bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐408: Validation of a Novel Dose Calculation Approach for Heterogeneous Voxelized Phantoms in a Parallel Computation Environment Using Electron Dose Kernels for Radiotherapy
Authors: Huang M , Sjoden G , Li J , Al‐Basheer A , Bolch W
Published: August 2010

Purpose Here we present a rapid whole body dose estimation approach applied to a clinical water phantom and whole body CT‐voxelized phantom, using electron dose kernels coupled with deterministic photon transport. This method yields fast, accurate whole body doses. Method and Materials A novel dose calculation methodology called EDK‐SN, or “Electron Dose Kernel‐Discrete Ordinates” rapidly estimates organ doses in a voxelized human phantom, accounts for in‐ and out‐of‐field doses using external photon beam therapy. We begin by solving the complete photon transport problem using parallel computing with the 3‐D discrete ordinates (SN) photon transport code PENTRAN. We then project pre‐computed (via Monte Carlo) voxel‐based Electron Dose Kernels (EDKs), mapping them to surrounding voxels via quaternion rotation, scaled by the magnitude of photon fluence from the SN calculation. An 8 MV flat‐weighted beam is incident on an 11×11×11 cm3 water phantom, and on a 15 year old human phantom, down‐sampled to 1×1×1 cm3 (60×27×167 voxels); a 6 MV Philips Elekta Linac photon spectrum has also been simulated. The percent depth dose was compared to clinical CC04 chamber measurement results; comparison of doses using the EDK‐Sn method and clinical treatment planning system (in field dose) will also be presented. Results The EDK‐SN technique has demonstrated independent agreement with Monte Carlo photon‐electron transport calculations for whole body dose. The EDK‐SN method yields a speedup of ∼8 (30 minutes versus 4+ hours) over the traditional parallel Monte Carlo, with <7% difference in different organs (smaller given stochastic uncertainties). The Monte Carlo simulated percent depth dose and clinical chamber PDD measurement agree within 10% among different field sizes. Conclusion The EDK‐SN method for high energy photon external beam dose calculations has been validated based on clinical external therapy beam calculations. This method will help to determine both in‐field and out‐of‐field radiation dose for radiotherapy.
SU‐GG‐T‐409: Comparison of Proton MLC with Non‐Divergent Brass and Tungsten Apertures
Authors: Kirk M , Ainsley C , McDonough J
Published: August 2010

Purpose: To examine proton edge scattering effects from a tungsten MLC, specifically in comparison with proton edge effects using a non‐divergent brass aperture. Methods and Materials: The standard for proton therapy beam shaping is a custom‐cut, non‐divergent aperture with thickness ∼65mm. To make comparisons with tungsten MLC simulations, a Monte Carlo simulation model created with GEANT4 was run for non‐divergent apertures made of tungsten and brass at thicknesses of 65, 75, and 85 mm. Simulations with each type of aperture were run for IBA's proton double‐scattering options B1, B4, and B7 at 100 and 550 mm elevations with square field sizes of 15×15, 10×10, and 5×5 cm2 and aperture‐to‐phantom air gaps of 1 and 4 cm. MLC simulations were verified with beam profile measurements using the same treatment parameters. Results: Dose profiles of proton beams have horns similar to dose profiles with X‐ray beams, but they originate from protons scattering back into the field at the field edge. Using non‐divergent tungsten and brass apertures, the size of the horns on dose profiles at the entrance of the simulated water phantom were found to follow the same trends as the leaf edge fields of the MLC. The profiles from the tungsten MLC fields were compared with the best case thickness (65 mm) for brass and tungsten apertures. MLC profiles have horns only along the axis of leaf travel due to MLC design, while the non‐divergent apertures have equally large horns along both axes, as expected given the symmetry. Along the axis of leaf travel the horns resulting from edge scatter off of the MLC were approximately equal to or smaller than horns from edge scatter off of the non‐divergent apertures. Conclusions: Proton dose profiles using a tungsten MLC have no worse edge‐scattering effects than a non‐divergent brass aperture.
SU‐GG‐T‐410: Evaluation of Varian's AAA Algorithm by Monte Carlo Simulation for Lung Cancer SBRT
Authors: Jin L , Wang L , Fan J , Li J , Price R , Ma C
Published: August 2010

Purpose: This work investigates the accuracy of the Anisotropic Analytical Algorithm (AAA) of Eclipse treatment planning system for linac‐based lung cancer stereotactic body radiotherapy (SBRT) using well‐benchmarked Monte Carlo (MC) simulations. Method and Materials: Comparisons between AAA and Monte Carlo dose calculations were performed for both single‐beam dose distributions and four realistic clinical patient plans with planning target volume (PTV) ranging from 7.4 cc to 22.4 cc. Isodose distributions and dose profiles were compared for the single beam calculations while for the patient plans dose volume histograms (DVH) were also compared together with the doses received by the PTV and critical structures (lung, esophagus, spinal cord, left ventricle and carina). Results: Comparisons of dose profiles between the AAA and the MC calculations showed minor differences between the two algorithms at the interfaces between the lung and the tumor or other high density tissues (about 4.0% of the maximum dose/2mm along both the lateral and anterior‐posterior directions). The mean dose to the PTV calculated by the AAA for all four patients was lager than those calculated by MC simulations, but not larger than 2.5 % of the prescription dose. However, for the patient with the smallest PTV (7.4cc), the maximum PTV dose calculated by the AAA is 3.75% less than that calculated by MC. The mean dose differences between the two algorithms to critical structures are not significant, all less than 0.6% of the prescription dose. Conclusion: The AAA algorithm is superior to those simple algorithms that do not account for electron transport although it exhibits minor problems in dealing with tissue interfaces. For SBRT lung cancer planning, the AAA is adequate for the PTV with a better than 3% dose accuracy (possibly except for target volumes less than 10 cc) and even smaller uncertainties to critical structures.
SU‐GG‐T‐411: Monte‐Carlo‐Based Cavity Correction Factors for Ion Chambers in Clinical Electron Beams
Authors: Ono T , Araki F , Yoshiyama F
Published: August 2010

Purpose: To calculate the cavity correction factor, Pcav at various depths for cylindrical chambers and plane‐parallel chambers, NACP‐02 and ROOS, in high‐energy electron beams by means of the EGSnrc/Cavity code. Method and Materials: The chamber cavity was simulated in detail by the EGSnrc/Cavity code. Pcav was calculated at various depths which include a reference depth, dref, and a half‐value depth, R50, for 6, 9, 15, and 18 MeV electron beams. The effective point of the calculation was at a point shifted 0.5r upstream from the cavity center for cylindrical chambers and was the front face of the cavity for plane‐parallel chambers. Pcav for the cylindrical chamber cavities were calculated with combinations of the diameters of 2, 4, and 6 mm and the lengths of 5, 10, and 20 mm. The results were compared with the values recommended by TRS‐398 and other published data. Results: Pcav values increased as a function of a depth. Especially, the Pcav values at dref for cylindrical chambers were 4–10% higher than those at R50 in 6 MeV. Pcav values were lower with increasing the cavity diameter and decreasing the cavity length. This is because the lateral scattered electrons entering into the chamber cavity from the surrounding water increase. The effect is significant in lower‐energy beams. Similarly, the Pcav values are 0.993 at dref and 1.030 at R50 for NACP‐02 and 1.001 and 1.030 for ROOS in 6 MeV. Pcav for NACP‐02 varies depending on depths (electron mean energy). The variation in Pcav for ROOS values is smaller than NACP‐02 because its guard‐ring is larger. Conclusion: The calculated Pcav value was sufficiently different from TRS‐398 data. The Pcav values vary depending on electron mean energy and the chamber cavity size. For plan‐parallel chambers, the sufficient guard‐ring width needs to decrease the cavity correction.
SU‐GG‐T‐414: Directional Dependence of the Response of Plastic Scintillation Detectors in Photon Beams
Authors: Wang L , Klein D , Beddar S
Published: August 2010

Purpose: The plastic scintillation detector (PSD) is a promising dosimeter for in vivo dosimetry due to its high spatial resolution and excellent water equivalency. The arbitrary orientation of PSD, when placed inside a patient body, may affect its relative response. This study investigates the directional dependence of the response of PSD in photon beams by Monte Carlo simulations. Method and Materials: Two PSDs (BC‐400 and BCF‐12), each coupled to an optical fiber stem, are modeled. The directional dependences of the response of both PSDs in a water phantom are studied for a 6 MV spectral photon beam and a 300 keV mono‐energetic photon beam. Different optical fiber core materials (plastic, glass, and air) are used in the calculation model to study the influence of the optical fiber materials upon the directional dependence of the detector response. Results: For the majority of angles between the detector axis and the incident beam direction, the response of the PSDs is within 1∼2 % irrespective of the photon energy or the optical fiber material used. For the case when the optical fiber stem is pointing to the source, the PSDs with glass or air cored optical fibers show larger deviations (6 % for 6 MV beam and 15 % for 300 keV beam) while the response for the PSDs with plastic cored optical fibers is still within 2 %. Conclusion: If plastic is used for the fiber core, the directional dependence is not of concern at 2 % level in photon beams. If glass or air is used for the fiber core, the PSD response has a 6 % deviation or more when the optical fiber stem is pointing to the source, which is probable for in vivo applications as the orientation of the detector cannot be guaranteed. Supported by the NCI (1R01CA120198‐01A2)
SU‐GG‐T‐415: Automated Photon Monte Carlo Linear Accelerator Model for Calculating In‐Field and Out‐Of‐Field Dose
Authors: Randeniya S , Mirkovic D , Kry S , Titt U , Newhauser W , Howell R
Published: August 2010

Purpose: Monte Carlo methods have been used extensively to calculate radiation does to organs both in‐field and far‐field. However, particularly for out‐of‐field dose calculations, this process has relied on the very time consuming and potentially error‐prone manual conversion of radiation field parameters and CT datum to a Monte Carlo input format. The purpose of this study was to develop computational infrastructure to automate a Monte Carlo‐based dose calculation algorithm for a previously modeled and benchmarked Varian 2100 linear accelerator operating at 6 MV. This system would be suitable for in‐field and out‐of‐field calculations. Method and Materials: A computer program was written using a Digital Imaging and Communications Tool Kit (DCMTK) to extract patient position data and radiation field parameters from a photon radiation therapy (RT) file and, based on this data, set the MCNPX simulation geometry for the modeled linear accelerator. A shell script was written to automate extraction, writing MCNPX geometry input files and submission of simulations to a computer cluster. The accuracy of the automation process was tested by examining the accuracy of the in‐field dose from an eight‐field, intensity modulated radiotherapy plan. Each field corresponded to a different gantry angle and set of control points. For each field, simulated depth‐dose curves and cross‐filed dose profiles at isocenter were compared with dose profiles calculated from Varian treatment planning software (Eclipse). Results: In‐field dose profiles calculated from the automated system agreed within 4% to dose profiles calculated using the Eclipse. Statistical uncertainty of simulated in‐field dose profiles was at most 4%. Conclusion: The automated dose calculation system accurately extracted the complex treatment geometry parameters, and successfully incorporated them into the Monte Carlo framework. This process substantially reduces the time required, and potential for error, for conducting Monte Carlo simulations within or outside the treatment field.
SU‐GG‐T‐416: Validation of a Varian BrachyVision Calculation Model for a GammaMed Plus HDR Source and Evaluating Heterogeneity Effects for Four Clinical Cases Using EGSnrc Monte Carlo User Code
Authors: Bassalow R , Gong J
Published: August 2010

Purpose: Varian BrachyVision (BV) treatment planning system uses TG43 parameters derived from Monte Carlo modeling. Dose perturbation effects due to the presence of heterogeneities have been examined previously to verify Plato TPS using various MC codes. The purpose of this work was 1) to obtain an independent verification of the calculation model used by the BV treatment planning system for a GammaMed Plus source using EGSnrc Monte Carlo code, 2) to evaluate the heterogeneity effects for a sample of clinical cases planned for GammaMed Plus HDR cylinder and MammoSite. Method and Materials: Dose profiles and point dose calculations for three MammoSite cases with varying distance to the skin and lung, and a vaginal cylinder case were compared to MC simulations using EGSnrc dosxyznrc user code which allows for a 3D arbitrary geometry as well as to perform calculations using full planning CT data. In a previous work which used an EGSnrc dosrznrc code researchers performed 2D calculations due to cylindrical geometry constraints for that code. Results: Our Monte Carlo and BV calculations were in a good agreement for a test case of uniform medium. Dose reduction was observed inside the balloon due to the presence of higher‐Z contrast media and on the side of the tissue at the tissue ‐ air bubble interface and tissue‐lung interface. Dose in the lung was also elevated. These heterogeneity air perturbation effects however seem slightly more pronounced: 17.1% for BV vs previously reported 3.6% for the Plato system. Conclusion: These preliminary results demonstrate excellent agreement with the BrachyVision model in a uniform medium, but show rather pronounced dose perturbation effects in heterogeneous media. More investigation is needed to understand the higher scale of the heterogeneity perturbation effects.
SU‐GG‐T‐418: Comparing Computational Phantoms and Whole‐Body Patient CT Images for Secondary Cancer Risk Estimation
Authors: Taranenko V , Paganetti H , Juneja B , Bolch W
Published: August 2010

Purpose: To check the sensitivity of anatomy detailing on the quantification of second cancer risk in pediatric patients treated with passively scattered protons. Method and Materials: Clinical radiation treatment plans for medulloblastoma were analyzed and representative beams were selected for conversion to a Monte Carlo system for dose calculations in Geant4. Phase space files, separately for primary protons and treatment head generated neutrons, were generated at the exit of the beam‐shaping aperture using the detailed model of the MGH treatment nozzle for 4 circular fields: center of brain, superior‐, mid‐ and inferior‐spine; range (90‐90%) of 11 cm, modulation width of 5 cm, aperture diameters of 3 and 9 cm (higher and lower neutron contributions, respectively). Anonymized whole‐body patient CT data from pediatric patients treated with protons were incorporated into Geant4 simulation code. Three sets of age‐dependent pediatric whole body fully‐segmented phantoms developed at the University of Florida were incorporated as well: the UF‐B series, the new ICRP‐compliant series and a patient‐adjusted ‘hybrid’ phantom. To calculate organ equivalent doses, radiation weighting factors were used. Results for organ equivalent doses were compared between different anatomical representations. The number of particles generated in the phase space files varied 1.4–9 million. Results: The results on organ doses show a discrepancy of 40–70% for out‐of‐the‐field organs close to the beam, and up to a factor of five for organs further away. The latter is partially due poor statistics in dose scoring. Conclusion: Fully‐segmented whole body computational phantoms are indispensable for risk analysis where organ doses through the full patient body are needed but rarely available due to lack of CT or segmentation. The error of using voxelized and non‐stylized phantoms instead of patient specific anatomy is lower than in current risk models, hence they are suitable for estimating the organ doses.
SU‐GG‐T‐420: Electron Monte Carlo Dose Calculation in Eclipse for Elekta Linear Accelerators
Authors: Fix MK , Frei D , Volken W , Neuenschwander H , Born EJ , Manser P
Published: August 2010

Purpose: The macro Monte Carlo (MC) method as implemented in Eclipse (Varian Medical Systems), named eMC, is only released for Varian accelerators. This is due to limitations in accuracy if eMC is applied to Elekta machines. This work describes improvements made in eMC to achieve accurate dose calculations of electron beams for Elekta accelerators. Method and Materials: Several changes recently implemented in the original eMC algorithm for low electron beam energies of Varian linear accelerators have been applied for the modeling of Elekta machines. In order to make eMC available for Elekta machines, the second divergent photon and electron source in the beam model for Varian accelerators have to be replaced with a line source to model the head scatter radiation more accurately. With respect to the dose calculation algorithm, the transport of the secondary electron component has been improved including modifications in the database of the transport code. Calculated and measured dose distributions are compared for Elekta machines using electron energies of 6, 8, 9, 12 and 15 MeV and applicators ranging from 6×6 to 20×20 cm2. Results: Calculated and measured absolute depth dose curves agree generally within 1.5% or 1 mm at a source to surface distance (SSD) of 100 cm. For SSD = 110 cm the differences are usually within 2% or 2 mm. Calculated and measured absolute dose profiles at depths of dmax and in the photon tail generally agree to within 2%. Some dose values close to the field edge show slightly larger differences. Conclusion: The results of the dose comparisons using the newly developed version of eMC suggest that this new eMC is now suitable to predict dose distributions for Elekta linear accelerators within sufficient accuracy. Conflict of Interest: This work was supported by Varian Medical Systems.
SU‐GG‐T‐423: Tissue Composition Effect in Proton Dose Calculation Based on Human Antomical Model
Authors: Liu Y , Zheng Y
Published: August 2010

Purpose: We performed a study to investigate the tissue composition effect on proton dose distribution. Dose calculation was performed based on a human anatomical model, and compared with that based on stopping power. Method and Materials: Currently, most proton treatment planning systems (TPS) employ a stopping‐power‐based dose algorithm for proton dose calculation, which do not model the tissue composition effect well due to the complicity of human anatomy. To overcome the limitation of general TPSs, Monte Carlo methods provide a feasible and accurate dose calculation as they take into account detailed material properties, including tissue density and tissue composition. Monte Carlo simulation calculates the dose for each small volume (voxel) after a patient is converted to a model consisting of a huge amount of tissue voxels. To obtain an accurate human anatomical model, the data set from the Nation Library of Medicine's Visible Human Project has been adapted in this study. A patient (actually a cadaver) was segmented with anatomical detailed materials assigned for each slice. Dose distribution and dose volume histogram were calculated using both MC simulations based on the anatomy models and TPS calculation, and compared with each other. Results: Dose volume history for planning tumor volume (PTV), Brain, Pituitary and Chiasm were used for evaluating the effect of tissue composition. The mean dose difference for PTV was 2.3% for the cadaver‐based MC simulation and TPS calculation. The mean dose differences for Brain, Pituitary and Chiasm were between 1.0% and 1.5%. Conclusion: Proton radiation dose was calculated and closely compared using MC simulation and TPS calculation. It is found that human tissue composition contributes on proton radiation dose calculation to some level. Further study is needed to determine whether the effect of tissue composition on proton dose calculation is clinically significant.
SU‐GG‐T‐425: Modeling a Multi Leaf Collimator for IMRT Monte Carlo Dose Calculations
Authors: Craig J , Mulligan M , Chen J , Wong E
Published: August 2010

Purpose: To investigate the effects of modeling a multi leaf collimator (MLC) with a simplified discrete block geometry for Monte Carlo (MC) simulations. Method and Materials: In our MC simulations (NxEGS NumeriX, LLC) we modeled each leaf in the MLC using 3 layers of staggered blocks to simulate the rounded tip, tongue and groove, and leaf divergence. Dose calculations were compared against measurements and the collapsed cone convolution algorithm in Pinnacle. Profiles from a water phantom were measured with ion chamber or diode both orthogonally and parallel to leaf travel directions for field sizes of 15×15cm, 10×10cm, 5×5cm, 3×3cm, and 2×2cm (with jaws always set to 20×20cm). Two abutting 10×5cm fields were measured with film on a solid water phantom, to determine how well the simulations handle the tongue and groove effect. A 3‐field IMRT lung patient was also planned and simulated on both the patient CT and a solid water phantom. Results: Gamma analysis (3mm/3%) comparing MC dose calculations and measurements for the range of the 2×2cm to 15×15cm fields collimated by the MLC showed good agreement. Results for the two abutting 10×5cm fields indicates NxEGS is modeling the tongue and groove effect, where as Pinnacle has under estimated it. When the IMRT lung patient plan was evaluated by MC calculations and Pinnacle on the solid water phantom, < 2% of points failed the gamma analysis (3%/3mm) whereas ∼5% increase in dose in the lung was observed in the MC dose calculation when compared to Pinnacle. Conclusion: A 3‐layer block geometry for modeling the MLC rounded leaf, divergence and tongue and groove is easily implemented, forgoing the minute details of a MLC, while still giving an accurate distribution as compared to both measurements. This can be used to verify dose distributions in 3D for IMRT treatment plans.
SU‐GG‐T‐433: Study of the Dose Distributions in Serial and Helical Tomotherapy for CO‐60, 6MV and 10MV Beams Using PENELOPE Monte Carlo
Authors: Gonçalves LR , Nicolucci P
Published: August 2010

Purpose: Study the dose distributions for 60Co, 6MV and 10MV beams in tomotherapy through PENELOPE Monte Carlo code. Methods and materials: PENELOPE was modified to simulate beam movement like used in serial and helical tomotherapy technique. The dose distributions in tomotherapy were simulated with a cylindrical phantom of 5 cm radius and 10 cm length. To simulate serial tomotherapy, the slice was obtained in 1 degree intervals until complete 360 degrees. A superposition software was developed in MatLab to obtain multi slices. To simulate the helical movement of the beam, relative to phantom length, for each rotation of 1 degree, the beam was displaced 0.00125 cm longitudinally. The SADs were 80 cm, 100 cm and 100 cm respectively to each beam, with a no modulate field of 1 × 1 cm2. To evaluate the simulated dose distributions the conformity index and Dose‐Volume Histograms (DVH) were used. A cylindrical Planned Target Volume of 0.2 cm radius and 2.2 cm length and an adjacent cylindrical ring organ‐at‐risk of 0.2 cm internal radius, 0.5 cm external radius and 4.4 cm length were defined inside the phantom. Results: The obtained conformity indexes were 0.78, 0.85 and 1 to serial tomotherapy and 0.67, 0.98 and 0.98 to helical tomotherapy to 60Co, 6MV and 10MV, respectively. Conclusions: In the serial tomotherapy 60Co and 6MV have shown similar behavior and have spared health tissues better than 10MV. To helical tomotherapy 6MV and 10MV have shown similar behavior but 60Co has shown a better sparing of health tissues while losing dose conformity. Helical tomotherapy conformed the dose in target volume better than serial tomotherapy, without hotspots.
SU‐GG‐T‐434: A Joint Research Investigation Comparing MCNPX and Geant4 Monte Carlo Codes to Reduce the Range Uncertainties in Proton Therapy
Authors: Bednarz B , Mirkovic D , Titt U , Paganetti H
Published: August 2010

Purpose: Advanced technology may help control the depth of the dose delivered to anatomical regions in the patient with a accuracy close to 1 mm. Monte Carlo methods are able to precisely model the transport of protons within the patient offering the potential to assist in achieving this level of accuracy. Both MCNPX and Geant4 Monte Carlo codes have been used for proton beam therapy simulations. However, to our knowledge very little has been done to compare the inherent differences in the handling of proton transport between the two codes. Methods: A detailed comparison of proton dose distributions within a variety of phantoms was performed between MCNPX and Geant4. Simulations were done using a generic water phantom, a complex phantom with bone and lung components, and a patient phantom produced from CT data. A spread‐out Bragg peak proton beam with a range of 17.3 cm and a modulation width of 5 cm was considered. A qualitative comparison investigating the differences between dose distributions together with quantitative comparisons using gamma analysis was completed. Results: The MCNPX and Geant4 dose distributions agreed very well for most cases. For all curves considered the gamma analysis yielded at least 90% of the points within the 2% and 2 mm criteria. There appears to be a slight disagreement in the uniformity of SOBPs in the water and complex phantom. Conclusion: This study improves our understanding of the differences in the proton dose deposition predicted from MCNPX and Geant4 Monte Carlo codes.
SU‐GG‐T‐436: Monte Carlo Optimisation of a BNCT Facility Including Multiplier, Reflector, Filter and Modrator for D‐T Source
Authors: Eskandari M , Mostafaei F , Salimi E , Kashian S
Published: August 2010

Purpose : Boron neutron capture therapy (BNCT) is currently an outstanding treatment for patients afflicted by deadly brain cancer (GlioBlastoma Multiforme) or Melanoma. Epithermal neutrons with energy from 1 eV to10 keV represent the most effective range for brain tumor therapy. Method and Materials :In this study we have focused on D‐T generator as a neutron source. The Monte Carlo code (MCNP4C) has been used in simulation of producing system of epithermal neutrons. For this purpose, we have studied four different neutron multipliers (Pb,U,Bi and Be) and their combinations, six different neutron moderators (H2O, D2O,AlF3, Polystyrene, Plexiglas, and paraffin) five filters (Al, Fe,S,Ni, and liquid Argon) and Beo as a reflector. Results :Results show that, by selecting Bi and 238U as neutron multipliers, AlF3 as a moderator and Ni and BeO as a filter and reflector respectively. Conclusions : By this results, the optimum epithermal neutron in such system is obtained.
SU‐GG‐T‐442: Dose Verification of SRS Monte Carlo Plan with a Moving Anthropomorphic Phantom
Authors: Lo A , Ho A , Dieterich S
Published: August 2010

Purpose: Dose verification of Stereotactic Radiosurgery plan using Monte Carlo for tissue heterogeneity correction with a moving anthropomorphic phantom Method and Materials: An anthropomorphic lung phantom has gold fiducials, TLD capsules and GAFChromic films imbedded in a target in the left lung, TLD capsules are also inserted in heart and cord structures. The phantom was scanned, CT images were sent to Cyberknife Multiplan for planning. Target and critical structures were contoured. A SRS treatment plan with no tissue heterogeneity correction was generated to give 6Gy to 95% of the target, 5.4Gy to 99% of the target, no point > 2cm from target > 3.5Gy, conformai index < 1.2, cord < 1.8Gy, heart < 3Gy, 10% of whole lung < 2Gy. The plan was recalculated with Monte Carlo with 2% uncertainty for tissue heterogeneity correction for dose delivery. During delivery the phantom moved in superior/inferior and anterior/posterior direction, Cyberknife Synchrony tracking system took orthogonal x‐ray images of the phantom while infra‐red camera tracked LED diodes placed on the phantom to track phantom motion in real time. After the fiducials were identified by the tracking program and correlated with the motion of LED diodes, a motion model of the target was built; radiation started with the Cyberknife robot following the predicted target motion and adjusted its position during irradiation. Throughout delivery, the motion model was updated and adjusted with new x‐ray images of the fiducials. Results: Target TLD was 98.3% of Monte Carlo dose; heart and cord TLD were within 7% acceptability. Profiles from 3 orthogonal films were displaced L/R 0mm/3mm, P/A 1mm/5mm and I/S 1mm/2mm from treatment plan profiles, within 5mm acceptability. Conclusion: Cyberknife Multiplan with Monte Carlo accurately predicts dose in heterogeneous tissue; Cyberknife Synchrony tracking system delivers dose accurately to a target in a moving phantom.
SU‐GG‐T‐445: Sequential Treatment of Brain Metastases Using a Markov Decision Process
Authors: Phillips M , Zhang P , Kim M , Ghate A
Published: August 2010

Purpose: To use a Markov Decision Process (MDP) to model the sequential treatment of recurrent brain metastases. The purpose of the model is to calculate the optimal set of treatment decisions given the state of the patient. Improved systemic cancer control has resulted in growing numbers of patients who undergo multiple treatments for brain metastases. Given this situation, it is important to determine the optimal treatment decision at any point in time given the condition of the patient and the possibility of future treatments. Methods: Sequential stochastic decisions can be optimized with respect to a given reward using dynamic programming methods. A model of patients with brain metastases was constructed using a definition of state, a set of actions (whole brain RT, surgery, stereotactic radiosurgery, waiting), transition probabilities between states dependent on a given action, and a reward based on quality of life. Transition probabilities were obtained from the literature and clinical data. The problem was solved for both an infinite horizon, resulting in a stationary policy, and a fixed horizon, resulting in optimal decisions for each decision epoch. Results: The model was developed and validated by comparison with clinical judgment. Selection of adequate state variables and suitable rewards was made by comparing optimal policies with standard clinical situations. After the development phase, the model was used to study the role that possible subsequent treatments have on optimal decisions. The effects of knowledge regarding expected lifespan on optimal policies was investigated. In addition, comparisons of stationary policies with finite horizon policies were made. Conclusion: A first attempt at applying MDPs to radiation therapy decision making focussed on improving treatment strategies for metastatic brain cancer. An important application of this model will be to determine the extent to which improvements in our knowledge of a patient's prognosis will alter recommended therapies.
SU‐GG‐T‐447: Interplay between Prostate Intra‐Fraction Motion and Proton Uniform Scanning Treatment: A Dosimetry Study
Authors: Su Z , Slopsema R , Flampouri S , Li Z
Published: August 2010

Purpose: To investigate dosimetric impact of prostate intra‐fraction motion to proton uniform scanning (US) treatment using Calypso prostate tracking data and a validated in‐house dosimetry analysis software. Method and Materials: Uniform scanning (energy stacking) delivers energy layers from distal to proximal temporally, which interplays with prostate intra‐fraction motion. In‐house software was developed to simulate the interplay and evaluate its dosimetry impact. It imports patient contour structures and dose matrix from treatment planning system (TPS) and de‐convolved it into temporal‐spatial dose matrix that indexed by energy layers. CTV was rigidly moved through the temporal‐spatial dose matrix according to prostate motion traces. Validation of the software was performed against Eclipse Proton TPS. 17 patient prostate intra‐fraction motion traces were used to evaluate prostate CTV dosimetry. For comparison, double scattering (DS) treatment was also simulated using the same prostate motion traces. Furthermore, higher dose rate was simulated for both US and DS treatments to evaluate its effect. Results: Software validation indicated that its difference to TPS calculation is minimum. For patient treatment simulation, the results indicated that CTV dose degradation depends on magnitude and direction of prostate intra‐fraction motion and is patient specific. In fractions with significant motion, 100% dose coverage can reduce to 66% and 78% of CTV for US and DS treatments, respectively. DVH and isodose graphs revealed significant CTV cold/hot spots in US and only CTV underdose in DS treatment. Higher dose rate caused more dose degradation. Conclusion: Intra‐fraction prostate motion causes dose uncertainty in proton treatment. The interplays between temporal delivery of energy layers and prostate motion in US treatment further degrade planned dosimetry and cause hot and cold spots inside CTV compared to DS treatment. This study indicated that such significant CTV dose inhomogeneity may exist for some patients with severe prostate intra‐fraction motion during US treatments.
SU‐GG‐T‐450: An Analytical LET Model for Fragmenting Ion Beams
Authors: Frese M , Oelfke U
Published: August 2010

Purpose: To provide a fast analytical model to calculate the dose and the dose‐averaged linear energy transfer (LET) of fragmenting ion beams.Method and Materials: An analytical model to calculate the stopping power of primary ions and their fragments was derived. It is based on a power law for the range of protons as a function of their energy and was derived both with and without consideration of nuclear interactions in terms of depth straggling. Two major assumptions were made: (1) fragments are always remnants of primary ions and not of target atoms and (2) the energy per nucleon is preserved during fragmentation. Cross sections for the fragmentation are not provided but were derived from Monte Carlo simulations. Dose and LET are calculated for primary ions and each isotope created in the fragmentation process individually. Results: The depth dose curves of the analytical model could reproduce those of a Monte Carlo simulation for a primary carbon ion beam and all its fragment elements but hydrogen. A previously published analytical LET model confirmed the LET calculations of fragments in depths less than the depth Rf of the peak dose. Including straggling introduces distinct changes in the LET of fragments at depths greater than of Rf. The changes in the LET at smaller depths than Rf and in the dose at any depth are marginal. Conclusion: The novel analytical model provides a fast way to calculate the dose and the LET for fragmenting ion beams. Several profound assumptions had to be made to obtain an analytical solution. The agreement of our dose calculations with Monte Carlo simulations showed that these can be justified. The LET calculations are sufficiently accurate for their use in modeling of biological effects.
SU‐GG‐T‐452: In‐Vivo Dosimetry Using a MOSFET Detector in an Anthropomorphic Phantom for Therapeutic Proton Beam
Authors: Kohno R , Hotta K , Matsubara K , Matsuura T , Kameoka S , Nisiho T , Kawashima M , Ogino T
Published: August 2010

Propose: In‐vivo proton dosimetry can be used to identify major deviations in a delivery of treatment. We challenged in‐vivo measurements with a MOSFET detector for an anthropomorphic phantom with tissue inhomogeneities. Here, The MOSFET response depends strongly on the linear energy transfer (LET) for proton beam. Therefore, we developed a method to correct the MOSFET response for the LET dependence by using a simplified Monte Carlo dose calculation method (SMC). Method and Materials: A depth‐output curve in polyethylene for mono‐energetic proton beam was measured with the MOSFET detector. To calculate MOSFET output distributions, the SMC (SMCMOSFET) used the depth‐output curve. Then, the MOSFET output value at an arbitrary point obtained by the SMCMOSFET were compared with a dose value obtained by a conventional SMC, which calculates proton dose distributions by using the depth‐dose curve measured with an ionization chamber. From the ratio of both values, we can calculate the correction factor of the MOSFET response at the arbitrary point. Finally, the dose obtained by the MOSFET detector is given by the product of the correction factor and the MOSFET raw dose without the above correction. We performed in‐vivo proton dosimetry with the MOSFET detector in head and neck regions of an anthropomorphic phantom. Results: The results measured by the MOSFET without the correction at each measurement condition indicate a remarkable deviation from those of the SMC. On the other hand, the corrected MOSFET doses agreed with the results of the SMC within the measurement error. Conclusion: For dose measurements in the anthropomorphic phantom with tissue inhomogeneities, the corrected MOSFET dose agreed well with the SMC results within the measurement error. Using the correction method for the MOSFET response, we could succeed in‐vivo proton dosimetry with the MOSFET detectors for the first time.
SU‐GG‐T‐522: Investigation of Intracranial Localization for SRS and SRT Using MV‐CBCT
Authors: Johnson M , Gayou O
Published: August 2010

Purpose: To investigate the accuracy and precision of Mega‐Voltage Cone Beam Computed Tomography (MV‐CBCT) localization for intracranial stereotactic treatment deliveries. Method and Materials: A Rando head phantom containing a metal ball bearing (BB) was mounted with a head frame. A treatment plan targeting the BB was generated and three localization methods were compared. The first, was the standard technique using laser micro‐alignment to the isocenter projected onto target positioning sheets. Second, a standard MV‐CBCT was acquired, using skull based registration with the treatment planning CT and millimeter precision correction using the motorized treatment couch. For the third, a micro‐adjustment of the head frame position using a Vernier scale was used to apply the MV‐CBCT correction with a 0.1 mm accuracy. After localization with each method was achieved, a series of 1.0 × 1.0 cm fields from gantry angles 0, 90, 180 and 270 degrees was used to asses target alignment by measuring the BB position relative to the beam central axis. Results: The standard localization technique resulted in an average displacement of the BB with respect to the beam central axis of 1.2 ± 0.1 mm. Skull‐based localization with MV‐CBCT using millimeter precision couch offsets resulted in a displacement of the BB with respect to the beam central axis of 2.3 mm. Localization with MV‐CBCT and micro‐adjustment resulted in a displacement of the BB with respect to the beam central axis of 1.2 ± 0.2 mm. Conclusion: After modifications were applied to the MV‐CBCT localization technique, accuracy was as good as the standard approach for head frame cases. When MV‐CBCT localization is applied to a frameless case, the anatomy‐based alignment eliminates the variability of interfraction patient positioning within the immobilizing mask.

Conflict of Interest: Research partially funded by Siemens Medical Solutions.
SU‐GG‐T‐523: A Creative Measure to Ensure the Accuracy of Removable SRS Mask
Authors: Shang C , Vargas C , Schramm A , Sckolnik J
Published: August 2010

Purposes: To analyze geometrical uncertainties of Brainlab SRS head mask system during clinical practice, and evaluate the effectiveness in limiting the uncertainty by introducing a special longitudinal restraint. Material and Method: From June, 2009 to February, 2010, total 24 intracranial lesions were treated with Brainlab SRS mask system on Varian NTX at our center. All patients were immobilized with Brainlab head mask system, which was made about 15 minutes prior to simulation. The removable frame consists of a back and front thermoplastic mashes; reinforcing pieces cross the forehead and upper lip attached by a nose bridge and bite pieces. In the test group, a longitudinal restraint was extended cross the top of head. The mask is attached to a U shaped base ring for rigid geometric registration of simulation CT. During the treatment the setup of Brainlab's localizer was compared with CBCT. Results: The mean 3D displacement of 16 cases with Brainlab SRS mask was 4.1 ±1.5mm. Their vertical, longitudinal, and lateral shifts were 1.6 ±1.0mm, 3.2 ±1.9mm (p < 0.01), and 1.1 ±0.9mm respectively. Averaging all 8 cases in the test group using the longitudinal constraint, the shift was reduced to 0.3 ±0.5 mm (p<0.01). The only 2 cases were shifted, only by 1mm, and identified after CBCT to be caused by operator's oversight. Conclusion: During treatment setups for less cooperative patients, the accuracy of commercial Brainlab SRS head mask system can be easily compromised due to altered the pitch angle or longitudinal position of the head inside the mask. Due to this reason, we found greater variations in our practice for SRS setups using Brainlab's removable frame. The introduction of longitudinal restraint has demonstrated its effectiveness in ensuring the accuracy of this system.
SU‐GG‐T‐524: Evaluation of RapidArc vs. Static Intensity‐Modulated Radiosurgery in the Single‐Isocenter Approach for Multiple Brain Metastases
Authors: Wang J , Pawlicki T , Rice R , Mundt A , Murphy K
Published: August 2010

Purpose: RapidArc has the advantage of reducing the MUs in dose delivery. This study reports the comparison of the beam arrangement and MU reductions of RapidArc (RA) and IMRT based radiosurgery (IMRS) for the treatment of multiple intracranial metastases. Method and Materials: Twelve patients with multiple brain metastases treated with IMRS were re‐planned with RapidArc. All the IMRS were delivered in a single fraction, single‐isocenter approach using 8–11 static beams. The prescribed dose was 18–20 Gy and the normalization as 100% of prescription dose covering 98% of PTV. Across patients, all the RA‐plans used 2‐coplanar arcs and followed systematic strategies in optimization objectives and MU limits. For each patient, two or more RapidArc plans were generated, and the plan with lower MU and higher conformity was chosen for comparison. Results: It is found that the MU reduction by RapidArc is more predominant for larger number of brain lesions, as the MU‐ratio of RA and IMRS was reduced from 92% to 39% as lesion number increased from 2 to 12. Also, the strategy of using only two coplanar arcs was based on the realization that it has a better dose conformity with comparable amount of total MUs as compared with a single‐arc approach. The 2‐coplanar‐arcs is also favorable as compared to more arcs as adding vertical or oblique arcs actually increases the dose to the normal brain and brainstem with little benefit to the PTV dose conformity. Conclusion: The MU reduction of RapidArc is more significant in intracranial radiosurgery. RapidArc uses much fewer MUs in radiosurgery as compared to those in the static 9‐beam IMRS treatment. The total treatment time is reduced even more, as two co‐planar arcs with zero couch position further reduced the beam setup time as compared to 6–9 couch positions normally used in the IMRS treatment..
SU‐GG‐T‐525: Quantification of the Peripheral Dose Components in Perfexion
Authors: Nayebi N , Ruschin M , Nordström H , Johansson J , Eriksson M , Kjäll P , Jaffray D
Published: August 2010

Purpose: To explore the possibility of separately quantifying the leakage and scatter components of the peripheral radiation dose resulting from Leksell GammaKnifeR Perfexion™ radiotherapy. Methods and Materials: In this study, peripheral dose was defined as the dose arising at points outside the paths of the primary beams. Consider a spherical skull phantom centered at Leksell coordinates (100,100,100). Peripheral dose may arise from: (1) Inphantom scattered radiation originating from primary beams; (2) Radiation first scattered within the collimator structure (3) Photons undergoing multiple scattering and exiting through adjacent collimator openings and (4) Leakage radiation that passes directly through the collimator body. Contributions (1) and (2) were separately quantified via Monte‐Carlo simulations. Types (3) and (4) were measured using EBTII Gafchromic film inserts and placing the sources in“beam‐off” position (i.e. between collimator openings). Additionally, the total peripheral dose arising from a 16‐mm shot was measured using film. The combination of simulated type_1 and type_2 doses and measured type_3 and type_4 were compared to the measured total dose at 40 mm superior and inferior to the isocentre. Results: At the isocentre of the 16‐mm shot, the dose‐rate determined by Monte Carlo simulations agreed with measured dose‐rates to 0.8%, thereby establishing consistency between measurement and simulation. The simulated sum of Type_1 and Type_2 contributions at 40 mm inferior and superior to the isocentre was 0.40% and 0.35% of the isocentre dose‐rate, respectively. Of those totals, 87% was Type_1 a 13% came from Type 2. The measured total peripheral dose‐rate was 0.40% and 0.38% at 40 mm inferiorly and superiorly, respectively. The measured Type_3 and Type_4 dose‐rates were less than 0.01% of the isocentre dose‐rate in either direction. Conclusion: The results of this study indicate that peripheral dose arising from a single 16‐mm shot arises primarily from Type_1, with <0.01% contribution from leakage radiation.
SU‐GG‐T‐527: Patient Specific Delivery Quality Assurance for Robotic Stereotactic Radiosurgery of Functional Targets
Authors: Hsu A , Wang L , Ho A , Dieterich S
Published: August 2010

Purpose: Develop and implement a patient‐specific delivery QA (DQA) procedure for small functional targets treated with radiosurgery using a Cyberknife. The procedure verifies both the dose and targeting accuracy. Method and Materials: Cyberknife treatment plans (Multiplan v3.5) for functional targets were created. Phantom overlay plans were created using a head and neck phantom with the BallCubeII insert to a maximum dose of 6Gy. Specially cut EBT2 GaFchromic film was oriented orthogonally within the BallCubeII. The target dose distribution was placed such that high dose was on both pieces of film. The phantoms overlay plan was delivered and the film analyzed using FilmQA (3cognition) with an automatic detection component specific for the BallCubeII. A dose calibration curve was created using film from the same lot. The differences between the planned and delivered doses for each user defined ROI were determined, along with the distance to agreement (DTA) and gamma index (γ) values. Results: A number of different criteria were considered including γ (3%, 1mm), DTA (1mm) and dose difference (±5%, ±10%, ±15%). In general, all points (∼100%) within the ROI passed the DTA (1mm) and scored highly for γ index (3%, 1mm). Dose differences (Δdose ±5) for plans using 5mm and 7.5mm cones scored worse (20–50% passing) than those using 7.5mm cones and larger. For Δdose ±10%, the 5mm cone plans scored ∼80% pass rate. All plans passed Δdose ±15%. Conclusion: We have developed a patient‐specific delivery QA procedure using a phantom overlay plan delivered to EBT2 film in the BallCubeII insert and analyzed with FilmQA. Dose distributions and targeting accuracy were excellent. For small targets near an organ at risk, the dose discrepancy should be considered as well as the gamma index during patient specific delivery QA for small targets.