bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐121: Abdominal Compression Effectively Reduces the Interplay Effect and Enables Pencil Beam Scanning Proton Therapy of Liver Tumors
Authors: Souris K , Glick A , Kang M , Janssens G , Sterpin E , Lin H , McDonough J , Simone C , Solberg T , Ben‐Josef E , Lee J , Lin L 
Published: July 2016

Purpose:To study if abdominal compression can reduce breathing motion and mitigate interplay effect in pencil beam scanning proton therapy (PBSPT) treatment of liver tumors in order to better spare healthy liver volumes compared with photon therapy.Methods:Ten patients, six having large tumors initially treated with IMRT and four having small tumors treated with SBRT, were replanned for PBSPT. ITV and beam‐specific PTVs based on 4D‐CT were used to ensure target coverage in PBSPT. The use of an abdominal compression belt and volumetric repainting was investigated to mitigate the interplay effect between breathing motion and PBSPT dynamic delivery. An in‐house Matlab script has been developed to simulate this interplay effect. The dose is computed on each phase individually by sorting all spots according to their simulated delivery timing. The final dose distribution is then obtained by accumulating all dose maps to a reference phase.Results:For equivalent target coverage PBSPT reduced average healthy liver dose by 9.5% of the prescription dose compared with IMRT/SBRT. Abdominal compression of 113.2±42.2 mmHg was effective for all 10 patients and reduced average motion by 2.25 mm. As a result, the average ITV volume decreased from 128.2% to 123.1% of CTV volume. Similarly, the average beam‐specific PTV volume decreased from 193.2% to 183.3%. For 8 of the 10 patients, the average motion was reduced below 5 mm, and up to 3 repainting were sufficient to mitigate interplay. For the other two patients with larger residual motion, 4–5 repainting were needed.Conclusion:We recommend evaluation of the 4DCT motion histogram following simulation and the interplay effect following treatment planning in order to personalize the use of compression and volumetric repainting for each patient. Abdominal compression enables safe and more effective PBS treatment of liver tumors by reduction of motion and interplay effect.Kevin Souris is supported by IBA and Televie Grant from F.R.S.‐FNRS. Liyong Lin is partially supported by Varian.
SU‐F‐T‐123: The Simulated Effect of the Breath‐Hold Reproducibility Treating Locally‐Advanced Lung Cancer with Pencil Beam Scanned Proton Therapy
Authors: Dueck J , Perrin R , Persson G F , Lomax A , Josipovic M , Engelholm S A , Weber D C , Munck P , Rosenschöld AF 
Published: July 2016

Purpose:The breath‐hold (BH) technique has been suggested to mitigate motion and reduce target coverage degradation due to motion effects. The aim of this study was to investigate the effect of inter‐BH residual motion on the dose distribution for pencil beam scanned (PBS) proton therapy of locally‐advanced lung cancer patients.Methods:A dataset of visually‐guided BH CT scans was acquired (10 scans per patient) taken from five lung cancer patients: three intra‐fractionally repeated CT scans on treatment days 2,16 and 31, in addition to the day 0 planning CT scan. Three field intensity‐modulated proton therapy (IMPT) plans were constructed on the planning CT scan. Dose delivery on fraction 2, 16 and 31 were simulated on the three consecutive CT scans, assuming BH duration of 20s and soft tissue match. The dose was accumulated in the planning CT using deformable image registration, and scaled to simulate the full treatment of 66Gy(RBE) in 33 fractions.Results:The mean dose to the lungs and heart, and maximum dose to the spinal cord and esophagus were within 1% of the planned dose. The CTV V95% decreased and the inhomogeneity (D5%–D95%) increased on average 4.1% (0.4–12.2%) and 5.8% (2.2–13.4%), respectively, over the five patient cases.Conclusion:The results showed that the BH technique seems to spare the OARs in spite of inter‐BH residual motion. However, small degradation of target coverage occurred for all patients, with 3/5 patients having a decrease in V95% ≤1%. For the remaining two patients, where V95% decreased up to 12%, the cause could be related to treatment related anatomical changes and, as in photon therapy, plan adaptation may be necessary to ensure target coverage. This study showed that BH could be a potential treatment option to reliably mitigate motion for the treatment of locally‐advanced lung cancer using PBS proton therapy.
SU‐F‐T‐131: No Increase in Biological Effectiveness Through Collimator Scattered Low Energy Protons
Authors: Matsuura T , Takao S , Matsuzaki Y , Fujii Y , Fujii T , Maeda K , Ueda H , Koyano H , Umegaki K , Shirato H 
Published: July 2016

Purpose:To reduce the lateral penumbra of low‐energy proton beams, brass collimators are often used in spot‐scanning proton therapy (SSPT). This study investigates the increase in biological effectiveness through collimator scattered protons in SSPT.Methods:The SSPT system of the Hokkaido University Hospital Proton Beam Therapy Center, which consists of a scanning nozzle, a 2‐cm thick brass collimator, and a 4‐cm thick energy absorber, was simulated with our validated Geant4 Monte Carlo code (ver. 9.3). A water phantom was irradiated with proton pencil beams of 76, 110, and 143 MeV. The tested collimator opening areas (COA) were 5×5, 10×10, and 15×15 cm2. Comparisons were made among the dose‐averaged LET values of protons that hit the collimators (LETDColl), protons that did not hit the collimators (LETDNoColl), and all protons (LETDTotal). X‐ray equivalent doses (Deq) were calculated using the linear‐quadratic model with LETDNoColl and LETDTotal, and their maximum difference was determined over regions where the physical dose was greater than 10% of the peak dose of 2 Gy.Results:The ratio of the dose contribution of collimator scattered protons to that of all protons, defined as λ, was large at high proton energies and large COAs. The maximum λ value ranged from 3% (76 MeV, 5×5 cm2) to 29% (143 MeV, 15×15 cm2). Moreover, a large difference between LETDColl and LETDNoColl was only found in regions where λ was below 20% (ΔLETD > 2 keV/µm) and 8% (ΔLETD > 5 keV/µm). Consequently, the maximum difference between LETDNoColl and LETDTotal was as small as 0.8 keV/µm in all simulated voxels, and the difference of Deq reached a maximum of 1.5% that of the peak dose obtained at the water surface with a 76 MeV beam.Conclusion:Although collimator scattered protons have high LET, they only increase the physical dose, not the biological effectiveness.
SU‐F‐T‐147: An Alternative Parameterization of Scatter Behavior Allows Significant Reduction of Beam Characterization for Pencil Beam Proton Therapy
Authors: Van den Heuvel F , Fiorini F , George B 
Published: July 2016

Purpose:1) To describe the characteristics of pencil beam proton dose deposition kernels in a homogenous medium using a novel parameterization. 2) To propose a method utilizing this novel parametrization to reduce the measurements and pre‐computation required in commissioning a pencil beam proton therapy system.Methods:Using beam data from a clinical, pencil beam proton therapy center, Monte Carlo simulations were performed to characterize the dose depositions at a range of energies from 100.32 to 226.08 MeV in 3.6MeV steps. At each energy, the beam is defined at the surface of the phantom by a two‐dimensional Normal distribution. Using FLUKA, the in‐medium dose distribution is calculated in 200×200×350 mm cube with 1 mm3 tally volumes. The calculated dose distribution in each 200×200 slice perpendicular to the beam axis is then characterized using a symmetric alpha‐stable distribution centered on the beam axis. This results in two parameters, α and γ, that completely describe shape of the distribution. In addition, the total dose deposited on each slice is calculated. The alpha‐stable parameters are plotted as function of the depth in‐medium, providing a representation of dose deposition along the pencil beam. We observed that these graphs are isometric through a scaling of both abscissa and ordinate map the curves.Results:Using interpolation of the scaling factors of two source curves representative of different beam energies, we predicted the parameters of a third curve at an intermediate energy. The errors are quantified by the maximal difference and provide a fit better than previous methods. The maximal energy difference between the source curves generating identical curves was 21.14MeV.Conclusion:We have introduced a novel method to parameterize the in‐phantom properties of pencil beam proton dose depositions. For the case of the Knoxville IBA system, no more than nine pencil beams have to be fully characterized.
SU‐F‐T‐153: Experimental Validation and Calculation Benchmark for a Commercial Monte Carlo Pencil Beam Scanning Proton Therapy Treatment Planning System in Water
Authors: Lin L , Huang S , Kang M , Ainsley C , Hiltunen P , Vanderstraeten R , Lindberg J , Siljamaki S , Wareing T , Davis I , Barnett A , McGhee J , Solberg T , McDonough J , Simone C 
Published: July 2016

Purpose:Eclipse proton Monte Carlo AcurosPT 13.7 was commissioned and experimentally validated for an IBA dedicated PBS nozzle in water. Topas 1.3 was used to isolate the cause of differences in output and penumbra between simulation and experiment.Methods:The spot profiles were measured in air at five locations using Lynx. PTW‐34070 Bragg peak chamber (Freiburg, Germany) was used to collect the relative integral Bragg peak for 15 proton energies from 100 MeV to 225 MeV. The phase space parameters (σx, σθ, ρxθ) number of protons per MU, energy spread and calculated mean energy provided by AcurosPT were identically implemented into Topas. The absolute dose, profiles and field size factors measured using ionization chamber arrays were compared with both AcurosPT and Topas.Results:The beam spot size, σx, and the angular spread, σθ, in air were both energy‐dependent: in particular, the spot size in air at isocentre ranged from 2.8 to 5.3 mm, and the angular spread ranged from 2.7 mrad to 6 mrad. The number of protons per MU increased from ∼9E7 at 100 MeV to ∼1.5E8 at 225 MeV. Both AcurosPT and TOPAS agree with experiment within 2 mm penumbra difference or 3% dose difference for scenarios including central axis depth dose and profiles at two depths in multi‐spot square fields, from 40 to 200 mm, for all the investigated single‐energy and multi‐energy beams, indicating clinically acceptable source model and radiation transport algorithm in water.Conclusion:By comparing measured data and TOPAS simulation using the same source model, the AcurosPT 13.7 was validated in water within 2 mm penumbra difference or 3% dose difference. Benchmarks versus an independent Monte Carlo code are recommended to study the agreement in output, filed size factors and penumbra differences.This project is partially supported by the Varian grant under the master agreement between University of Pennsylvania and Varian
SU‐F‐T‐161: The Effect of Pencil Beam Scanning Gantry Angle Dependent Spot Size Variations On Plan Quality
Authors: Langner U , Langen K 
Published: July 2016

Purpose:To investigate the effect of spot size variation as function of gantry angle on the quality of treatment plans for pencil beam scanning proton plans.Method:Three homogeneous 26×26×7cm dose volumes with different ranges and SOBPs were delivered on the matrixxPT 2D array at gantry angles of 0 and 270 degrees. The spot size sigma varies by 1.8, 7.8, and 1.4%, for nominal energies of 215, 183, and 103 MeV (Range 29, 22, and 8cm, respectively). The resulting dose planes are compared and evaluated with the gamma index for 2%/2mm and 1%/1mm criteria.Results:Patient specific QA is performed at a gantry angle of 0 degrees. However, beam sigmas vary as function of gantry angle because of the beam optics for each gantry. This will cause differences between the delivered and planned treatment plans. Delivered plans were compared and a gamma pass rate of 96.5% for criteria of 2%/2mm and 91.4% for 1%/1mm were seen for plans with a nominal energy of 183 MeV. For plans with a nominal energy of 103 MeV, gamma pass rates of 97.3% for 2%/2mm and 91.5% for 1%/1mm were seen. For plans with a nominal energy of 215 MeV the pass rate was 99.8% for 1%/1mm between the two gantry angles.Conclusion:Differences in beam sigma of up to 7.8% do not cause significant differences in the dose distribution of different spot size gammas.
SU‐F‐T‐170: Patient Surface Dose Measurements Using Optically Stimulated Luminescence Dosimeters in Scanning Proton Beam Therapy for Breast Cancer
Authors: Yu J , Strauss D , Langner U , Langen K 
Published: July 2016

Purpose:To establish patient surface dose dosimetry for scanning proton beam therapy (SPBT) for breast cancer using optically stimulated luminescence dosimeters (OSLD).Methods:OSLDs were calibrated with SPB under the similar conditions as the treatments for breast cancer. A range shifter (RS) of 5 cm water equivalent thickness (WET) was used. The air gap from the surface of the range shifter to the surface of the phantom was 15 cm. A uniform planar dose generated by nominal energy of 118 MeV was delivered. The range of 118 MeV proton beam after the 5cm RS is approximately 5 cm in water, which is the common range for breast treatments. The OSLDs were placed on the surface of high density polyethylene slabs, and a bolus of 1.06 cm WET was used for buildup. A variety of dose levels in the range of 0.5 to 8 Gy were delivered. Under the same condition, an ADCL calibrated parallel plate (PP) chamber was used to measure the reference dose. The correlation between the output signals of OSLDs and the reference doses was established. The calibration of OSLD was verified against the PP chamber measurements for two SPBT breast plans calculated for two patients.Results:the least squares fitting for the OSLD calibration curve was a polynomial function to the order of 2 in the range of 0.5 to 8 Gy (RBE). The differences between the dose measured with OSLDs and PP chamber were within 3% for the two breast proton plans.Conclusion:the calibrated OSLDs under the similar conditions as the treatments can be used for patient surface dose measurements.
SU‐F‐T‐172: A Method for Log File QA On An IBA Proteus System for Patient Specific Spot Scanning Quality Assurance
Authors: Tang S , Ho M , Rice I , Doan D , Chen C , Mac Rae B , Mah D 
Published: July 2016

Purpose:The use of log files to perform patient specific quality assurance for both protons and IMRT has been established. Here, we extend that approach to a proprietary log file format and compare our results to measurements in phantom. Our goal was to generate a system that would permit gross errors to be found within 3 fractions until direct measurements. This approach could eventually replace direct measurements.Methods:Spot scanning protons pass through multi‐wire ionization chambers which provide information about the charge, location, and size of each delivered spot. We have generated a program that calculates the dose in phantom from these log files and compares the measurements with the plan. The program has 3 different spot shape models: single Gaussian, double Gaussian and the ASTROID model. The program was benchmarked across different treatment sites for 23 patients and 74 fields.Results:The dose calculated from the log files were compared to those generate by the treatment planning system (Raystation). While the dual Gaussian model often gave better agreement, overall, the ASTROID model gave the most consistent results. Using a 5%–3 mm gamma with a 90% passing criteria and excluding doses below 20% of prescription all patient samples passed. However, the degree of agreement of the log file approach was slightly worse than that of the chamber array measurement approach. Operationally, this implies that if the beam passes the log file model, it should pass direct measurement.Conclusion:We have established and benchmarked a model for log file QA in an IBA proteus plus system. The choice of optimal spot model for a given class of patients may be affected by factors such as site, field size, and range shifter and will be investigated further.
SU‐F‐T‐182: A Stochastic Approach to Daily QA Tolerances On Spot Properties for Proton Pencil Beam Scanning
Authors: St. James S , Saini J , Bloch C 
Published: July 2016

Purpose:Proton pencil beam scanning is used clinically across the United States. There are no current guidelines on tolerances for daily QA specific to pencil beam scanning, specifically related to the individual spot properties (spot width). Using a stochastic method to determine tolerances has the potential to optimize tolerances on individual spots and decrease the number of false positive failures in daily QA. Individual and global spot tolerances were evaluated.Methods:As part of daily QA for proton pencil beam scanning, a field of 16 spots (corresponding to 8 energies) is measured using an array of ion chambers (Matrixx, IBA). Each individual spot is fit to two Gaussian functions (x,y). The spot width (σ) in × and y are recorded (32 parameters). Results from the daily QA were retrospectively analyzed for 100 days of data. The deviations of the spot widths were histogrammed and fit to a Gaussian function. The stochastic spot tolerance was taken to be the mean ± 3σ. Using these results, tolerances were developed and tested against known deviations in spot width.Results:The individual spot tolerances derived with the stochastic method decreased in 30/32 instances. Using the previous tolerances (± 20% width), the daily QA would have detected 0/20 days of the deviation. Using a tolerance of any 6 spots failing the stochastic tolerance, 18/20 days of the deviation would have been detected.Conclusion:Using a stochastic method we have been able to decrease daily tolerances on the spot widths for 30/32 spot widths measured. The stochastic tolerances can lead to detection of deviations that previously would have been picked up on monthly QA and missed by daily QA. This method could be easily extended for evaluation of other QA parameters in proton spot scanning.
SU‐F‐T‐183: Design of a Beam Shaping Assembly of a Compact DD‐Based Boron Neutron Capture Therapy System
Authors: Hsieh M , Liu Y , Nie L 
Published: July 2016

Purpose:To design a beam shaping assembly (BSA) to shape the 2.45‐MeV neutrons produced by a deuterium‐deuterium (DD) neutron generator and to optimize the beam output for boron neutron capture therapy of brain tumorsMethods:MCNP is used for this simulation study. The simulation model consists of a neutron surface source that resembles an actual DD source and is surrounded by a BSA. The neutron source emits 2.45‐MeV neutrons isotropically. The BSA is composed of a moderator, reflector, collimator and filter. Various types of materials and geometries are tested for each component to optimize the neutron output. Neutron characteristics are measured with an 2×2×2‐cm3 air‐equivalent cylinder at the beam exit. The ideal BSA is determined by evaluating the in‐air parameters, which include epithermal neutron per source neutron, fast neutron dose per epithermal neutron, and photon dose per epithermal neutron. The parameter values are compared to those recommended by the IAEA.Results:The ideal materials for reflector and thermal neutron filter were lead and cadmium, respectively. The thickness for reflector was 43 cm and for filter was 0.5 mm. At present, the best‐performing moderator has 25 cm of AlF3 and 5 cm of MgF2. This layout creates a neutron spectrum that has a peak at approximately 10 keV and produces 1.35E‐4 epithermal neutrons per source neutron per cm2. Additional neutron characteristics, fast neutrons per epithermal neutron and photon per epithermal neutron, are still under investigation.Conclusion:Working is ongoing to optimize the final layout of the BSA. The neutron spectrum at the beam exit window of the final configuration will have the maximum number of epithermal neutrons and limited photon and fast neutron contaminations within the recommended values by IAEA. Future studies will also include phantom experiments to validate the simulation results.
SU‐F‐T‐184: 3D Range‐Modulator for Scanned Particle Therapy: Development, Monte Carlo Simulations and Measurements
Authors: Simeonov Y , Penchev P , Ringbaek T Printz , Brons S , Weber U , Zink K 
Published: July 2016

Purpose:Active raster scanning in particle therapy results in highly conformal dose distributions. Treatment time, however, is relatively high due to the large number of different iso‐energy layers used. By using only one energy and the so called 3D range‐modulator irradiation times of a few seconds only can be achieved, thus making delivery of homogeneous dose to moving targets (e.g. lung cancer) more reliable.Methods:A 3D range‐modulator consisting of many pins with base area of 2.25 mm2 and different lengths was developed and manufactured with rapid prototyping technique. The form of the 3D range‐modulator was optimised for a spherical target volume with 5 cm diameter placed at 25 cm in a water phantom. Monte Carlo simulations using the FLUKA package were carried out to evaluate the modulating effect of the 3D range‐modulator and simulate the resulting dose distribution. The fine and complicated contour form of the 3D range‐modulator was taken into account by a specially programmed user routine. Additionally FLUKA was extended with the capability of intensity modulated scanning. To verify the simulation results dose measurements were carried out at the Heidelberg Ion Therapy Center (HIT) with a 400.41 MeV 12C beam.Results:The high resolution measurements show that the 3D range‐modulator is capable of producing homogeneous 3D conformal dose distributions, simultaneously reducing significantly irradiation time. Measured dose is in very good agreement with the previously conducted FLUKA simulations, where slight differences were traced back to minor manufacturing deviations from the perfect optimised form.Conclusion:Combined with the advantages of very short treatment time the 3D range‐modulator could be an alternative to treat small to medium sized tumours (e.g. lung metastasis) with the same conformity as full raster‐scanning treatment. Further simulations and measurements of more complex cases will be conducted to investigate the full potential of the 3D range‐modulator.