constructed to be used as an irradiation phantom. The lucite irradiation phantom consists of two parts and allows for embedding a 2.5×2.0 cm2 EBT3 film at 8.9 cm depth. Factors that convert the dose measured in the lucite irradiation phantom at 8.9 cm depth to the dose at 10 cm depth in water for 10×10 cm2 field for different photon energies were calculated using the dosxyznrc/EGSnrcMP user code. The performance of the proposed postal dosimeter was tested in 17 different photon beams across 4 radiotherapy centres in Saudi Arabia. The outputs of the 17 beams are monitored by either the International Atomic Energy Agency or by the Radiological Physics Centre.Results:For the 17 photon beams, the average of the ratios of measured to stated outputs was 1.01 ± 0.02 and with a maximum ratio of 1.05.Conclusion:The results of our work indicate that the proposed postal dosimetry system can be used for national auditing of outputs for mega‐voltage photon beams. The service can be offered to other national radiotherapy centres or to a be used for credentialing of centres participating in national trials.
SU‐E‐T‐426: Feasibility of Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancer Using Volumetric Modulated Arc Therapy (VMAT) with Active Breathing Control (ABC)
Authors: Zhang Y , Jackson J , Davies G , Herman J , Forbang R Teboh 
Published: June 2015

Purpose:SBRT shows excellent tumor control and toxicity rates for patients with locally advanced pancreatic cancer (PCA). Herein, we evaluate the feasibility of using VMAT with ABC for PCA SBRT.Methods:Nine PCA patients previously treated via SBRT utilizing 11‐beam step‐and‐shoot IMRT technique in our center were retrospectively identified, among whom eight patients received 3300cGy in 5 fractions while one received 3000cGy in 5 fractions. A VMAT plan was generated on each patient's planning CT in Pinnacle v9.8 on Elekta Synergy following the same PCA SBRT clinical protocol. Three partial arcs (182°–300°, 300°‐60°, and 60°‐180°) with 2°/4° control‐point spacing were used. The dosimetric difference between the VMAT and the original IMRT plans was analyzed. IMRT QA was performed for the VMAT plans using MapCheck2 in MapPHAN and the total delivery time was recorded. To mimic the treatment situation with ABC, where patients hold their breath for 20–30 seconds, the delivery was intentionally interrupted every 20–30 seconds. For each plan, the QA was performed with and without beam interruption. Gamma analysis (2%/2mm) was used to compare the planned and measured doses.Results:All VMAT plans with 2mm dose grid passed the clinic protocol with similar PTV coverage and OARs sparing, where PTV V_RxDose was 92.7±2.1% (VMAT) vs. 92.1±2.6% (IMRT), and proximal stomach V15Gy was 3.60±2.69 cc (VMAT) vs. 4.80±3.13 cc (IMRT). The mean total MU and delivery time of the VMAT plans were 2453.8±531.1 MU and 282.1±56.0 seconds. The gamma passing rates of absolute dose were 94.9±3.4% and 94.5±4.0% for delivery without and with interruption respectively, suggesting the dosimetry of VMAT delivery with ABC for SBRT won't be compromised.Conclusion:This study suggests that PCA SBRT using VMAT with ABC is a feasible technique without compromising plan dosimetry. The combination of VMAT with ABC will potentially reduce the SBRT treatment time.
SU‐E‐T‐431: Feasiblity of Using CT Scout Images for 2D LDR Brachytherpay Planning
Authors: Ha J , Weaver R 
Published: June 2015

Purpose:i) To show the feasibility of using CT scout images for 2D low‐dose rate brachytherapy planning with BrachyVision (version 10.4); ii) to show their advantages and disadvantages over DRRs.Methods:A phantom was constructed to house a Fletcher‐Suite applicator. The phantom is made of Styrofoam with metal BBs positioned at well‐defined separations. These markers are used to assess the image distortion in the scout images. Unlike DRRs, scout images are distorted only in the direction normal to the couch direction; therefore, they needed to be scaled unidirectionally prior to importing into BrachyVision. In addition to confirming the scaling is performed correctly by measuring distances between well‐positioned BB, we also compare a LDR plan using scout images to a 3D CT‐based plan.Results:There is no distortion of the image along the couch direction due to the collimation of the CT scanner. The distortion in the transverse plane can be corrected by multiplying by the ratio of distances between source‐to‐isocenter and source‐to‐detector. The results show the distance separations between BBs as measured in scout images and by a caliber are within a few millimeters. Dosimetrically, the difference between the dose rates to points A and B based on scout images and on 3D CT are less than a few percents. The accuracy can be improved by correcting for the distortion on the transverse plane.Conclusion:It is possible to use CT scout images for 2D planning in BrachyVision. This is an advantage because scout images have no metal artifacts often present in CT images or DRRs. Another advantage is the lack of distortion in the couch direction. One major disadvantage is that the image distortion due to beam divergence can be large. This is due to the inherent short distance between source‐to‐isocenter and source‐to‐detector on a CT scanner.
SU‐E‐T‐432: Field Size Influence On the Electron and Photon Spectra Within Small MV Field Detectors
Authors: Benmakhlouf H , Andreo P 
Published: June 2015

Purpose:To investigate the influence of photon field size on the electron and photon fluence spectra in the active volume of small field detectors.Methods:The PENELOPE MC system based usercode PenEasy was used to calculate the material influence on the spectra by scoring the differential fluence in inserts of silicon, carbon, phosphorus and aluminium having 3 mm diameter and height. The spectra were then calculated inside the active volume of eleven detectors (ion chambers and solid‐state detectors) whose geometry was simulated with great detail. The inserts/detectors were placed at 10 cm depth in a 30 cm × 30 cm × 30 cm water phantom and irradiated with 2.5 MeV photons and Varian Clinac 6 MV beams of small, medium and large size.Results:For all configurations, photon spectra in the scoring volume were similar to that in a small water volume except for additional characteristic x‐ray peaks resulting from the material itself and from the materials surrounding the detectors (i.e. high‐Z shielding the silicon). Electron fluence calculated in the inserts were up to 60% larger than in water; the difference increased with material density and decreasing field size. MC‐calculated doses were compared to analytically determined collision kerma and restricted cema (cut‐off=15keV). For the inserts, with large and medium fields K_col agreed with MC‐dose, but K_col overestimated the dose for small fields due to lack of lateral CPE. For the detectors, up to 15% differences between K_col and the MC‐dose were found. For all configurations the C‐delta and MC‐dose agreed within ±2%.Conclusion:The most relevant findings were that shielding affects substantially the photon spectra and material conditions the electron spectra, their field size dependence varying with the geometry configuration. These affect the values of factors entering into relative dosimetry.
SU‐E‐T‐441: Gamma Passing Rates for IMRT QA and VMAT QA
Authors: Kremmel E , Giaddui T , Keller J , Fu M , Peng C , Doyle L , Yu Y , Harrison A 
Published: June 2015

Purpose:This study compares gamma passing rates for a cohort of similar intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) quality assurance (QA) plans to determine the equivalence of the patient specific QA plan delivery. The passing criterion is 90% gamma index with 3% dose difference (DD), 3mm distance‐to‐agreement (DTA) and a dose threshold of 10%.Methods:Gamma passing results of previously treated IMRT QA plans, delivered to Sun Nuclear MapCheck phantom, and VMAT QA plans, delivered to ScandiDos Delta4 phantom, are organized by anatomical site and treatment machine. Both Varian and Elekta machines are included. Pairs of IMRT and VMAT plans are matched based on site, machine, and PTV volume to ensure similar plan cohorts. A two‐tailed t‐test analysis of the data with an alpha of 0.05 determines if there exists a statistically significant difference. Power was calculated to detect a difference of 4%; all data sets were strong with above a 0.8 power.Results:The first data set consisting of 20 matched pairs of prostate plans was statistically insignificant (p‐value=0.90, Power=0.99). The 14 matched pairs set of head and neck plans has a statistically significant Result (p‐value=0.028, Power=0.88). The head and neck IMRT gamma indexes have a mean of 93.1% and range of 82%‐100% while the VMAT gamma indexes have a mean of 96.7% and range of 92%‐100%. The two combined data sets of matched plans had a statistically insignificant Result (p‐value=0.073, Power=0.99).Conclusion:Overall, IMRT and VMAT have equivalent passing rates when comparing the gamma analysis using a passing criterion of 3% DD and 3mm DTA. When separated by site, prostate IMRT and VMAT plans have equivalent passing rates while head and neck plans have a statistically significant variation of passing rates. The passing rates for the two modalities are independent of delivery machine for matched PTV target volumes.