bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐157: Physics Considerations Regarding Dosimetric Accuracy of Analytical Dose Calculations for Small Field Proton Therapy: A Monte Carlo Study
Authors: Geng C , Daartz J , Cheung K , Bussiere M , Shih H , Paganetti H , Schuemann J 
Published: July 2016

Purpose:To evaluate the accuracy of dose calculations by analytical dose calculation methods (ADC) for small field proton therapy in a gantry based passive scattering facility. Methods: 50 patients with intra‐cranial disease were evaluated in the study. Treatment plans followed standard prescription and optimization procedures of proton stereotactic radiosurgery. Dose distributions calculated with the Monte Carlo (MC) toolkit TOPAS were used to represent delivered treatments. The MC dose was first adjusted using the output factor (OF) applied clinically. This factor is determined from the field size and the prescribed range. We then introduced a normalization factor to measure the difference in mean dose between the delivered dose (MC dose with OF) and the dose calculated by ADC for each beam. The normalization was determined by the mean dose of the center voxels of the target area. We compared delivered dose distributions and those calculated by ADC in terms of dose volume histogram parameters and beam range distributions.Results:The mean target dose for a whole treatment is generally within 5% comparing delivered dose (MC dose with OF) and ADC dose. However, the differences can be as great as 11% for shallow and small target treated with a thick range compensator. Applying the normalization factor to the MC dose with OF can reduce the mean dose difference to less than 3%. Considering range uncertainties, the generally applied margins (3.5% of the prescribed range + 1mm) to cover uncertainties in range might not be sufficient to guarantee tumor coverage. The range difference for R90 (90% distal dose falloff) is affected by multiple factors, such as the heterogeneity index.Conclusion:This study indicates insufficient accuracy calculating proton doses using ADC. Our results suggest that uncertainties of target doses are reduced using MC techniques, improving the dosimetric accuracy for proton stereotactic radiosurgery.The work was supported by NIH/NCI under CA U19 021239. CG was partially supported by the Chinese Scholarship Council (CSC) and the National Natural Science Foundation of China (Grant No. 11475087).
SU‐F‐T‐158: Experimental Characterization of Field Size Dependence of Dose and Lateral Beam Profiles of Scanning Proton and Carbon Ion Beams for Empirical Model in Air
Authors: Li Y , Hsi W , Zhao J 
Published: July 2016

Purpose:The Gaussian model for the lateral profiles in air is crucial for an accurate treatment planning system. The field size dependence of dose and the lateral beam profiles of scanning proton and carbon ion beams are due mainly to particles undergoing multiple Coulomb scattering in the beam line components and secondary particles produced by nuclear interactions in the target, both of which depend upon the energy and species of the beam. In this work, lateral profile shape parameters were fitted to measurements of field size dependence dose at the center of field size in air.Methods:Previous studies have employed empirical fits to measured profile data to significantly reduce the QA time required for measurements. From this approach to derive the weight and sigma of lateral profiles in air, empirical model formulations were simulated for three selected energies for both proton and carbon beams.Results:The 20%–80% lateral penumbras predicted by the double model for proton and single model for carbon with the error functions agreed with the measurements within 1 mm. The standard deviation between measured and fitted field size dependence of dose for empirical model in air has a maximum accuracy of 0.74% for proton with double Gaussian, and of 0.57% for carbon with single Gaussian.Conclusion:We have demonstrated that the double Gaussian model of lateral beam profiles is significantly better than the single Gaussian model for proton while a single Gaussian model is sufficient for carbon. The empirical equation may be used to double check the separately obtained model that is currently used by the planning system. The empirical model in air for dose of spot scanning proton and carbon ion beams cannot be directly used for irregular shaped patient fields, but can be to provide reference values for clinical use and quality assurance.
SU‐F‐T‐159: Monte Carlo Simulation Studies of Three‐Dimensional Dose Distribution for Polymer Gel Dosimeter and Radiochromic Gel Dosimeter in a Proton Beam
Authors: Park M , Kim G , Jung H , Park S , Park S , Ji Y , Yun J 
Published: July 2016

Purpose:The purpose of this simulation study is to evaluate the proton detectability of gel dosimeters, and estimate the three‐dimensional dose distribution of protons in the radiochromic gel and polymer gel dosimeter compared with the dose distribution in water.Methods:The commercial composition ratios of normoxic polymer gel and LCV micelle radiochromic gel were included in this simulation study. The densities of polymer and radiochromic gel were 1.024 and 1.005 g/cm3, respectively. The 50, 80 and 140 MeV proton beam energies were selected. The dose distributions of protons in the polymer and radiochromic gel were simulated using Monte Carlo radiation transport code (MCNPX 2.7.0, Los Alamos Laboratory). The water equivalent depth profiles and the dose distributions of two gel dosimeters were compared for the water.Results:In case of irradiating 50, 80 and 140 MeV proton beam to water phantom, the reference Bragg‐peak depths are represented at 2.22, 5.18 and 13.98 cm, respectively. The difference in the water equivalent depth is represented to about 0.17 and 0.37 cm in the radiochromic gel and polymer gel dosimeter, respectively. The proton absorbed doses in the radiochromic gel dosimeter are calculated to 2.41, 3.92 and 6.90 Gy with increment of incident proton energies. In the polymer gel dosimeter, the absorbed doses are calculated to 2.37, 3.85 and 6.78 Gy with increment of incident proton energies. The relative absorbed dose in radiochromic gel (about 0.47 %) is similar to that of water than the relative absorbed dose of polymer gel (about 2.26 %). In evaluating the proton dose distribution, we found that the dose distribution of both gel dosimeters matched that of water in most cases.Conclusion:As the dosimetry device, the radiochromic gel dosimeter has the potential particle detectability and is feasible to use for quality assurance of proton beam therapy beam.
SU‐F‐T‐162: Comparison of Beam Data for Two Varian ProBeam Pencil Beam Scanning Proton Systems
Authors: Langner U , Langen K , Eley J , Zhu M , Yu J , Chung H , Polf J , Dong L 
Published: July 2016

Purpose:To compare the beam data for proton spot scanning beams for the first two Varian ProBeam sites in the US at the Maryland Proton Treatment Center (MPTC) and Scripps Proton Therapy Center (Scripps). To investigate how well beams can be matched between rooms.Method:Beam data were acquired with independent dosimetry systems and compared for two sites. Integrated depth dose curves (IDDs) were acquired with large volume PTW Bragg peak chambers in a 3D water tank for pencil beams at both sites. Spot profiles were acquired at different distances from the isocenter at a gantry angle of 0 degrees as well as function of gantry angle.Results:IDDs for the two Varian ProBeam proton sites are similar, except in the plateau region were the Scripps data is on average 4.5% higher relative to each other, but only 1.5% relative to the maximum at the Bragg Peak. This increase in the plateau region decrease as energy increase and for energies larger than 180 MeV there is no marked difference. Range in water coincide for all energies within 0.5mm. The sigma of the spot profiles in air are within 10% of each other at isocenter. This difference increase as the detector distance from the isocenter is increased.Conclusion:Beam data of the Varian ProBeam proton spot scanning beams for two sites are very well matched. Differences will not be clinically relevant.
SU‐F‐T‐165: Daily QA Analysis for Spot Scanning Beamline
Authors: Poenisch F , Gillin M , Sahoo N , Martin C , Zhu X 
Published: July 2016

Purpose:The dosimetric results of our daily quality assurance over the last 8 years for discrete pencil beam scanning proton therapy will be presented.Methods:To perform the dosimetric checks, a multi‐ion chamber detector is used, which consists of an array of 5 single parallel plate ion chambers that are aligned as a cross separated by 10cm each. The Tracker is snapped into a jig, which is placed on the tabletop. Different amounts of Solid Water buildup are added to shift the dose distribution. The dosimetric checks consist of 3 parts: position check, range check and volume dose check.Results:The average deviation of all position‐check data were 0.2±1.3%. For the range check, the average deviation was 0.1%±1.2%, which also corresponds to a range stability of better than 1 mm over all measurements. The volumetric dose output readings were all within ±1% with the exception of 2 occasions when the cable to the dose monitor was being repaired.Conclusion:Morning QA using the Tracker device gives very stable dosimetric readings but is also sensitive to mechanical and output changes in the proton therapy delivery system.
SU‐F‐T‐166: On the Nature of the Background Visible Light Observed in Fiber Optic Dosimetry of Proton Beams
Authors: Darafsheh A , Taleei R , Kassaee A , Finlay J 
Published: July 2016

Purpose:The nature of the background visible light observed during fiber optic dosimetry of proton beams, whether it is due to Cherenkov radiation or not, has been debated in the literature recently. In this work, experimentally and by means of Monte Carlo simulations, we shed light on this problem and investigated the nature of the background visible light observed in fiber optics irradiated with proton beams.Methods:A bare silica fiber optics was embedded in tissue‐mimicking phantoms and irradiated with clinical proton beams with energies of 100–225 MeV at Roberts Proton Therapy Center. Luminescence spectroscopy was performed by a CCD‐coupled spectrograph to analyze in detail the emission spectrum of the fiber tip across the visible range of 400–700 nm. Monte Carlo simulation was performed by using FLUKA Monte Carlo code to simulate Cherenkov light and ionizing radiation dose deposition in the fiber.Results:The experimental spectra of the irradiated silica fiber shows two distinct peaks at 450 and 650 nm, whose spectral shape is different from that of Cherenkov radiation. We believe that the nature of these peaks are connected to the point defects of silica including oxygen‐deficiency center (ODC) and non‐bridging oxygen hole center (NBOHC). Monte Carlo simulations confirmed the experimental observations that Cherenkov radiation cannot be solely responsible for such a signal.Conclusion:We showed that Cherenkov radiation is not the dominant visible signal observed in bare fiber optics irradiated with proton beams. We observed two distinct peaks at 450 and 650 nm whose nature is connected with the point defects of silica fiber including oxygen‐deficiency center and non‐bridging oxygen hole center.
SU‐F‐T‐167: Measurement of Proton Beam Spot Size Using a 2D Ion Chamber Array for Daily QA
Authors: Thorne N , Kassaee A 
Published: July 2016

Purpose:To develop an algorithm which can calculate the Full Width Half Maximum (FWHM) of a Proton Pencil Beam from a 2D dimensional ion chamber array (IBA Matrixx) with limited spatial resolution (7.6 mm inter chamber distance). The algorithm would allow beam FWHM measurements to be taken during daily QA without an appreciable time increase.Methods:Combinations of 147 MeV single spot beams were delivered onto an IBA Matrixx and concurrently on EBT3 films for a standard. Data were collected around the Bragg Peak region and evaluated by a custom MATLAB script based on our algorithm using a least squared analysis. A set of artificial data, modified with random noise, was also processed to test for robustness.Results:The Matlab script processed Matixx data shows acceptable agreement (within 5%) with film measurements with no single measurement differing by more than 1.8 mm. In cases where the spots show some degree of asymmetry, the algorithm is able to resolve the differences. The algorithm was able to process artificial data with noise up to 15% of the maximum value. Time assays of each measurement took less than 3 minutes to perform, indicating that such measurements may be efficiently added to daily QA treatment.Conclusion:The developed algorithm can be implemented in daily QA program for Proton Pencil Beam scanning beams (PBS) with Matrixx to extract spot size and position information. The developed algorithm may be extended to small field sizes in photon clinic.
SU‐F‐T‐168: Development and Implementation of An Anthropomorphic Head & Neck Phantom for the Assessment of Proton Therapy Treatment Procedures
Authors: Branco D , Taylor P , Frank S , Li H , Zhang X , Mehrens H , Guindani M , Followill D 
Published: July 2016

Purpose:To design a Head and Neck (H&N) anthropomorphic QA phantom that the Imaging and Radiation Oncology Core Houston (IROC‐H) can use to verify the quality of intensity modulated proton therapy (IMPT) H&N treatments for institutions participating in NCI clinical trials.Methods:The phantom was created to serve as a remote auditing tool for IROC‐H to evaluate an institution's IMPT planning and delivery abilities. The design was based on the composition, size, and geometry of a generalized oropharyngeal tumor and contains critical structures (parotids and spinal cord). Radiochromic film in the axial and sagittal planes and thermoluminescent dosimeters (TLD)‐100 capsules were embedded in the phantom and used to perform the dose delivery evaluation. A CT simulation was used to create a passive scatter and a spot scanning treatment plan with typical clinical constraints for H&N cancer. The IMPT plan was approved by a radiation oncologist and the phantom was irradiated multiple times. The measured dose distribution using a 7%/4mm gamma analysis (85% of pixels passing) and point doses were compared with the treatment planning system calculations.Results:The designed phantom could not achieve the target dose prescription and organ at risk dose constraints with the passive scatter treatment plan. The target prescription dose could be met but not the parotid dose constraint. The average TLD point dose ratio in the target was 0.975, well within the 5% acceptance criterion. The dose distribution analysis using various acceptance criteria, 5%/4mm, 5%/3mm, 7%/4mm and 7%/5mm, had average pixel passing rates of 85.9%, 81.8%, 89.6% and 91.6%, and respectively.Conclusion:An anthropomorphic IMPT H&N phantom was designed that can assess the dose delivery of proton sites wishing to participate in clinical trials using a 5% TLD dose and 7%/4mm gamma analysis acceptance criteria.
SU‐F‐T‐173: One‐Scan Protocol: Verifying the Delivery of Spot‐Scanning Proton Beam
Authors: Chan M , Chen C , Li J , Tang X , Li X , Tang G , Mah D 
Published: July 2016

Purpose:Radiochromic film for spot‐scanning QA provides high spatial resolution and efficiency gains from one‐shot irradiation for multiple depths. However, calibration can be a tedious procedure which may limit widespread use. Moreover, since there may be an energy dependence, which manifests as a depth dependence, this may require additional measurements for each patient. We present a one‐scan protocol to simplify the procedure.Methods:We performed the calibration using an EBT3 film at depths of 18, 20, 24cm of Plastic Water exposed by a 6‐level step‐wedge plan on a Proteus Plus proton system (IBA, Belgium). The calibration doses ranged 65–250 cGy(RBE) for proton energies of 170–200MeV. A clinical prostate+nodes plan was used for validation. The planar doses at selected depths were measured with EBT3 films and analyzed using one‐scan protocol (one‐scan digitization of QA film and at least one film exposed to known dose). The Gamma passing rates, dose‐difference maps, and profiles of 2D planar doses measured with EBT3 film, IBA MatriXX PT, versus TPS calculations were analyzed and compared.Results:The EBT3 film measurement results matched well with the TPS calculation data with an average passing rate of ∼95% for 2%/2mm and slightly lower passing rates were obtained from an ion chamber array detector. We were able to demonstrate that the use of a proton step‐wedge provided clinically acceptable results and minimized variations between film‐scanner orientation, inter‐scan, and scanning conditions. Furthermore, it could be derived from no more than two films exposed to known doses (one could be zero) for rescaling the master calibration curve at each depth.Conclusion:The use of a proton step‐wedge for calibration of EBT3 film increases efficiency. The sensitivity of the calibration to depth variations has been explored. One‐scan protocol results appear to be comparable to that of the ion chamber array detector.One author has a research grant from Ashland Inc., the manufacturer of the GafChromic film.
SU‐F‐T‐177: Impacts of Gantry Angle Dependent Scanning Beam Properties for Proton Treatment
Authors: Lin Y , Clasie B , Lu H , Flanz J , Jee K 
Published: July 2016

Purpose:In pencil beam scanning (PBS), the delivered spot MU, position and size are slightly different at different gantry angles. We investigated the level of delivery uncertainty at different gantry angles through a log file analysis.Methods:34 PBS fields covering full 360 degrees gantry angle spread were collected retrospectively from 28 patients treated at our institution. All fields were delivered at zero gantry angle and the prescribed gantry angle, and measured at isocenter with the MatriXX 2D array detector at the prescribed gantry angle. The machine log files were analyzed to extract the delivered MU per spot and the beam position from the strip ionization chambers in the treatment nozzle. The beam size was separately measured as a function of gantry angle and beam energy. Using this information, the dose was calculated in a water phantom at both gantry angles and compared to the measurement using the 3D γ‐index at 2mm/2%.Results:The spot‐by‐spot difference between the beam position in the log files from the delivery at the two gantry angles has a mean of 0.3 and 0.4 mm and a standard deviation of 0.6 and 0.7 mm for × and y directions, respectively. Similarly, the spot‐by‐spot difference between the MU in the log files from the delivery at the two gantry angles has a mean 0.01% and a standard deviation of 0.7%. These small deviations lead to an excellent agreement in dose calculations with an average γ pass rate for all fields being approximately 99.7%. When each calculation is compared to the measurement, a high correlation in γ was also found.Conclusion:Using machine logs files, we verified that PBS beam delivery at different gantry angles are sufficiently small and the planned spot position and MU. This study brings us one step closer to simplifying our patient‐specific QA.
SU‐F‐T‐181: Proton Therapy Tissue‐Equivalence of 3D Printed Materials
Authors: Taylor P , Craft D , Followill D , Howell R 
Published: July 2016

Purpose:This work investigated the proton tissue‐equivalence of various 3D printed materials.Methods:Three 3D printers were used to create 5 cm cubic phantoms made of different plastics with varying percentages of infill. White resin, polylactic acid (PLA), and NinjaFlex plastics were used. The infills ranged from 15% to 100%. Each phantom was scanned with a CT scanner to obtain the HU value. The relative linear stopping power (RLSP) was then determined using a multi‐layer ion chamber in a 200 MeV proton beam. The RLSP was measured both parallel and perpendicular to the print direction for each material.Results:The HU values of the materials ranged from lung‐equivalent (−820 HU σ160) when using a low infill, to soft‐tissue‐equivalent 159 (σ12). The RLSP of the materials depended on the orientation of the beam relative to the print direction. When the proton beam was parallel to the print direction, the RLSP was generally higher than the RLSP in the perpendicular orientation, by up to 45%. This difference was smaller (less than 6%) for the materials with 100% infill. For low infill cubes irradiated parallel to the print direction, the SOBP curve showed extreme degradation of the beam in the distal region. The materials with 15–25% infill had wide‐ranging agreement with a clinical HU‐RLSP conversion curve, with some measurements falling within 1% of the curve and others deviating up to 45%. The materials with 100% infill all fell within 7% of the curve.Conclusion:While some materials tested fall within 1% of a clinical HU‐RLSP curve, caution should be taken when using 3D printed materials with proton therapy, as the orientation of the beam relative to the print direction can result in a large change in RLSP. Further investigation is needed to measure how the infill pattern affects the material RLSP.This work was supported by PHS grant CA180803.
SU‐F‐T‐188: A Robust Treatment Planning Technique for Proton Pencil Beam Scanning Cranial Spinal Irradiation
Authors: Zhu M , Yam M , Mehta M , Badiyan S , Young K , Malyapa R , Regine W , Langen K 
Published: July 2016

Purpose:To propose a proton pencil beam scanning (PBS) cranial spinal irradiation (CSI) treatment planning technique robust against patient roll, isocenter offset and proton range uncertainty.Method:Proton PBS plans were created (Eclipse V11) for three previously treated CSI patients to 36 Gy (1.8 Gy/fractions). The target volume was separated into three regions: brain, upper spine and lower spine. One posterior‐anterior (PA) beam was used for each spine region, and two posterior‐oblique beams (15° apart from PA direction, denoted as 2PO_15) for the brain region. For comparison, another plan using one PA beam for the brain target (denoted as 1PA) was created. Using the same optimization objectives, 98% CTV was optimized to receive the prescription dose. To evaluate plan robustness against patient roll, the gantry angle was increased by 3° and dose was recalculated without changing the proton spot weights. On the re‐calculated plan, doses were then calculated using 12 scenarios that are combinations of isocenter shift (±3mm in X, Y, and Z directions) and proton range variation (±3.5%). The worst‐case‐scenario (WCS) brain CTV dosimetric metrics were compared to the nominal plan.Results:For both beam arrangements, the brain field(s) and upper‐spine field overlap in the T2–T5 region depending on patient anatomy. The maximum monitor unit per spot were 48.7%, 47.2%, and 40.0% higher for 1PA plans than 2PO_15 plans for the three patients. The 2PO_15 plans have better dose conformity. At the same level of CTV coverage, the 2PO_15 plans have lower maximum dose and higher minimum dose to the CTV. The 2PO_15 plans also showed lower WCS maximum dose to CTV, while the WCS minimum dose to CTV were comparable between the two techniques.Conclusion:Our method of using two posterior‐oblique beams for brain target provides improved dose conformity and homogeneity, and plan robustness including patient roll.