bluuebunny/crossref_metadata_2025 huggingface dataset:
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‐154: An Evaluation and Quantification of Secondary Neutron Radiation Dose Due to Double Scatter and Pencil Beam Scanning Proton Therapy
Authors: Glick A , Diffenderfer E
Published: July 2016

Proton radiation therapy can deliver high radiation doses to tumors while sparing normal tissue. However, protons yield secondary neutron and gamma radiation that is difficult to detect, small in comparison to the prescribed dose, and not accounted for in most treatment planning systems. The risk for secondary malignancies after proton therapy may be dependent on the quality of this dose. Consequently, there is interest in characterizing the secondary radiation. Previously, we used the dual ionization chamber method to measure the separate absorbed dose from gamma‐rays and neutrons secondary to the proton beam1, relying on characterization of ionization chamber response in the unknown neutron spectrum from Monte Carlo simulation. We developed a procedure to use Shieldwerx activation foils, with neutron activation energies ranging from 0.025 eV to 13.5 MeV, to measure the neutron energy spectrum from double scattering (DS) and pencil beam scanning (PBS) protons outside of the treatment volume in a water tank. The activated foils are transferred to a NaI well chamber for gamma‐ray spectroscopy and activity measurement. Since PBS treats in layers, the switching time between layers is used to correct for the decay of the activated foils and the relative dose per layer is assumed to be proportional to the neutron fluence per layer. MATLAB code was developed to incorporate the layer delivery and switching time into a calculation of foil activity, which is then used to determine the neutron energy fluence from tabulated foil activation energy thresholds.1. Diffenderfer et. al., Med. Phys., 38(11) 2011.
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 tumors

Methods:

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.
SU‐F‐T‐185: Study of the Robustness of a Proton Arc Technique Based On PBS Beams
Authors: Wang Z , Zheng Y
Published: July 2016

Purpose:

One potential technique to realize proton arc is through using PBS beams from many directions to form overlaid Bragg peak (OBP) spots and placing these OBP spots throughout the target volume to achieve desired dose distribution. In this study, we analyzed the robustness of this proton arc technique.

Methods:

We used a cylindrical water phantom of 20 cm in radius in our robustness analysis. To study the range uncertainty effect, we changed the density of the phantom by ±3%. To study the setup uncertainty effect, we shifted the phantom by 3 & 5 mm. We also combined the range and setup uncertainties (3mm/±3%). For each test plan, we performed dose calculation for the nominal and 6 disturbed scenarios. Two test plans were used, one with single OBP spot and the other consisting of 121 OBP spots covering a 10×10cm2 area. We compared the dose profiles between the nominal and disturbed scenarios to estimate the impact of the uncertainties. Dose calculation was performed with Gate/GEANT based Monte Carlo software in cloud computing environment.

Results:

For each of the 7 scenarios, we simulated 100k & 10M events for plans consisting of single OBP spot and 121 OBP spots respectively. For single OBP spot, the setup uncertainty had minimum impact on the spot's dose profile while range uncertainty had significant impact on the dose profile. For plan consisting of 121 OBP spots, similar effect was observed but the extent of disturbance was much less compared to single OBP spot.

Conclusion:

For PBS arc technique, range uncertainty has significantly more impact than setup uncertainty. Although single OBP spot can be severely disturbed by the range uncertainty, the overall effect is much less when a large number of OBP spots are used. Robustness optimization for PBS arc technique should consider range uncertainty with priority.
SU‐F‐T‐190: Homogeneity Study of Proton and Heavy Ion Scanning Beams Based On Different Compositions of Spot Sizes (FWHM) and Grid Sizes
Authors: Zhao J , Hu W , Xing Y , Wu X , Li Y
Published: July 2016

Purpose:

Different particle scanning beam delivery systems have different delivery accuracies. This study was performed to determine, for our particle treatment system, an appropriate composition (n=FWHM/GS) of spot size(FWHM) and grid size (GS), which can provide homogenous delivered dose distributions for both proton and heavy ion scanning beam radiotherapy.

Methods:

We analyzed the delivery errors of our beam delivery system using log files from the treatment of 28 patients. We used a homemade program to simulate square fields for different n values with and without considering the delivery errors and analyzed the homogeneity. All spots were located on a rectilinear grid with equal spacing in the × and y directions. After that, we selected 7 energy levels for both proton and carbon ions. For each energy level, we made 6 square field plans with different n values (1, 1.5, 2, 2.5, 3, 3.5). Then we delivered those plans and used films to measure the homogeneity of each field.

Results:

For program simulation without delivery errors, when n≥1.1 the homogeneity can be within ±3%. For both proton and carbon program simulations with delivery errors and film measurements, the homogeneity can be within ±3% when n≥2.5.

Conclusion:

For our facility with system errors, the n≥2.5 is appropriate for maintaining homogeneity within ±3%.
SU‐F‐T‐192: Study of Robustness Analysis Method of Multiple Field Optimized IMPT Plans for Head & Neck Patients
Authors: Li Y , Wang X , Li H , Wang J , Zhu X , Li Y , Frank S , Zhang X
Published: July 2016

Purpose:

Proton therapy is more sensitive to uncertainties than photon treatments due to protons’ finite range depending on the tissue density. Worst case scenario (WCS) method originally proposed by Lomax has been adopted in our institute for robustness analysis of IMPT plans. This work demonstrates that WCS method is sufficient enough to take into account of the uncertainties which could be encountered during daily clinical treatment.

Methods:

A fast and approximate dose calculation method is developed to calculate the dose for the IMPT plan under different setup and range uncertainties. Effects of two factors, inversed square factor and range uncertainty, are explored. WCS robustness analysis method was evaluated using this fast dose calculation method. The worst‐case dose distribution was generated by shifting isocenter by 3 mm along x,y and z directions and modifying stopping power ratios by ±3.5%. 1000 randomly perturbed cases in proton range and x, yz directions were created and the corresponding dose distributions were calculated using this approximated method. DVH and dosimetric indexes of all 1000 perturbed cases were calculated and compared with the result using worst case scenario method.

Results:

The distributions of dosimetric indexes of 1000 perturbed cases were generated and compared with the results using worst case scenario. For D95 of CTVs, at least 97% of 1000 perturbed cases show higher values than the one of worst case scenario. For D5 of CTVs, at least 98% of perturbed cases have lower values than worst case scenario.

Conclusion:

By extensively calculating the dose distributions under random uncertainties, WCS method was verified to be reliable in evaluating the robustness level of MFO IMPT plans of H&N patients. The extensively sampling approach using fast approximated method could be used in evaluating the effects of different factors on the robustness level of IMPT plans in the future.
SU‐F‐T‐199: A New Strategy for Integrating Photon with Proton and Carbon Ion in the Treatment Planning
Authors: Chen Z , Wang J , Hu W
Published: July 2016

Purpose:

The aim of this study was to develop a viable strategy to integrate photon plan and proton/carbon ion plan based on deformable registration.

Methods:

Two prostate cancer patients were enrolled in this study. Each patient has 2 CTs, which were input in the Raystation radiotherapy treatment planning system (TPS). CT1 was deformed to the second CT2 using the Hybrid deformation method. The dice similarity coefficient (DSC) parameter was used to evaluate the difference between the actual structures (bladder, rectum and CTV) and the corresponding deformed structures on CT2. The prescription dose was 63.02GyE to CTV, which included 49.32GyE for CTV1 with carbon and boost 13.7Gy for CTV2 with photon. The carbon plan was made first in Syngo TPS (Syngo PT Planning system, version VB10. Siemens, Germany) on CT1 and transferred to Raystation TPS. Selected Isodoses (23.5Gy, 36.8Gy, 39.1Gy, 47.0Gy and 49.3Gy) of carbon plan were converted to contours and then deformed to CT2, which was used as normal tissues for photon plan optimization on CT2. The final plan was the combination of photon plan and the carbon deformation plan on the CT2. The plan from this strategy was compared with direct optimization of the photon plan on CT2 added some clinical endpoints from carbon plan on CT1.

Results:

The new strategy with deformable registration is tested and combined plans were successfully obtained for the 2 patients. This strategy obtained both integrated DVH and dose distribution information. For patient 1, the rectum V30, V60 and bladder V63 were 45.8, 10.3 and 9.7 for the combined plan with deformation and 48.1, 11.0 and 12.0 for the direct photon plan.

Conclusion:

The new strategy for combining photon and carbon/proton is feasible. However, the clinical accuracy is still need more evaluation.
SU‐F‐T‐200: Dosimetric Variation of Organs at Risk for Recurrent Nasopharyngeal Carcinoma (rNPC) Patients Treated by Carbon Ion Beams
Authors: Wang W , Sheng Y , Shahnazi K
Published: July 2016

Purpose:

Investigate the factors which affect the doses of organs at risk (OARs) for head and neck carbon ion therapy.

Methods:

Ten locally recurrent nasopharyngeal carcinoma cases with similar prescriptions were selected. All patients’ organs at risk (OARs) as well as CTVs were contoured by an experienced physician. Carbon ion treatment plans were created using a Syngo treatment planning system (Siemens, Germany). The CTVs were expanded to make optimized target volumes (OTVs) by considering treatment uncertainties and OAR protections. All plans were reviewed by this physician to be clinically acceptable. The OTV was expanded an additional 3mm to define the volume where beam spots could be put. A volume was also drawn 6 mm around the OTV to approximate the 50 % dose volume. The volumes where the OARs overlapped the OTV + 3 mm and OTV + 6 mm volumes, termed residual volumes, were then calculated.

Results:

The residual volumes within OTV + 3 mm were directly related to the OAR maximum dose. The percentage of the residual volume within the OTV + 6 mm with respect to the OAR volume was strongly related to the OAR mean doses. OAR mean doses also were affected by the beam setups. For example, if the OARs were in the beam entrance, the superior beams would sharply decrease the mean doses of the OARs hit by the lateral beams while increasing the mean doses of the OARs hit by the superior beam; the mean dose of the OARs which were hit by higher weight beams would be higher than the OARs hit by lower weight beams.

Conclusion:

Physicians should be cautious when contouring OARs, especially those close to CTVs and sensitive to large doses. Planners should set the OTV and beam parameters properly in order to save the OARs.
SU‐F‐T‐202: An Evaluation Method of Lifetime Attributable Risk for Comparing Between Proton Beam Therapy and Intensity Modulated X‐Ray Therapy for Pediatric Cancer Patients by Averaging Four Dose‐Response Models for Carcinoma Induction
Authors: Tamura M , Ito Y , Sakurai H , Mizumoto M , Kamizawa S , Murayama S , Yamashita H , Takao S , Suzuki R , Shirato H
Published: July 2016

Purpose:

To examine how much lifetime attributable risk (LAR) as an in silico surrogate marker of radiation‐induced secondary cancer would be lowered by using proton beam therapy (PBT) in place of intensity modulated x‐ray therapy (IMXT) in pediatric patients.

Methods:

From 242 pediatric patients with cancers who were treated with PBT, 26 patients were selected by random sampling after stratification into four categories: a) brain, head, and neck, b) thoracic, c) abdominal, and d) whole craniospinal (WCNS) irradiation. IMXT was re‐planned using the same computed tomography and region of interest. Using dose volume histogram (DVH) of PBT and IMXT, the LAR of Schneider et al. was calculated for the same patient. The published four dose‐response models for carcinoma induction: i) full model, ii) bell‐shaped model, iii) plateau model, and ix) linear model were tested for organs at risk. In the case that more than one dose‐response model was available, the LAR for this patient was calculated by averaging LAR for each dose‐response model.

Results:

Calculation of the LARs of PBT and IMXT based on DVH was feasible for all patients. The mean±standard deviation of the cumulative LAR difference between PBT and IMXT for the four categories was a) 0.77±0.44% (n=7, p=0.0037), b) 23.1±17.2%,(n=8, p=0.0067), c) 16.4±19.8% (n=8, p=0.0525), and d) 49.9±21.2% (n=3, p=0.0275, one tailed t‐test), respectively. The LAR was significantly lower by PBT than IMXT for the the brain, head, and neck region, thoracic region, and whole craniospinal irradiation.

Conclusion:

In pediatric patients who had undergone PBT, the LAR of PBT was significantly lower than the LAR of IMXT estimated by in silico modeling. This method was suggested to be useful as an in silico surrogate marker of secondary cancer induced by different radiotherapy techniques.

This research was supported by the Translational Research Network Program, JSPS KAKENHI Grant No. 15H04768 and the Global Institution for Collaborative Research and Education (GI‐CoRE), Hokkaido University, founded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
SU‐F‐T‐203: High Dose Definitive Proton Therapy with Integrated Boost to Hypoxic Subvolumes Determined by [18F]‐Fluoromisonidazole (FMISO) PET/CT for Patients with Recurrent Chordomas Using Intensity Modulated Proton Therapy (IMPT)
Authors: Yan S , Broussard G , De K , Bernstein Amorim , Wang Y
Published: July 2016

Purpose:

Recurrent chordomas are difficult to control locally. This dosimetric study investigates the feasibility of dose escalation to hypoxic regions, visualized on FMISO‐PET, while respecting the dose constraints to the neighboring normal tissues/organs. We propose to deliver a higher dose to the areas of hypoxia (84.5Gy) using IMPT with the goal of improving local control.

Methods:

We currently have four patients with hypoxic subvolumes (HSV) greater than 10cc from the FMISO‐PET image. The HSV was delineated based on the standardized uptake values of greater than 1.4 times of the muscle mean. Gross tumor volume (GTV) was delineated using planning CT with the assistance of MRI fusion. The dose scheme is 50.4Gy RBE to CTV in 1.8Gy fractions, followed by an integrated boost of 27.0Gy RBE to GTV in 1.8Gy fractions and 34.5Gy RBE to HSV in 2.3Gy fractions. IMPT integrated boost plans were optimized with multi‐criteria optimization (MCO). Posterior‐anterior beam angles were used for these plans. We also propose using two posterior oblique fields to boost HSV to spare the skin folding. A medium spot size with 8mm to 15 mm (σ) in air at isocenter with energies from 220 MeV down to 90 MeV was used. Aperture was used for the medium spot size. A small spot size of 2.5 mm to 4.5 mm (σ) in air at isocenter with energies from 240 MeV down to 70 MeV was also proposed. Target coverage and dose to OARs were evaluated.

Results:

For the sacral chordoma patient that has been planned, the target homogeneity index is 3.2% for HSV, 55.9% for CTV and 11.9% for GTV. The max dose is 77GyRBE to rectum, 86.2GyRBE to sacral nerves and 73.9GyRBE to cauda equina.

Conclusion:

IMPT with integrated high dose boost to HSV determined from FMISO PET image is feasible. OAR dose constraints were met.
SU‐F‐T‐205: Effectiveness of Robust Treatment Planning to Account for Inter‐ Fractional Variation in Intensity Modulated Proton Therapy for Head Neck Cancer
Authors: Li X , Zhang J , Qin A , Liang J , Zhou J , Yan D , Chen P , Krauss D , Ding X
Published: July 2016

Purpose:

To evaluate the potential benefits of robust optimization in intensity modulated proton therapy(IMPT) treatment planning to account for inter‐fractional variation for Head Neck Cancer(HNC).

Methods:

One patient with bilateral HNC previous treated at our institution was used in this study. Ten daily CBCTs were selected. The CT numbers of the CBCTs were corrected by mapping the CT numbers from simulation CT via Deformable Image Registration. The planning target volumes(PTVs) were defined by a 3mm expansion from clinical target volumes(CTVs). The prescription was 70Gy, 54Gy to CTV1, CTV2, and PTV1, PTV2 for robust optimized(RO) and conventionally optimized(CO) plans respectively. Both techniques were generated by RayStation with the same beam angles: two anterior oblique and two posterior oblique angles. The similar dose constraints were used to achieve 99% of CTV1 received 100% prescription dose while kept the hotspots less than 110% of the prescription. In order to evaluate the dosimetric result through the course of treatment, the contours were deformed from simulation CT to daily CBCTs, modified, and approved by a radiation oncologist. The initial plan on the simulation CT was re‐replayed on the daily CBCTs followed the bony alignment. The target coverage was evaluated using the daily doses and the cumulative dose.

Results:

Eight of 10 daily deliveries with using RO plan achieved at least 95% prescription dose to CTV1 and CTV2, while still kept maximum hotspot less than 112% of prescription compared with only one of 10 for the CO plan to achieve the same standards. For the cumulative doses, the target coverage for both RO and CO plans was quite similar, which was due to the compensation of cold and hot spots.

Conclusion:

Robust optimization can be effectively applied to compensate for target dose deficit caused by inter‐fractional target geometric variation in IMPT treatment planning.
SU‐F‐T‐207: Does the Greater Flexibility of Pencil Beam Scanning Reduce the Need for a Proton Gantry?
Authors: Yan S , Depauw N , Flanz J , Adams J , Gorissen BL , Shih H , Bortfeld T , Lu H
Published: July 2016

Purpose:

Gantry‐less proton treatment facility could lower the capital cost of proton therapy. This study investigates the dosimetric feasibility of using only coplanar pencil beam scanning (PBS) beams for those patients who had beam angles that would not have been deliverable without the gantry. Those coplanar beams are implemented on gantry‐less horizontal beam‐line with patients in sitting or standing positions.

Methods:

We have selected ten patients (seven head‐and‐neck, one thoracic, one abdominal and one pelvic case) with clinically delivered double scattering (DS) or PBS treatment plans with beam angles that were challenging to achieve without a gantry. After removing these beams angles, PBS plans were optimized for gantry‐less intensity modulated proton therapy (IMPT) or single field optimization (SFO) with multi‐criteria optimization (MCO). For head‐and‐neck patients who were treated by DS, we generated PBS plans with non‐coplanar beams for comparison. Dose‐volume‐histograms (DVHs), target homogeneity index (HI), mean dose, D_2 and D_98 were reported. Robustness analysis was performed with ±2.5 mm setup errors and ±3.5% range uncertainties for three head‐and‐neck patients.

Results:

PBS‐gantry‐less plans provided more homogenous target coverage and significant improvements on organs‐at‐risk (OARs) sparing, compared to passive scattering treatments with a gantry. The PBS gantry‐less treatments reduced the HI for target coverage by 1.3% to 47.2%, except for a suprasellar patient and a liver patient. The PBS‐gantry‐less plans reduced the D_mean of OARs by 3.6% to 67.4%. The PBS‐gantry plans had similar target coverage and only marginal improvements on OAR sparing as compared to the PBS‐gantry‐less plans. These two PBS plans also had similar robustness relative to range uncertainties and setup errors.

Conclusion:

The gantry‐less plans have with less mean dose to OARs and more homogeneous target coverage. Although the PBS‐gantry plans have slightly improved target coverage and OARs sparing, the overall benefit of having a gantry to provide non‐coplanar beams is debatable.
SU‐F‐T‐210: The Variable Virtual Source‐To‐Axis Distance Effect On A Compact Proton Pencil Beam Scanning System
Authors: Zhang J , Li X , Ding X
Published: July 2016

Purpose:

We investigate the spot characteristic and dose profiles properties from a compact gantry proton therapy system. This compact design features a dedicated pencil beam scanning nozzle with the scanning magnet located upstream of the final 60 degree bending magnet. Due to the unique beam line design, uncertainty has been raised in the virtual source‐to‐axis distance (SAD). We investigate its potential clinical impact through measurements and simulation.

Methods:

A scintillator camera based detector was used to measure spot characteristics and position accuracy. An ion chamber array device was used to measure planar dose profile. Dose profile in‐air simulation was performed using in‐house built MATLAB program based on additional spot parameters directly from measurements. Spot characteristics such as position and in‐air sigma values were used to general simulated 2D elliptical Gaussian spots. The virtual SAD distance changes in the longitudinal direction were also simulated. Planar dose profiles were generated by summation of simulated spots at the isocenter, 15 cm above the isocenter, and 15 cm below the isocenter for evaluation of potential clinical dosimetric impact.

Results:

We found that the virtual SAD varies depending on the spot location on the longitudinal axis. Measurements have shown that the variable SAD changes from 7 to 12 meters from one end to the other end of the treatment field in the longitudinal direction. The simulation shows that the planer dose profiles differences between the fixed SAD and variable SAD are within 3% from the isocenter profile and the lateral penumbras are within 1 mm difference.

Conclusion:

Our measurements and simulations show that there are minimum effects on the spot characteristics and dose profiles for this up‐stream scanning compact system proton system. Further treatment planning study is needed with the variable virtual SAD accounted for in the planning system to show minimum dosimetric impact.
SU‐F‐T‐212: A Comparison of Treatment Strategies for Intracranial Stereotactic Radiosurgery
Authors: Lamberton T , Slater J , Wroe A
Published: July 2016

Purpose:

Stereotactic radiosurgery is an effective and noninvasive treatment for intracranial lesions that uses highly focused radiation beams in a single treatment fraction. The purpose of this study is to investigate the dosimetric differences between the treatment brain metastasis with a proton beam vs. intensity modulated radiation therapy (IMRT).

Methods:

Ten separate brain metastasis targets where chosen and treatment plans were created for each, using three different strategies: custom proton beam shaping devices, standardized proton beam shaping devices, and IMRT. Each plan was required to satisfy set parameters for providing adequate coverage and minimizing risk to adjacent tissues. The effectiveness of each plan was calculated by comparing the homogeneity index, conformity index, and V12 for each target using a paired one tailed T‐test (α=0.05). Specific comparison of the conformity indices was also made using a subcategory containing targets with volume>1cc.

Results:

There was no significant difference between the homogeneity indices of the three plans (p>0.05), showing that each plan has the capability of adequately covering the targets. There was a statistically significant difference (p<0.01) between the conformity indices of the custom and the standard proton plan, as with the custom proton and IMRT (p<0.01), with custom proton showing stronger conformity to the target in both cases. There was also a statistical difference between the V12 of all three plans (Custom v. Standardized: p=0.02, Custom v. IMRT: p<0.01, Standardized v. IMRT: p<0.01) with custom proton supplying the lowest dose to surrounding tissues. For large targets (volume>1cc) there was no statistical difference between the proton plans and the IMRT treatment for the conformity index.

Conclusion:

A custom proton plan is the recommended treatment explored in this study as it is the most reliable way of effectively treating the target while sparing the maximum amount of normal tissue.
SU‐F‐T‐220: Validation of Hounsfield Unit‐To‐Stopping Power Ratio Calibration Used for Dose Calculation in Proton Radiotherapy
Authors: Polf J , Chung H , Langen K
Published: July 2016

Purpose:

To validate the stoichiometric calibration of the Hounsfield Unit (HU) to Stopping Power Ratio (SPR) calibration used to commission a commercial treatment planning system (TPS) for proton radiotherapy dose calculation. Methods and Materials: The water equivalent thickness (WET) of several individual pig tissues (lung, fat, muscle, liver, intestine, rib, femur), mixed tissue samples (muscle/rib, ice/femur, rib/air cavity/muscle), and an intact pig head were measured with a multi‐layer ionization chamber (MLIC). A CT scan of each sample was obtained and imported into a commercial TPS. The WET calculated by the TPS for each tissue sample was compared to the measured WET value to determine the accuracy of the HU‐to‐SPR calibration curve used by the TPS to calculate dose.

Results:

The WET values calculated by the TPS showed good agreement (< 2.0%) with the measured values for bone and all soft tissues except fat (3.1% difference). For the mixed tissue samples and the intact pig head measurements, the difference in the TPS and measured WET values all agreed to within 3.5%. In addition, SPR values were calculated from the measured WET of each tissue, and compared to SPR values of reference tissues from ICRU 46 used to generate the HU‐to‐SPR calibration for the TPS.

Conclusion:

For clinical scenarios where the beam passes through multiple tissue types and its path is dominated by soft tissues, we believe using an uncertainty of 3.5% of the planned beam range is acceptable to account for uncertainties in the TPS WET determination.