bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐189: Dosimetric Comparison of Spot‐Scanning Proton Therapy Techniques for Liver Tumors Close to the Skin Surface
Authors: Takao S , Matsuura T , Matsuzaki Y , Fujii Y , Fujii T , Katoh N , Shimizu S , Umegaki K , Shirato H 
Published: July 2016

Purpose:Spot‐scanning technique has been utilized to achieve conformal dose distribution to large and complicated tumors. This technique generally does not require patient‐specific devices such as aperture and compensator. The commercially available spot‐scanning proton therapy (SSPT) systems, however, cannot deliver proton beams to the region shallower than 4 g/cm2. Therefore some range compensation device is required to treat superficial tumors with SSPT. This study shows dosimetric comparison of the following treatment techniques: (i) with a tabletop bolus, (ii) with a nozzle‐mounted applicator, and (iii) without any devices and using intensity‐modulated proton therapy (IMPT) technique.Methods:The applicator composed of a combination of a mini‐ridge filter and a range shifter has been manufactured by Hitachi, Ltd., and the tabletop bolus was made by .decimal, Inc. Both devices have been clinically implemented in our facility. Three patients with liver tumors close to the skin surface were examined in this study. Each treatment plan was optimized so that the prescription dose of 76 Gy(RBE) or 66 Gy(RBE) would be delivered to 99% of the clinical target volume in 20 fractions. Three beams were used for tabletop bolus plan and IMPT plan, whereas two beams were used in the applicator plan because the gantry angle available was limited due to potential collision to patient and couch. The normal liver, colon, and skin were considered as organs at risk (OARs).Results:The target heterogeneity index (HI = D5/D95) was 1.03 on average in each planning technique. The mean dose to the normal liver was considerably less than 20 Gy(RBE) in all cases. The dose to the skin could be reduced by 20 Gy(RBE) on average in the IMPT plan compared to the applicator plan.Conclusion:It has been confirmed that all treatment techniques met the dosimetric criteria for the OARs and could be implemented clinically.
SU‐F‐T‐194: Analyzing the Effect of Range Shifter Air Gap On TPS Dose Modeling Accuracy in Superficial PBS Proton Therapy
Authors: Shirey R , Wu H 
Published: July 2016

Purpose:Treatment planning systems (TPS) may not accurately model superficial dose distributions of range shifted proton pencil beam scanning (PBS) treatments. Numerous patient‐specific QA tests performed on superficially treated PBS plans have shown a consistent overestimate of dose by the TPS. This study quantifies variations between TPS planned dose and measured dose as a function of range shifter air gap and treatment depths up to 5 cm.Methods:PBS treatment plans were created in the TPS to uniformly irradiate a volume of solid water. One plan was created for each range shifter position analyzed, and all plans utilized identical dose optimization parameters. Each optimized plan was analyzed in the TPS to determine the planned dose at varying depths. A PBS proton therapy system with a 3.5 cm lucite range shifter delivered the treatment plans, and a parallel plate chamber embedded in RW3 solid water measured dose at shallow depths for each air gap. Differences between measured and planned doses were plotted and analyzed.Results:The data show that the TPS more accurately models superficial dose as the air gap between the range shifter and patient surface decreases. Air gaps less than 10 cm have an average dose difference of only 1.6%, whereas air gaps between 10 and 20 cm differ by 3.0% and gaps greater than 20 cm differ by 4.4%.Conclusion:This study has shown that the TPS is unable to accurately model superficial dose with a large range shifter air gap. Dose differences greater than 3% will likely cause QA failure, as many institutions analyze patient QA with a 3%/3mm gamma analysis. For superficial PBS therapy, range shifter positions should be chosen to keep the air gap less then 10 cm when patient setup and gantry geometry allow.
SU‐F‐T‐201: Acceleration of Dose Optimization Process Using Dual‐Loop Optimization Technique for Spot Scanning Proton Therapy
Authors: Hirayama S , Fujimoto R 
Published: July 2016

Purpose:The purpose was to demonstrate a developed acceleration technique of dose optimization and to investigate its applicability to the optimization process in a treatment planning system (TPS) for proton therapy.Methods:In the developed technique, the dose matrix is divided into two parts, main and halo, based on beam sizes. The boundary of the two parts is varied depending on the beam energy and water equivalent depth by utilizing the beam size as a singular threshold parameter. The optimization is executed with two levels of iterations. In the inner loop, doses from the main part are updated, whereas doses from the halo part remain constant. In the outer loop, the doses from the halo part are recalculated. We implemented this technique to the optimization process in the TPS and investigated the dependence on the target volume of the speedup effect and applicability to the worst‐case optimization (WCO) in benchmarks.Results:We created irradiation plans for various cubic targets and measured the optimization time varying the target volume. The speedup effect was improved as the target volume increased, and the calculation speed increased by a factor of six for a 1000 cm3 target. An IMPT plan for the RTOG benchmark phantom was created in consideration of ±3.5% range uncertainties using the WCO. Beams were irradiated at 0, 45, and 315 degrees. The target's prescribed dose and OAR's Dmax were set to 3 Gy and 1.5 Gy, respectively. Using the developed technique, the calculation speed increased by a factor of 1.5. Meanwhile, no significant difference in the calculated DVHs was found before and after incorporating the technique into the WCO.Conclusion:The developed technique could be adapted to the TPS's optimization. The technique was effective particularly for large target cases.
SU‐F‐T‐206: Proton Treatment Techniques for Posterior Fossa Tumors: Consequences for LET and Dose/Volume Parameters for the Brainstem and Organs at Risk
Authors: Giantsoudi D , Adams J , MacDonald S , Paganetti H 
Published: July 2016

Purpose:In proton radiation therapy of posterior fossa tumors, to spare other sensitive structures, the preferred beam geometry results in placing the treatment field distal edge within or just beyond the brainstem, including in at least partially in the treatment volume. Concerns for brainstem toxicity are increased and a controversy exists as to weather the beam's distal edge should be placed within the brainstem or beyond it, to avoid elevated linear energy transfer (LET) and relative biological effectiveness (RBE) within the brainstem. The dosimetric efficacy of these techniques was examined, accounting for LET‐ and dose‐dependent variable RBE distributions.Methods:Three treatment planning techniques were applied in six ependymoma cases: (a) three‐field dose‐sparing, with beams’ distal edge within the brainstem; (b) three‐field LET‐sparing, using same beam directions as (a) but extended field ranges beyond the brainstem; (c) two‐posterior‐oblique LET‐sparing, with extended ranges as (b). Monte Carlo calculated dose, LET and RBE‐weighted dose distributions were compared.Results:Lower LET values in the brainstem were accompanied by higher median dose: 53.7 Gy[RBE] and 54.3 Gy[RBE] for techniques (b) and (c) versus 52.1 Gy[RBE] for (a). Accounting for variable RBE, a 15% increase of the brainstem volume receiving at least 60 Gy[RBE] was observed for technique (c) versus (a). Maximum variable‐RBE‐weighted brainstem dose was comparable for all techniques.Conclusion:Extending the treatment beam range beyond the brainstem, significantly increased its volume receiving high dose radiation, even when accounting for the decreased LET values. The dosimetric benefits of techniques limiting the brainstem dose may outweigh the impact of LET reduction achieved through this technique, especially since clinical consequences of increased LET at the end of range have not been proven yet.
SU‐F‐T‐211: Evaluation of a Dual Focusing Magnet System for the Treatment of Small Proton Targets
Authors: Nguyen TT , McAuley GA , Heczko S , Slater J , Wroe A 
Published: July 2016

Purpose:To investigate magnetic focusing for small volume proton targets using a doublet combination of quadrupole rare earth permanent magnet Halbach cylinder assembliesMethods:Monte Carlo computer simulations were performed using the Geant4 toolkit to compare dose depositions of proton beams transported through two focusing magnets or in their absence. Proton beams with energies of 127 MeV and initial diameters of 5, 8 and 10 mm were delivered through two identical focusing magnets similar to those currently in experimental use at Loma Linda University Medical Center. Analogous experiments used optimized configurations based on the simulation results. Dose was measured by a diode detector and Gafchromic EBT3 film and compared to simulation data. Based on results from the experimental data, an additional set of simulations was performed with an initial beam diameter of 18 mm and a two differing length magnets (40mm & 68mm).Results:Experimental data matched well with Monte Carlo simulations. However, under conditions necessary to produce circular beam spots at target depth, magnetically focused beams using two identical 40 mm length magnets did not meet all of our performance criteria of circular beam spots, improved peak to entrance (P/E) dose ratios and dose delivery efficiencies. The simulations using the longer 68 mm 2nd magnet yielded better results with 34% better P/E dose ratio and 20–50% better dose delivery efficiencies when compared to unfocused 10 mm beams.Conclusion:While magnetic focusing using two magnets with identical focusing power did not yield desired results, ongoing Monte Carlo simulations suggest that increasing the length of the 2nd magnet to 68 mm could improve P/E dose ratios and dose efficiencies. Future work includes additional experimental validation of the longer 2nd magnet setup as well as experiments with triplet magnet systems.This project was sponsored with funding from the Department of Defense (DOD# W81XWH‐BAA‐10‐1).
SU‐F‐T‐215: An Investigation Of Multi‐Scanner CT Hounsfield Unit Calibration for Pencil Beam Scanning Proton Therapy Using 3D Gamma Analysis
Authors: Zhang J , Li X , Liu G , Liu Q , Liang J , Ding X 
Published: July 2016

Purpose:We compare and investigate the dosimetric impacts on pencil beam scanning (PBS) proton treatment plans generated with CT calibration curves from four different CT scanners and one averaged ‘global’ CT calibration curve.Methods:The four CT scanners are located at three different hospital locations within the same health system. CT density calibration curves were collected from these scanners using the same CT calibration phantom and acquisition parameters. Mass density to HU value tables were then commissioned in a commercial treatment planning system. Five disease sites were chosen for dosimetric comparisons at brain, lung, head and neck, adrenal, and prostate. Three types of PBS plans were generated at each treatment site using SFUD, IMPT, and robustness optimized IMPT techniques. 3D dose differences were investigated using 3D Gamma analysis.Results:The CT calibration curves for all four scanners display very similar shapes. Large HU differences were observed at both the high HU and low HU regions of the curves. Large dose differences were generally observed at the distal edges of the beams and they are beam angle dependent. Out of the five treatment sites, lung plans exhibits the most overall range uncertainties and prostate plans have the greatest dose discrepancy. There are no significant differences between the SFUD, IMPT, and the RO‐IMPT methods. 3D gamma analysis with 3%, 3 mm criteria showed all plans with greater than 95% passing rate. Two of the scanners with close HU values have negligible dose difference except for lung.Conclusion:Our study shows that there are more than 5% dosimetric differences between different CT calibration curves. PBS treatment plans generated with SFUD, IMPT, and the robustness optimized IMPT has similar sensitivity to the CT density uncertainty. More patient data and tighter gamma criteria based on structure location and size will be used for further investigation.
SU‐F‐T‐221: An Assessment of the Potential for Improved Local Control of Skull‐ Base Chordomas Via Reduction of the Proton Beam Range Uncertainty
Authors: Muller L , Soldner A , Kirk M , Fager M , Solberg T , Robert L , Dolney D 
Published: July 2016

Purpose:The beam range uncertainty presents a special challenge for proton therapy. Novel technologies currently under development offer strategies to reduce the range uncertainty [1,2]. This work quantifies the potential advantages that could be realized by such a reduction for dosimetrically challenging chordomas at the base of skull. Therapeutic improvement was assessed by evaluating tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP).Methods:Treatment plans were made for a modulated‐scanned proton delivery technique using the Eclipse treatment planning system. The prescription dose was 7920 cGy to the CTV. Three different range uncertainty scenarios were considered: 5 mm (3.5% of the beam range + 1 mm, representing current clinical practice, “Curr”), 2 mm (1.3%), and 1 mm (0.7%). For each of 4 patients, 3 different PTVs were defined via uniform expansion of the CTV by the value of the range uncertainty. Tumor control probability (TCP) and normal tissue complication probabilities (NTCPs) for organs‐at‐risk (OARs) were calculated using the Lyman‐Kutcher‐Burman[3] formalism and published model parameters [ref Terahara[4], quantec S10, Burman Red Journal v21 pp 123]. Our plan optimization strategy was to achieve PTV close to prescription while maintaining OAR NTCP values at or better than the Curr plan.Results:The average TCP values for the 5, 2, and 1 mm range uncertainty scenarios are 51%, 55% and 65%. The improvement in TCP for patients was between 4 and 30%, depending primarily on the proximity of the GTV to OAR. The average NTCPs for the brainstem and cord were about 4% and 1%, respectively, for all target margins.Conclusion:For base of skull chordomas, reduced target margins can substantially increase the TCP without increasing the NTCP. This work demonstrates the potential significance of a reduction in the range uncertainty for proton beams.
SU‐F‐T‐225: Is It Time to Have Pre‐Configured Therapeutic Beams Available in Commercial Treatment Planning Systems?
Authors: Ding G 
Published: July 2016

Purpose:Commissioning radiation beams requires considerable effort to obtain the beam data for beam configuration in a commercial treatment planning system. With the advances in technology, the manufacturer of accelerators now has the ability to adjust radiation beam parameters to meet pre‐determined specifications with high precision. This study aims to illustrate the feasibility of making pre‐configured radiation beams available in commercial treatment planning systems.Methods:In recent years, Varian has made a set of measured beam data from the TrueBeam accelerator available to users. Although the beam data are provided as “suggestive data” without warranty, the commissioned data measured by users have been shown to be in excellent agreement with the data set provided when the beams from the installed Linacs were adjusted to meet the beam specifications. An unofficial survey among Varian Linac TrueBeam users shows that the suggestive data set has been used with validation by users in some clinics. This indicates that radiation beams from a specified Linac can be standardized and pre‐configured in a treatment planning system.Results:Two newly installed Varian TrueBeam accelerators at two different centers were examined in which one set of commissioned beam data was obtained from measurements performed by an independent physics consulting company and the other was measured by local physicists in the department. All beams from both accelerators were tuned to meet the manufacturer's specifications. Discrepancies of less than 1% were found between the commissioned beam data from both accelerators and the suggestive data set provided by Varian.Conclusion:It may be feasible that radiation beams can be pre‐configured in commercial treatment planning systems. The radiation beam users will perform the beam validation and end‐to‐end tests instead of configuring beams. This framework can increase both the efficiency and the accuracy in commercial radiation treatment planning systems.
SU‐F‐T‐226: QA Management for a Large Institution with Multiple Campuses for FMEA
Authors: Tang G , Chan M , Lovelock D , Lim S , Febo R , DeLauter J , Both S , Li X , Ma R , Saleh Z , Song Y , Tang X , Xiong W , Hunt M , LoSasso T 
Published: July 2016

Purpose:To redesign our radiation therapy QA program with the goal to improve quality, efficiency, and consistency among a growing number of campuses at a large institution.Methods:A QA committee was established with at least one physicist representing each of our six campuses (22 linacs). Weekly meetings were scheduled to advise on and update current procedures, to review end‐to‐end and other test results, and to prepare composite reports for internal and external audits. QA procedures for treatment and imaging equipment were derived from TG Reports 142 and 66, practice guidelines, and feedback from ACR evaluations. The committee focused on reaching a consensus on a single QA program among all campuses using the same type of equipment and reference data. Since the recommendations for tolerances referenced to baseline data were subject to interpretation in some instances, the committee reviewed the characteristics of all machines and quantified any variations before choosing between treatment planning system (i.e. treatment planning system commissioning data that is representative for all machines) or machine‐specific values (i.e. commissioning data of the individual machines) as baseline data.Results:The configured QA program will be followed strictly by all campuses. Inventory of available equipment has been compiled, and additional equipment acquisitions for the QA program are made as needed. Dosimetric characteristics are evaluated for all machines using the same methods to ensure consistency of beam data where possible. In most cases, baseline data refer to treatment planning system commissioning data but machine‐specific values are used as reference where it is deemed appropriate.Conclusion:With a uniform QA scheme, variations in QA procedures are kept to a minimum. With a centralized database, data collection and analysis are simplified. This program will facilitate uniformity in patient treatments and analysis of large amounts of QA data campus‐wide, which will ultimately facilitate FMEA.
SU‐F‐T‐227: A Comprehensive Patient Specific, Structure Specific, Pre‐Treatment 3D QA Protocol for IMRT, SBRT and VMAT ‐ Clinical Experience
Authors: Gueorguiev G , Cotter C , Young M , Toomeh D , Khan F , Crawford B , Turcotte J , Mah'D M , Sharp G 
Published: July 2016

Purpose:To present a 3D QA method and clinical results for 550 patients.Methods:Five hundred and fifty patient treatment deliveries (400 IMRT, 75 SBRT and 75 VMAT) from various treatment sites, planned on Raystation treatment planning system (TPS), were measured on three beam‐matched Elekta linear accelerators using IBA's COMPASS system. The difference between TPS computed and delivered dose was evaluated in 3D by applying three statistical parameters to each structure of interest: absolute average dose difference (AADD, 6% allowed difference), absolute dose difference greater than 6% (ADD6, 4% structure volume allowed to fail) and 3D gamma test (3%/3mm DTA, 4% structure volume allowed to fail). If the allowed value was not met for a given structure, manual review was performed. The review consisted of overlaying dose difference or gamma results with the patient CT, scrolling through the slices. For QA to pass, areas of high dose difference or gamma must be small and not on consecutive slices. For AADD to manually pass QA, the average dose difference in cGy must be less than 50cGy. The QA protocol also includes DVH analysis based on QUANTEC and TG‐101 recommended dose constraints.Results:Figures 1–3 show the results for the three parameters per treatment modality. Manual review was performed on 67 deliveries (27 IMRT, 22 SBRT and 18 VMAT), for which all passed QA. Results show that statistical parameter AADD may be overly sensitive for structures receiving low dose, especially for the SBRT deliveries (Fig.1). The TPS computed and measured DVH values were in excellent agreement and with minimum difference.Conclusion:Applying DVH analysis and different statistical parameters to any structure of interest, as part of the 3D QA protocol, provides a comprehensive treatment plan evaluation.Author G. Gueorguiev discloses receiving travel and research funding from IBA for unrelated to this project work. Author B. Crawford discloses receiving travel funding from IBA for unrelated to this project work.
SU‐F‐T‐232: Monthly Quality Assurance in External Beam Radiation Therapy Using a Single System
Authors: Ding K , Ji T , Iordachita I , Velarde E , Hyatt J , Wong J 
Published: July 2016

Purpose:Monthly quality assurance (QA) is time consuming for external beam radiation therapy, taking as long as 6–8 hours for each machine. It is due to the use and setup of multiple devices for different QA procedures. We have developed a single system with rotational capability for the measurement of both optical light and radiation which significantly reduces the time spent on Monthly QA.Methods:A single system using mirrors, a phosphor screen and a CCD camera is housed on a cylindrical motor so that it can rotate 360 degrees. For monthly QA, the system is placed on the patient couch of the medical accelerator with the plane of the phosphor screen at isocenter for all measurements. For optical QA such as optical distance indicator, room laser and light field, the optical image is collected directly with the camera. For radiation QA such as beam profile, MLC speed, picket‐fence test, collimator rotation, table rotation and gantry rotation, a brass build‐up plate is attached to the top of the phosphor screen. Two brass plates with islands of different thickness were designed for photon energy and electron energy constancy checks. Flex map, distortion map and uniformity map were developed to calibrate the motor bearing, camera/lens distortion, and the phosphor screen's measured response across the field.Results:Following the TG142 guidelines for monthly QA with our system, the overall run time is reduced from 6–8 hours to 1.5 hours. Our system's rotating design allows for quick testing of the gantry radiation isocenter test that is also independent of the sag of the gantry and the EPID.Conclusion:Our system significantly shortens the time needed for monthly QA by unifying the tests with a single system. Future work will be focused on extending the technology to Brachytherapy, IMRT and proton therapy QAs.This work is funded in part by a sponsor research grant from JPLC who owns the Raven technology. John Wong is a co‐founder of JPLC.