bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐520: Investigation of the Impact of Respiratory Motion On Spine SAbR Dose Distributions
Authors: Foster R , Ding C , Jiang S 
Published: June 2015

PurposeSpine SRS/SAbR treatment plans typically require very steep dose gradients to meet spinal cord constraints and it is crucial that the dose distribution be accurate. However, these plans are typically calculated on helical free‐breathing CT scans, which often contain motion artifacts. While the spine itself doesn't exhibit very much intra‐fraction motion, tissues around the spine, particularly the liver, do move with respiration. We investigated the dosimetric effect of liver motion on dose distributions calculated on helical free‐breathing CT scans for spine SAbR delivered to the T and L spine.MethodsWe took 5 spine SAbR plans and used density overrides to simulate an average reconstruction CT image set, which would more closely represent the patient anatomy during treatment. The value used for the density override was 0.66 g/cc. All patients were planned using our standard beam arrangement, which consists of 13 coplanar step and shoot IMRT beams. The original plan was recalculated with the same MU on the “average” scan and target coverage and spinal cord dose were compared to the original plan.ResultsThe average changes in minimum PTV dose, PTV coverage, max cord dose and volume of cord receiving 10 Gy were 0.6%, 0.8%, 0.3% and 4.4% (0.012 cc), respectively.ConclusionSAbR spine plans are surprisingly robust relative to surrounding organ motion due to respiration. Motion artifacts in helical planning CT scans do not cause clinically significant differences when these plans are re‐calculated on pseudo‐average CT reconstructions. This is likely due to the beam arrangement used because only three beams pass through the liver and only one beam passes completely through the density override. The effect of the respiratory motion on VMAT plans for spine SAbR is being evaluated.
SU‐E‐T‐521: Investigation of the Uncertainties Involved in Secondary Neutron/gamma Production in Geant4/MCNP6 Monte Carlo Codes for Proton Therapy Application
Authors: Mirzakhanian L , Giusti V , Enger S 
Published: June 2015

Purpose:A major concern in proton therapy is the production of secondary neutrons causing secondary cancers, especially in young adults and children. Most utilized Monte Carlo codes in proton therapy are Geant4 and MCNP. However, the default versions of Geant4 and MCNP6 do not have suitable cross sections or physical models to properly handle secondary particle production in proton energy ranges used for therapy. In this study, default versions of Geant4 and MCNP6 were modified to better handle production of secondaries by adding the TENDL‐2012 cross‐section library.Methods:In‐water proton depth‐dose was measured at the “The Svedberg Laboratory” in Uppsala (Sweden). The proton beam was mono‐energetic with mean energy of 178.25±0.2 MeV. The measurement set‐up was simulated by Geant4 version 10.00 (default and modified version) and MCNP6. Proton depth‐dose, primary and secondary particle fluence and neutron equivalent dose were calculated. In case of Geant4, the secondary particle fluence was filtered by all the physics processes to identify the main process responsible for the difference between the default and modified version.Results:The proton depth‐dose curves and primary proton fluence show a good agreement between both Geant4 versions and MCNP6. With respect to the modified version, default Geant4 underestimates the production of secondary neutrons while overestimates that of gammas. The “ProtonInElastic” process was identified as the main responsible process for the difference between the two versions. MCNP6 shows higher neutron production and lower gamma production than both Geant4 versions.Conclusion:Despite the good agreement on the proton depth dose curve and primary proton fluence, there is a significant discrepancy on secondary neutron production between MCNP6 and both versions of Geant4. Further studies are thus in order to find the possible cause of this discrepancy or more accurate cross‐sections/models to handle the nuclear interactions of protons with energy ranges used for therapy.NSERC‐CRSNG’ CREATE Medical Physics Research Training Network compute calcul CANADA; McGill University health center research institute the fast foundation; LM acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering; Research Council Grant number 432290
SU‐E‐T‐533: LET Dependence Correction of Radiochromic Films for Application in Low Energy Proton Irradiation
Authors: Reinhardt S , Wuerl M , Greubel C , Wilkens J , Hillbrand M , Mairani A , Assmann W , Parodi K 
Published: June 2015

Purpose:Many cell irradiation experiments with low‐energy laser‐driven ions rely on radiochromic films (RCF), because of their dose‐rate independent response and superior spatial resolution. RCF dosimetry in low‐energy ion beams requires a correction of the LET dependent film response. The relative efficiency (RE), the ratio of photon to proton dose that yields the same film darkening, is a measure for the film's LET dependence. A direct way of RE determination is RCF irradiation with low‐energy mono‐energetic protons and hence, well‐defined LET. However, RE is usually determined using high energy proton depth dose measurements where RE corrections require knowledge of the average LET in each depth, which can be either track (tLET) or dose (dLET) averaged. The appropriate LET concept has to be applied to allow a proper film response correction.Methods:Radiochromic EBT2 and EBT3 films were irradiated in clinical photon and proton beams. For each depth of the 200 MeV proton depth dose curve, tLET and dLET were calculated by special user routines from the Monte Carlo code FLUKA. Additional irradiations with mono‐energetic low energy protons (4–20 MeV) serve as reference for the RE determination.Results:The difference of dLET and tLET increases with depth, with the dLET being almost twice as large as the tLET for the maximum depth. The comparison with mono‐energetic measurements shows a good agreement of the RE for the dLET concept, while a considerably steeper drop in RE is observed when applying the tLET.Conclusion:RCF can be used as reference dosimeter for biomedical experiments with low‐energy proton beams if appropriate LET corrections are applied. When using depth dose measurements from clinical proton accelerators for these corrections, the concept of dLET has to be applied.Acknowledgement:This work was funded by the DFG Cluster of Excellence ‘Munich‐Centre for Advanced Photonics’ (MAP).This work was funded by the DFG Cluster of Excellence Munich‐Centre for Advanced Photonics (MAP).
SU‐E‐T‐539: Maximum Energy of Helium and Carbon Ions Clinically Needed for Spine, Lung, Prostate and Pancreas Cancer
Authors: Pompos A , Choy H , Jia X , Jiang S , Timmerman R 
Published: June 2015

Purpose:Maximum available kinetic energy of accelerated heavy ions is a critical parameter to consider during the establishment of a heavy ion therapy center. It dictates the maximum range in tissue and determines the size and cost of ion gantry. We have started planning our heavy ion therapy center and we report on the needed ion range.Methods:We analyzed 50 of random SBRT‐spine, SBRT‐ lung, prostate and pancreatic cancer patients from our photon clinic. In the isocentric axial CT cut we recorded the maximum water equivalent depth (WED4Field) of PTV's most distal edge in four cardinal directions and also in a beam direction that required the largest penetration, WEDGantry. These depths were then used to calculate the percentage of our patients we would be able to treat as a function of available maximum carbon and helium beam energy. Based on the Anterior‐Posterior WED for lung patients and the maximum available ion energy we estimated the largest possible non‐coplanar beam entry angle φ (deviation from vertical) in the isocentric vertical sagittal plane.Results:We found that if 430MeV/u C‐12, equivalently 220MeV/u He‐4, beams are available, more than 96% (98%) of all patients can be treated without any gantry restrictions (in cardinals angles only) respectively. If the energy is reduced to 400MeV/u C‐12, equivalently 205MeV/u He‐4, the above fractions reduce to 80% (87%) for prostate and 88% (97%) for other sites. This 7% energy decrease translates to almost 5% gantry size and cost decrease for both ions. These energy limits in combination with the WED in the AP direction for lung patients resulted in average non‐coplanar angles of φ430MeV/u = 68°±8° and φ400MeV/u = 65°±10° if nozzle clearance permits them.Conclusion:We found that the two worldwide most common maximum carbon beam energies will treat above 80% of all our patients.
SU‐E‐T‐543: Measurement of Neutron Activation From Different High Energy Varian Linear Accelerators
Authors: Thatcher T , Meigooni A Soleimani , Madsen S , Sudowe R 
Published: June 2015

Purpose:Linear accelerators producing photons above 10 MeV may induce photonuclear reactions in high Z components of the accelerator. These liberated neutrons can then activate the structural components of the accelerator and other materials in the beam path through neutron capture reactions. The induced activity within the accelerator may contribute to additional dose to both patients and personnel. This project seeks to determine the total activity and activity per activated isotope following irradiation in different Varian accelerators at energies above 10 MeV.Methods:A Varian 21IX accelerator was used to irradiate a 30 cm × 30 cm × 20 cm solid water phantom with 15 MV x‐rays. The phantom was placed at an SSD of 100 cm and at the center of a 20 cm × 20 cm field. Activation induced gamma spectra were acquired over a 5 minute interval after 1 and 15 minutes from completion of the irradiation. All measurements were made using a CANBERRA Falcon 5000 Portable HPGe detector. The majority of measurements were made in scattering geometry with the detector situated at 90° to the incident beam, 30 cm from the side of the phantom and approximately 10 cm from the top. A 5 minute background count was acquired and automatically subtracted from all subsequent measurements. Photon spectra were acquired for both open and MLC fields.Results:Based on spectral signatures, nuclides have been identified and their activities calculated for both open and MLC fields. Preliminary analyses suggest that activities from the activation products in the microcurie range.Conclusion:Activation isotopes have been identified and their relative activities determined. These activities are only gross estimates since efficiencies have not been determined for this source‐detector geometry. Current efforts are focused on accurate determination of detector efficiencies using Monte Carlo calculations.
SU‐E‐T‐544: Microscopic Dose Enhancement of Gold Nanoparticles in Water for Proton Therapy: A Simulation Study
Authors: Newpower M , Ahmad S , Chen Y 
Published: June 2015

Purpose:To quantify the microscopic dose and linear energy transfer (LET) enhancement of gold nanoparticles (GNPs) in water for proton therapy.Methods:The GEANT4 toolkit (version 10) with low energy electromagnetic classes was used to create a series of simulations where three radii (r=5, 20, 100 nm) of gold nanoparticles (GNPs) were irradiated with 5 × 106 80 MeV protons. A cubic detector (10 × 10 × 10 um, divided in 25 × 25 × 25 voxels) were placed in a water phantom where the GNP rests in the center. The size of incident proton beam was set to be same as the GNPs and perpendicularly aiming to the target. Dose deposited to each voxel were recorded to calculate the overall deposited dose and the dose‐averaged LET. The emitted secondary electron spectra were also collected in a spherical customized scorer (radius = 150 nm).Results:The average dose from a single GNP in a cubic water phantom was increased by 0.12 %, 1.12% and 2.3% and the mean dose‐averaged LET was increased by 5.87% and 27.67% and 0.31% for GNP radius of 5 nm, 20 nm and 100 nm, respectively.Conclusion:The dose enhancement effect from the presence of a single GNP was qualified in a water phantom. A significant increase in the mean dose‐averaged LET was found for 20 nm GNP.
SU‐E‐T‐545: MLC Distance Travelled as a Predictor for Motor Failure
Authors: Stathakis S , Defoor D , Linden P , Kirby N , Mavroidis P , Papanikolaou N 
Published: June 2015

Purpose:To study the frequency of Multi‐Leaf Collimator (MLC) leaf failures, investigate methods to predict them and reduce linac downtime.Methods:A Varian HD120 MLC was used in our study. The hyperterminal MLC errors logged from 06/2012 to 12/2014 were collected. Along with the hyperterminal errors, the MLC motor changes and all other MLC interventions by the linear accelerator engineer were recorded. The MLC dynalog files were also recorded on a daily basis for each treatment and during linac QA. The dynalog files were analyzed to calculate root mean square errors (RMS) and cumulative MLC travel distance per motor. An in‐house MatLab code was used to analyze all dynalog files, record RMS errors and calculate the distance each MLC traveled per day.Results:A total of 269 interventions were recorded over a period of 18 months. Of these, 146 included MLC motor leaf change, 39 T‐nut replacements, and 84 MLC cleaning sessions. Leaves close to the middle of each side required the most maintenance. In the A bank, leaves A27 to A40 recorded 73% of all interventions, while the same leaves in the B bank counted for 52% of the interventions. On average, leaves in the middle of the bank had their motors changed approximately every 1500m of travel. Finally, it was found that the number of RMS errors increased prior to an MLC motor change.Conclusion:An MLC dynalog file analysis software was developed that can be used to log daily MLC usage. Our eighteen‐month data analysis showed that there is a correlation between the distance an MLC travels, the RMS and the life of the MLC motor. We plan to use this tool to predict MLC motor failures and with proper and timely intervention, reduce the downtime of the linac during clinical hours.
SU‐E‐T‐550: Modulation Index for VMAT
Authors: Park J , Park S , Kim J , Kim H , Kim J , Carlson J , Ye S 
Published: June 2015

Purpose:To present modulation indices (MIs) for volumetric modulated arc therapy (VMAT).Methods:A total of 40 VMAT plans were retrospectively selected. To investigate the delivery accuracy of each VMAT plan, gamma passing rates, differences in modulating parameters between plans and log files, and differences between the original plans and the plans reconstructed with the log files were acquired. A modulation index (MIt) was designed by multiplications of the weighted quantifications of MLC speeds, MLC accelerations, gantry accelerations and dose‐rate variations. Textural features including angular second moment, inverse difference moment, contrast, variance, correlation and entropy were calculated from the fluences of each VMAT plan. To test the performance of suggested MIs, Spearman's rank correlation coefficients (r) with the plan delivery accuracy were calculated. Conventional modulation indices for VMAT including the modulation complexity score for VMAT (MCSv), leaf travel modulation complexity score (LTMCS) and MI by Li & Xing were calculated, and their correlations were also analyzed in the same way.Results:The r values of contrast (particular displacement distance, d = 1), variance (d = 1), MIt, MCSv, LTMCS and MI by Li&Xing to the local gamma passing rates with 2%/2 mm were 0.547 (p < 0.001), 0.519 (p < 0.001), −0.658 (p < 0.001), 0.186 (p = 0.251), 0.312 (p = 0.05) and −0.455 (p = 0.003), respectively. The r values of those to the MLC errors were −0.863, −0.828, 0.917, −0.635, − 0.857 and 0.795, respectively (p < 0.001). For dose‐volumetric parameters, MIt showed higher statistically significant correlations than did the conventional modulation indices.Conclusion:The MIt, contrast (d = 1) and variance (d = 1) showed good performance to predict the VMAT delivery accuracy showing higher correlations to the results of various types of verification methods for VMAT.This work was in part supported by the National Research Foundation of Korea (NRF) grant (no. 490‐20140029 and no. 490‐20130047) funded by the Korea government.
SU‐E‐T‐552: Monte Carlo Calculation of Correction Factors for a Free‐Air Ionization Chamber in Support of a National Air‐Kerma Standard for Electronic Brachytherapy
Authors: Mille M , Bergstrom P 
Published: June 2015

Purpose:To use Monte Carlo radiation transport methods to calculate correction factors for a free‐air ionization chamber in support of a national air‐kerma standard for low‐energy, miniature x‐ray sources used for electronic brachytherapy (eBx).Methods:The NIST is establishing a calibration service for well‐type ionization chambers used to characterize the strength of eBx sources prior to clinical use. The calibration approach involves establishing the well‐chamber's response to an eBx source whose air‐kerma rate at a 50 cm distance is determined through a primary measurement performed using the Lamperti free‐air ionization chamber. However, the free‐air chamber measurements of charge or current can only be related to the reference air‐kerma standard after applying several corrections, some of which are best determined via Monte Carlo simulation. To this end, a detailed geometric model of the Lamperti chamber was developed in the EGSnrc code based on the engineering drawings of the instrument. The egs_fac user code in EGSnrc was then used to calculate energy‐dependent correction factors which account for missing or undesired ionization arising from effects such as: (1) attenuation and scatter of the x‐rays in air; (2) primary electrons escaping the charge collection region; (3) lack of charged particle equilibrium; (4) atomic fluorescence and bremsstrahlung radiation.Results:Energy‐dependent correction factors were calculated assuming a monoenergetic point source with the photon energy ranging from 2 keV to 60 keV in 2 keV increments. Sufficient photon histories were simulated so that the Monte Carlo statistical uncertainty of the correction factors was less than 0.01%. The correction factors for a specific eBx source will be determined by integrating these tabulated results over its measured x‐ray spectrum.Conclusion:The correction factors calculated in this work are important for establishing a national standard for eBx which will help ensure that dose is accurately and consistently delivered to patients.
SU‐E‐T‐554: Monte Carlo Calculation of Source Terms and Attenuation Lengths for Neutrons Produced by 50–200 MeV Protons On Brass
Authors: Ramos‐Mendez J , Paganetti H , Faddegon B 
Published: June 2015

Purpose:We used TOPAS (TOPAS wraps and extends Geant4 for medical physicists) to compare Geant4 physics models with published data for neutron shielding calculations. Subsequently, we calculated the source terms and attenuation lengths (shielding data) of the total ambient dose equivalent (TADE) in concrete for neutrons produced by protons in brass.Methods:Stage1: The Bertini and Binary nuclear models available in Geant4 were compared with published attenuation at depth of the TADE in concrete and iron. Stage2: Shielding data of the TADE in concrete was calculated for 50– 200 MeV proton beams on brass. Stage3: Shielding data from Stage2 was extrapolated for 235 MeV proton beams. This data was used in a point‐line‐source analytical model to calculate the ambient dose per unit therapeutic dose at two locations inside one treatment room at the Francis H Burr Proton Therapy Center. Finally, we compared these results with experimental data and full TOPAS simulations.Results:At larger angles (∼130o) the TADE in concrete calculated with the Bertini model was about 9 times larger than that calculated with the Binary model. The attenuation length in concrete calculated with the Binary model agreed with published data within 7%±0.4% (statistical uncertainty) for the deepest regions and 5%±0.1% for shallower regions. For iron the agreement was within 3%±0.1%. The ambient dose per therapeutic dose calculated with the Binary model, relative to the experimental data, was a ratio of 0.93±0.16 and 1.23±0.24 for two locations. The analytical model overestimated the dose by four orders of magnitude. These differences are attributed to the complexity of the geometry.Conclusion:The Binary and Bertini models gave comparable results, with the Binary model giving the best agreement with published data at large angle. Shielding data we calculated using the Binary model is useful for fast shielding calculations with other analytical models.This work was supported by National Cancer Institute Grant R01CA140735
SU‐E‐T‐560: Monte Carlo Simulation of the Neutron Radiation Field Around a Medical 18 MV Linac
Authors: Horst F , Czarnecki D , Zink K 
Published: June 2015

Purpose:Today the majority of radiation therapy treatments are performed at medical electron linear accelerators (linacs). The accelerated electrons are used for the generation of bremsstrahlung photons. The use of higher electron respectively photon energies has some advantages over lower energies such as the longer dose build‐up. However photons with energies higher than ∼7 MeV can additionally to the interaction with bound electrons undergo inelastic reactions with nuclei. These photonuclear reactions lead to the emission of fast neutrons which contaminate the primary photon field. The neutrons might penetrate through the collimators and deliver out‐of‐field dose to the patient. Furthermore the materials inside the linac head as well as the air inside the treatment room get activated which might deliver dose to the medical employees even when the linac is not in operation. A detailed knowledge of these effects is essential for adequate radiation protection of the employees and an optimal patient treatment.Methods:It is a common method to study the radiation fields of such linacs by means of Monte Carlo simulations. For the investigation of the effects caused by photonuclear reactions a typical linac in high energy mode (Varian Clinac 18 MV‐X) as well as the surrounding bunker were modelled and simulated using the Monte Carlo code FLUKA which includes extensive nuclear reaction and neutron transport models additional to electron‐photon transport as well as capabilities for a detailed study of effective dose distributions and activation yields.Results:Neutron spectra as well as neutron effective dose distributions within the bunker were obtained, reaching up to some mSv/Gy in the patient's plane. The results are normalized per Gy in the depth dose maximum at 10×10 cm2 field size. Therefore an absolute interpretation is possible.Conclusion:The obtained data gives a better understanding of the photonuclear reaction caused effects.