bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐375: A Custom‐Developed Method for Accurate Dose Recalculation of Patient Plans Entered into Clinical Trials
Authors: Davidson S , Kry S , Cui J , Deasy J , Ibbott G , Vicic M , White R , Followill D
Published: August 2010

Purpose: To compare a custom‐developed method for accurate dose recalculation of patient plans entered into clinical trials with results from a common treatment planning system. Method and Materials: A measurement‐driven multiple‐source model with the Dose Planning Method (DPM) Monte Carlo (MC) dose calculation algorithm was previously developed, validated, and benchmarked for the Varian 6 MV and 10 MV photon beams. Several patient cases have been recalculated and compared to the calculations from a Pinnacle planning system. Intensity modulated radiation therapy (IMRT) prostate, IMRT abdomen, stereotactic body radiotherapy lung, and IMRT lung patient cases were selected. Results: Field sizes from 4 cm × 4 cm to 40 cm × 40 cm were validated to within 2% of the maximum dose and 2 mm distance to agreement. At least 95% of the data tested met the validation criteria. Benchmark treatments planned using anthropomorphic phantoms were tested to within 3% of the target dose and 2 mm distance to agreement. At least 85% of the data tested met the benchmark criteria. Disagreement in the patient plan evaluation tended to occur at heterogeneity interfaces where electronic disequilibrium occurred, and in the beam penumbra, where scattered radiation was more prominent. The ratios of planning system calculation to MC calculation for the mean dose of the gross and planning target volumes for the patient plans ranged from 0.984 to 1.016. Conclusion: These results show that this MC software code generates answers similar to the Pinnacle system for IMRT and SBRT treatment plans. Differences are consistent with the superior physics modeling inherent in the Monte Carlo code. We believe the method will be useful for recalculating dose distributions for patients entered into clinical trials. Work supported by PHS CA010953, CA081647, and R01 CA85181 awarded by NCI, DHHS
SU‐GG‐T‐376: Medical Physics Calculations in the Cloud: A New Paradigm for Clinical Computing
Authors: Keyes R , Romano C , Arnold D , Luan S
Published: August 2010

Purpose: The accuracy of medical physics calculations is largely limited by the availability of fast computer hardware, which is in turn strongly limited by budget considerations. This research explores the use of the Cloud Computing paradigm to replace or supplement existing computing infrastructure for medical physics calculations. Cloud computing services allow for on‐demand virtual computing clusters with a pay‐as‐you‐go pricing model. This model has the potential to make large scale Monte Carlo simulations routine in clinical and research activities. Methods and materials: To test the feasibility of medical physics calculations in a cloud computing environment, a distributed Monte Carlo dose calculation framework was implemented with Amazon's EC2 cloud computing service, the Fluka 2008.3b Monte Carlo package, a distributed processing framework written in Python, and the Hadoop MapReduce framework. A variety of relevant calculations were performed: depth dose profiles of proton, electron, and photon beams, along with a simple proton treatment plan using a voxel patient geometry (Zubal phantom). The performance of EC2 was tested by running calculations on 1 to 200 virtual nodes with the different distributed processing frameworks. EC2 prices were compared with costs of comparable local hardware. Results: Relevant medical physics calculations were successfully carried out using the EC2 service. Heavy charged particle, electron, and photon depth dose profiles and a simple treatment plan were successfully calculated remotely. Performance data demonstrated the expected 1/n speed‐up as a function of node number. Two different distributed processing schemes were implemented in the cloud. Conclusion: Our implementations demonstrate the power of the existing cloud computing model. The relatively cheap pay‐as‐you‐go pricing for infrastructure on demand offers an extremely promising new paradigm for clinical and research computing, available to anyone with a network connection.
SU‐GG‐T‐378: A Monte Carlo Simulation Method for Treatment Planning Optimization of Eye Plaques Using MCNP4C Code
Authors: Shokrani P , Raisali G , Esfahani A Janati , Ghonchenazi M Ghasemi
Published: August 2010

Purpose: Ophthalmic plaque radiotherapy using I‐125 radioactive seeds in removable episcleral plaques is often used in management of ophthalmic tumors. The goal of this study was to develop a Monte Carlo simulation method for treatment planning optimization of eye plaques. Method and Materials: MCNP4C Monte Carlo Code was used to calculate the percent depth dose curves, dose profiles and isodose curves created by three different plaques. The plaques used were Collaborative Ocular Melanoma Study‐12mm (C0MS‐12mm) with eight model 6702 seeds, COMS‐20mm with three model 6711 seeds, and University of Southern California (USC) #9 with nine model 6711 seeds. Dosimetric characteristics of I‐125 model 6702 and 671 seeds, were calculated according to recommendations of AAPM Task Group 43 protocol. Then, the geometry of each plaque was simulated and dose calculations were performed using F6 tally card in a 12mm radius spherical water phantom. Results: The comparison of calculated central axis depth doses to reported measured values, showed the deviation up to %10 for C0MS‐12mm, %3 for COMS‐20mm and %1 for USC#9. For off‐axis dose profiles the deviation was up to %9 for C0MS‐12mm, at 7mm depth, %6 for COMS‐20mm at 10mm depth and %1 for USC#9 at 17 mm depth. The results of this study show that C0MS‐12mm and COMS‐20mm plaques are suitable for treatment of symmetrical tumors with thickness‐diameter (base) of 8mm‐14mm and 4mm‐12mm, respectively. However, a USC#9 plaque is suitable for treatment of non‐symmetrical tumors with 8mm thickness and 16mm base diameter. Conclusion: The user code developed in this study can be used as an optimization tool within a few millimeters of the plaque surface. It can also be used to design custom made plaques for treatment of ocular tumors with various sizes, shapes and locations.
SU‐GG‐T‐381: Monte Carlo Study of Neutron Dose Equivalent for a Compact Proton Therapy Unit
Authors: Zheng Y , Klein E , Chen K , Liu Y
Published: August 2010

Purpose: A compact proton therapy unit (Still River Systems, Littleton, MA) is under development. This will be the first such unit in the world and neutron exposure for this machine is unknown. Our purpose is, using Monte Carlo methods, to model the detailed beam line, simulate neutron fluence, and estimate neutron dose equivalent for this proton therapy unit. Method and Materials: The compact proton therapy unit utilizes a synchrocyclotron, which will be aligned together with the beam shaping system (BSS) in a single room. We modeled the proton source coming out of the cyclotron as a Gaussian distribution with a mean energy of 250 MeV. The BSS uses passive scattering techniques to spread out the beam laterally and in depth. We modeled each BSS component in detail according to the design data provided by the manufacturer. The MCNPX code (Version 2.5.0) system was used. The neutron spectral fluence in air was simulated with a closed aperture and without range modulation. Neutron dose equivalents were then calculated using the neutron fluence to dose equivalent conversion factors based on ICRP publication 74. Up to 108 proton histories were tracked per simulation. Results: Fourteen options (combinations of modulator wheel and scatterer) were modeled. Neutron spectral fluence was simulated and analyzed. The neutron dose equivalent per therapeutic proton dose (H/D) at isocenter ranged from 0.82 mSv/Gy for a shallow range and small field size option, and up to 17.4 mSv Gy−1 for a deep penetrating, and large field size option. Conclusion: The H/D values from this compact unit are comparable to those from conventional multi‐room proton therapy units employing passive scattering techniques. The H/D values decrease with decreasing maximum treatment depth (range), but are relatively higher for very shallow range options, compared with existing passive scattering units.
SU‐GG‐T‐382: Evaluation of Genipin Gel Dosimeter for Depth Dose Measurement of X‐Ray Beams
Authors: Gorjiara T , Hill R , Kuncic Z , Baldock C
Published: August 2010

Purpose: To evaluate genipin gel dosimeter for depth dose measurement of x‐ray beams. Method and Materials: Differences in depth doses between the genipin gel dosimeter and water for clinical megavoltage and kilovoltage x‐ray beams was determined using Monte Carlo modeling. All the Monte Carlo calculations were performed using the EGSnrc/BEAMnrc package (V4 r2‐2‐5). The clinical x‐ray beams were generated from a Varian 21iXs linear accelerator generating 6MV x‐rays and a Pantak Therapax DXT300 kilovoltage x‐ray unit with a tube potentials from 50 to 280kVp. A higher energy kilovoltage x‐ray beam was also calculated by increasing the maximum energy of incident electron energy hitting the target to 350keV. The BEAMnrc user code was used to calculate the phase space files for each of the x‐ray beams. The generated phase space files by BEAMnrc were then used to calculate depth dose curves for the genipin gel dosimeter and water using the DOSXYZnrc user code. The dose in each phantom was defined as 60×60cm2 for 6MV and 20×20cm2 for kilovoltage energies in the lateral planes while along the depth direction, smaller voxel sizes (Minimum voxel thickness of 0.25cm for 6MV and 0.5cm for kilovoltage energies) were used in the dose buildup region. Results: For the calculated depth dose using the 6MV x‐ray beam, there were differences of less than 1% between the genipin gel dosimeter and water. For the kilovoltage energies, the relative difference in the depth doses of the genipin gel dosimeter and water is approximately 2% for the 50 and 75kVp photon beams, 1% for the 100 and 125kVp photon beams, 0.5% for 180 and 200kVp photon beams and less than 0.1% for 250–350kVp photon beams. Conclusion: According to this result, genipin gel dosimeter is a water equivalent dosimeter for depth dose measurement of the clinical 6MV and kilovoltage photon beams.
SU‐GG‐T‐384: Validation of an Electron Monte Carlo Dose Calculation Algorithm in the Presence of Heterogeneities Using Radiochromic Film
Authors: Aubry J , Bouchard H , Doucet R , Lacroix F
Published: August 2010

Purpose: To validate electron beam dose distributions calculated with the electron Monte Carlo (eMC) algorithm in situations of bone and lung heterogeneities using radiochromic films. Method and Materials: Four heterogeneous phantoms are used in this study. Radiochromic films are inserted in these phantoms, including in heterogeneous media, and the measured relative dose distributions are compared to eMC calculations. Phantoms A, B and C contain 1D heterogeneities, built with layers of lung and bone equivalent materials sandwiched in Plastic Water. Phantom A has 1.5 cm of Plastic Water, 9 cm of lung material, and 5 cm of Plastic Water. Phantom B has 1 cm of Plastic Water, 1 cm of bone material, and 5 cm of Plastic Water. Phantom C is similar to phantom B but has 2 cm of bone material. Phantom D is a thorax anthropomorphic phantom with 2D lung heterogeneities. Electron beams of 6, 9, 12 and 18 MeV are delivered to these phantoms with a 10×10 cm2 applicator. Results: Percent depth dose (PDD) film measurements and eMC calculations agree within 2% or 3 mm for phantom A, and within 3% or 3 mm for phantoms B and C for almost all beam energies. One exception is observed with phantom B and the 6 MeV, where measured and calculated PDDs differ by up to 4 mm. Gamma analysis of the measured and calculated 2D dose distributions in phantom D agree with criteria of [3%, 3 mm] for 9, 12 and 18 MeV beams, and [5%, 3 mm] for the 6 MeV beam. Conclusion: Dose calculations in heterogeneous media with eMC agree within 3% or 3 mm with radiochromic film measurements. 6 MeV beams are not modeled as accurately as other beam energies. The eMC algorithm is suitable for clinical dose calculations involving lung and bone heterogeneous media.
SU‐GG‐T‐385: Dose Perturbation by a Steel Magnetic Injection Port in a Breast Tissue Expander in Proton Radiotherapy: A Monte Carlo Study
Authors: Moskvin V , Das I , Cheng C , Zhao L , Wolanski M , Andrews J , Johnstone P
Published: August 2010

Introduction: The use of a tissue expander in breast reconstruction is a popular option for patients undergo mastectomy. We applied Monte Carlo simulation to analyze the dose deposition from proton beams in the presence of a tissue expander containing a steel magnetic injection port. Methods:. A steel injection port for breast tissue expander (Mentor®) was studied with a single anterior (AP) proton beam. A general‐purpose Monte Carlo particle transport code FLUKA was applied for simulation. A 10×10 cm beam was delivered to a water phantom of 50×50×50 cm with the port positioned at the surface. Data on the proton fluence and dose deposited in phantom were collected for a range of initial proton energies forming the spread out Bragg peak (SOBP) of 100 to 200 MeV. Results: Our simulation shows that low energy proton fluence is disturbed significantly by the presence of the steel injection port. Impact of the port components varies at the crossbeam plane. The needle shielding plate edge decreases fluence in the beam direction by almost at 30%. The proton range shifts about 50 % for lower energies (100 MeV) and 15% for higher energies (200 MeV). Dose changes at distances close to metal‐phantom interface are between 5 and 10%; however, there are dramatic changes (up to 100%) in dose deposition at deep areas where the SOBP suppose to form. Combining multiple beams with various energies and weights into SOBP will cause multiple spots of significant over‐ and under dose. Conclusions: The dose perturbation by a steel injection port for breast tissue expanders is significant if the implant is in a proton field. The accuracy in treatment planning with conventional algorithms may be questionable in the presence of the inhomogeneity. Avoidance of such metallic components should be considered if adjuvant proton radiotherapy is considered.
SU‐GG‐T‐388: Assessing Dose Inaccuracies in the Superposition/Convolution Algorithm with Monte Carlo for SBRT Lung Tumors
Authors: Seco J , Westover K , Willers H
Published: August 2010

Purpose: To assess dose inaccuracies in the superposition/convolution dose algorithm with Monte Carlo and how it affects SBRT lung treatments. Materials & Methods: The treatment strategy for the SBRT tumors at MGH is to use 3DCRT for tumors with motion amplitude of less 5mm. The SBRT treatment planning uses either 2 or 3 non‐coplanar arcs, with a total of 8–10 beams. Following the dose planning guidelines provide by RTOG 0813 and 0618, the PTV is conformed with an isodose between 60% and 80% value. This will guarantee that the penumbra tail does not extend to deeply into the lung, while manipulating the hotspots of 120–140%, such as to situate them within the PTV region. SBRT dose calculation is performed with the commercial CMS superposition/convolution algorithm (SCA) and verified with in‐house developed Monte Carlo (MC) dose engine. SCA was also compared with MC in heterogeneous GAMMEX phantom to assess in a wide range of heterogeneous materials the accuracy of SCA. Results: A cohort of 10 SBRT patients was studied with both SCA and MC dose algorithms comparing PTV coverage after dose normalization. The SCA was shown to incorrectly estimate the dose in the PTV by 1–3% relative to the MC prediction, before normalization. The SCA differences occurred when the tumor was situated very close to a bone structure, such as rib cage. Similar results were observed in the irradiation of the heterogeneous phantom. The SCA dose algorithm inaccurately predicts doses if the region is shadowed by a high density material such as bone. Conclusions: Lung Cancer is the number one cause of cancer mortality in both men and women. Inaccuracies in the SCA dose computation can affect the treatment outcome of SBRT. This study suggests that accurate dosimetry in SBRT treatment of lung patients requires the use of Monte Carlo techniques.
SU‐GG‐T‐391: Electron Beam Dose Modification Using Transverse MRI‐Linac B Fields; A Shielding‐Delivery Investigation
Authors: Koren S , Fourkal E , Tafo A Guemnie , Veltchev I , Ma C
Published: August 2010

Purpose: To examine magnetic field shielding possibilities in order to use the transverse magnetic field generated in MRI‐Linac system with electron beams. Method and Materials: Using a magnetic field with electron beams in order to increase the dose in the target organ while sparing the surrounding tissue, was suggested in the past. A transverse B field applied in depth is causing the electrons to spiral and deliver their energy in a smaller volume, generating a pseudo Bragg peak. The MRI‐Linac systems introduce up to 1.5 T transverse fields with respect to the beam direction. In order to facilitate this system for electron beam dose modification, an applicator that can shield the B field between the gantry and the patient is needed. This work estimates the shielding requirements for suggested applicator by using Comsol Multyphysic® to simulate the spatial magnetic fields. Those field map components are then exported to Fluka, a particle physics transport package, to transport the electron beam. Static and dynamic shielding concepts can be used. The static shielding is made in several lairs from varying materials (mu‐metal and Carbon steel), while the dynamic uses coils to compensate the field lines. Those high permeability materials have relative low saturation value, and hence their permeability reduces when introduced to high fields, according to their hysteresis curve. Results: Neglecting several practical issues, this initial research shows up to two fold depth dose increase with respect to the surface dose, for a 25.0 MeV beam. Nevertheless high magnetic field densities were observed from the static applicator simulation that requires further feasibility investigation. Conclusion: Clinical potential is shown using the transverse B filed with electron beam if proper shielding is achieved. Further investigation is needed to overcome shielding and practical drawbacks in order to facilitate this delivery.
SU‐GG‐T‐413: Comparison of Out‐Of‐Field Neutron Equivalent Doses in Scanning Carbon and Proton Therapies for Cranial Fields
Authors: Athar B , Henker K , Jäkel O , Bassler N , Paganetti H
Published: August 2010

Purpose: The purpose of this analysis is to compare the secondary neutron lateral doses from scanning carbon and proton beam therapies. Method and Materials: We simulated secondary neutron doses for out‐of‐field organs in an 11‐year old male patient. Scanned carbon and proton beams were simulated separately using Monte Carlo techniques. We have used circular aperture field of 6 cm in diameter as a representative field. The tumor was assumed to be in the cranium. The range and modulation width for both carbon and proton beams were set to 15 cm and 10 cm, respectively. Results: In carbon therapy, absorbed neutron doses to tonsils and pharynx close to the field‐edge were found to be 5×10−4 mSv/GyE and 4×10−4 mSv/GyE, respectively. Whereas, neutron equivalent doses to tonsils and pharynx were estimated to be 0.57 mSv/GyE and 0.55 mSv/GyE in scanned proton therapy, respectively. In heavy ion carbon beams neutrons produced inside the patient are emitted at small angles, predominantly in the forward direction, whereas in proton therapy, neutrons are emitted more isotropic. Therefore the absorbed neutron doses in carbon therapy lateral to the field edge are smaller compared to the corresponding proton fields. In forward direction though, the neutron doses from carbon ion therapy can be expected to be higher compared to proton therapy. Conclusions: Secondary neutron doses received by tonsils (out‐of‐field organ) in scanned carbon and proton therapies are found to be 5×10−4 mSv/GyE and 0.6 mSv/GyE, respectively. Organs located laterally away from the field‐edge receive much lower doses (thousand times smaller) in carbon therapy as compared to neutron doses in proton therapy. Whereas, on the distal side the neutron equivalent doses in scanned carbon therapy are a factor of 2 higher compared to similar scanned proton therapy fields.
SU‐GG‐T‐449: Dosimetric Impact of CT Metal Artifacts on Proton Pencil‐Beam Scanning Delivery
Authors: Verburg J , Joshi M , Bazalova M , Madden T , Kooy H , Seco J
Published: August 2010

Purpose: To quantify the dosimetric impact of CT metal artifacts on proton pencil‐beam scanning and passive scattering delivery. To develop a novel metal artifact reduction method to reduce artifacts in CT simulation images. Method and Materials: A tissue characterization phantom was scanned on a wide‐bore CT simulation scanner with and without metallic inserts. Original projection data was obtained for these scans. Images have been reconstructed with filtered back projection using both the original projection data and a version in which the projections through metal are restored with a 2‐dimensional interpolation method. A target volume (GTV) was defined in the center of the phantom. Dose errors were calculated by planning on the artifact‐affected images and calculating the dose on the ground truth images without artifacts. Results: Dose errors in the plan for passive scattering delivery mainly occurred around the edge of the GTV, caused by the range shift of the beams. The impact of metal artifacts on pencil‐beam scanning delivery is much greater; interplay between the pencil‐beams and local image artifacts results in dose errors of up to 18% inside the GTV. The dose errors in both plans could be reduced to 3% by applying the metal artifact reduction method to the CT data. Also, tissue structure that was originally hidden could largely be restored, which in patient plans can facilitate better delineation of the tumor and organs‐at‐risk. Conclusions: This work shows that metal artifacts in the CT simulation scan for proton pencil‐beam scanning delivery can result in significant under‐ and overdosage inside the GTV, which could lead to poor tumor control. A metal artifact reduction method has been developed and shown to reduce proton dose errors.
SU‐GG‐T‐515: The Influence of Longitudinal CT Resolution on Target Delineation and Treatment Planning for Stereotactic Radiosurgery
Authors: Bellon M , Siddiqui M , Movsas B , Chetty I
Published: August 2010

Purpose: To investigate the effect of longitudinal CT resolution on target delineation and treatment planning in stereotactic radiosurgery (SRS) to determine optimal acquisition parameters for SRS simulation. Method and Materials: CT images for 6 SRS brain patients were acquired and image sets were retrospectively reconstructed with 1, 2 and 3mm slice thicknesses. In total, 9 lesions were contoured 3 times each to quantify intra‐observer variability. The volumes contoured on the 2mm scan were the designated reference consistent with current clinical protocol. Variation in GTV with different CT slice thicknesses was evaluated. Additionally, treatment plans were created and optimized using the 2mm scans. Superimposing these plans on the 1mm and 3mm image sets provided a basis for dosimetric comparison—specifically in terms of target coverage. Results: All of the 3mm GTVs were larger than the 2mm GTVs. However, this consistent overestimation in the GTV was not observed at 1mm, suggesting that the 1mm and 2mm scans produced comparable GTVs. The average % difference in GTV volume when compared to the 2mm scans was 4.6% higher for the 3mm versus 1mm scans. Increasing CT slice thickness from 1 to 3mm caused an increase in the intra‐observer variation; volume standard deviations increased up to 51%. The intra‐observer variation also increased at larger tumor volumes. Average standard deviations (SD) in GTV extent were 0.14, 0.11 and 0.14cm in the sup‐inf, ant‐post, and lat dimensions, respectively, implying no directional dependence in target delineation. Dosimetrically, variations in GTV resulted up to a 19% loss in PTV dose coverage. Conclusion: This study indicates that longitudinal CT resolution causes considerable variation in GTV definition which can potentially compromise SRS treatment plan quality. Therefore, the SRS simulation process may benefit from improvement in scanning parameters in order to yield the most accurate information on the CT dataset.
SU‐GG‐T‐536: A New Treatment Plan Evaluation Index for Comparing Various SRS Treatment Technique
Authors: Chin J , Chin D , Medich D , Gao Z , French C , Tries M , Xu H , Acker B , Napier T , Yunes M , Kaufman S
Published: August 2010

Purpose: Proper evaluation of a stereotactic radiosurgery (SRS) plan is challenging due to lack of a comprehensive evaluation index and variation of dose prescription. In this study, a new treatment plan index is proposed to evaluate the quality of an SRS treatment plan by incorporating planning parameters that describe tumor coverage, dose to surrounding normal tissues, and tumor dose uniformity. Method and Materials: The proposed index contains four factors. The first factor is MDPD (ratio of the maximum dose to the prescription dose), which specifies the tumor uniformity. The second factor is V100, percent tumor volume covered by 100% prescription dose. The third factor is characteristic of dose spillage to normal tissue. The fourth factor is a piecewise function used to differentiate the deviation of the treatment plans from the requirement of RTOG protocol. Thirty‐four SRS cases fulfilling the requirement of RTOG protocol were analyzed by our proposed index and Paddick's index. Two dose prescription approaches were considered for this comparison: one is to maximize the tumor coverage and maintain plan uniformity; the other is to maximize the tumor coverage and spare the surrounding normal tissue. Results: Our result indicates that the proposed index becomes negative value when the tumor coverage or PITV significantly deviates from RTOG protocol. The treatment plan index for different lesion size, irregularity and location of critical structure relative to tumor target were calculated with various techniques at two different dose prescription approaches. Conclusion: Comparison of the plan index recommended by Paddick and that proposed in this study for clinical 34 SRS cases in Baystate Medical Center indicates that our plan index is reliable and sensitive to the lesion size, irregularity, and location of critical structures and is easier for the selection of the treatment techniques and dose prescription during the process of SRS.
SU‐GG‐T‐546: Dosimetric Impact of Beam Margin on 3D Conformal Treatment Plan in the Lung Cancer Stereotactic Body Radiotherapy
Authors: Jin L , Price R , Wang L , Fan J , Turaka A , Buyyounouski M , Ma C
Published: August 2010

Purpose: This work investigates dosimetrically how beam margin (BM) affects characteristics of 3D conformal lung cancer stereotactic body radiotherapy (SBRT) treatment planning in terms of the conformality index (CI), high‐dose spillage and intermediate‐dose spillage. Method and Materials: Ten patient plans were generated in the Eclipse treatment planning system using the Anisotropic Analytical Algorithm (AAA) for BM of 0, 2 and 4 mm, respectively. All plans were normalized so that at least 95% of PTV receives the prescription dose and 99% of PTV receives at least 90% of the prescription dose. The high‐dose spillage was defined by the ratio of the volume of all tissue outside the PTV receiving a dose larger than 105% of the prescription dose to the PTV, and the intermediate‐dose spillage was evaluated by the mean dose at the 3mm shell distanced at 2 cm away from the PTV surface. Results: The CIs are much lower for 0 or 2 mm BM than those of 4 mm BM for all patient plans while for two patients, slightly higher for 0 mm BM than those for 2 BM. The high‐dose spillages were on average about 7% lower for 0 or 2 mm BM than those of 4 mm BM for all patient plans while for three patients, higher for 0 mm BM than those of 2 mm BM. The intermediate‐dose spillages were lower for 0 or 2mm BM than those of 4 mm BM. Conclusion: With assumption that PTV fully covers the microscopic disease, tumor motion and setup uncertainty, and following recent ASTRO/ACR guideline that every effort should be made to minimize the volume of surrounding normal tissues exposed to high dose levels, 3D conformal lung cancer SBRT plans appear superior with 2 mm BM or less depending on the tumor location, size and patient geometry.
SU‐GG‐T‐548: Energy and Spatial Distribution of Photon Fluence Emanating from the Head during Stereotactic Radiosurgery for Age‐Related Macular Degeneration
Authors: Hanlon J , Chell E , Firpo M , Bolch W
Published: August 2010

Purpose: Kilovoltage stereotactic radiosurgery (SRS) is currently being explored as a treatment option for wet age‐related macular degeneration (AMD), a leading cause of vision loss in the United States. An evaluation of the distribution of photons exiting the head during treatment will be useful in determining safety parameters regarding clinical staff present. Method and Materials: A male reference head phantom was computationally modeled with Rhinoceros 4.0 using CT slice segmentation scaled to ICRP Publication 89 reference values. The head phantom was voxelized and a three‐beam photon treatment (100 kVp) was modeled using the MCNPX radiation transport code. The beams enter through the sciera at a 30° polar angle relative to the geometric axis of the eye, and deliver a cumulative therapeutic dose of 24 Gy to the macula (8 Gy per beam). An F1 tally sphere, with its origin at the macula target and normal vector aligned with the geometric axis, was used to evaluate the energy and angular distributions of photon fluence at a radius of 0.5 meters. Two‐dimensional matrices were implemented using type 1 mesh tallies, flush with the head tissue, which were used to characterize the spatial distribution of photons emanating from each side of the model. Results: Photon fluence was mostly forward directed with respect to the patient's gaze (backscattered in reference to beam entry) with maxima in the 50–60° and 44.4–50 keV bins. A portion of the beam traverses through the head unattenuated, resulting in a smaller peak around 150°. Color coded contour fluence maps will be created from the mesh tallies to supply a visual representation of fluence. Conclusion: The results of this study will contribute towards the design development of safety parameters related to the treatment device. This work was sponsored by Oraya Therapeutics.
SU‐GG‐T‐549: Development of Respiration Verification Program and Procedure for 4‐Dimensional Stereotactic Body Radiation Therapy
Authors: Shin E , Han Y , Kim J , Lee H , Shin J , Ju S , Lee J , Ahn J , Lee J , Choi D
Published: August 2010

Purpose: In order to verify the behavior of tumor motion caused by breathing, respiration & tumor motion verification procedure was designed and its feasibility was tested. Method and Materials: Visual software was developed using LabView 7.0 to analyze respiration by detecting peak/valley points from RPM signals. The software displays the number of detected peaks/valleys, peak/valley locations, amplitude of signals, and 2nd order differential coefficients at each data points. It calculates mean, standard deviation, variance, maximum and minimum of all detected peak/valley points. It can analyze data for user defined intervals and exports the results in excel file. The program performance was tested using known RPM signals which were sine waves with period of 3 and 6 sec with amplitude of 1 and 2 cm. Also irregular signals obtained from patient's breathing were used to generate irregular respiratory signals by moving a phantom and the software performance was tested. In clinical application, the analyzed respiratory data were converted into tumor motion by applying scaling factor defined by tumor‐motion amplitude to respiration amplitude. To determine the scaling factor, gated On‐Board‐Image (OBI)s were acquired at 0% and 50% of respiratory phases and the imaging times were recorded. From the RPM file, the respiratory signal values at imaging times were read and displacement of tumor was measured from the OBI images. The scaling factor was, then, determined as the ratio of tumor displacement between 0% and 50% phases to difference of two respiratory signals values at corresponding phases. Results: The computed results by the software were extremely consistent with true values within 0.1% difference for regular and irregular motions. Conclusion: Developed software was proven to have sufficient accuracy for clinical application. The proposed method has advantages of non‐invasive, fine temporal resolution without extra radiation, thereby providing a useful tool for 4‐dimensional body stereotactic radiotherapy.
SU‐GG‐T‐550: Small Field Dosimetry for Stereotactic Body Radiotherapy (SBRT)
Authors: Yang J , Wu G , Wagner H , Saw C
Published: August 2010

Purpose: The dosimetry of small radiation field (≤3×3 cm2) poses a number of challenges that includes the nonequilibrium condition and the high dose gradients in a very small region, especially for small field SBRT where high doses are delivered in small number of fractions. The purpose of this work is to assess the dosimetry of small fields, dose accuracy and then verifying SBRT plans using Gafchromic film measurement and Monte Carlo calculations. Materials and Methods: Eclipse planning system was configured with measured data as small as 1×1 cm2 field size. Some small field profiles from planning system at different depths were compared with Gafchromic film measurements and Monte Carlo simulations. Different small field point doses were calculated and compared with measured results and Monte Carlo calculations. Several SBRT small field plans were verified by using films and Monte Carlo simulations based on isocenter dose, target dose coverage, dose volume histogram and critical structure dose distributions. Results: The film measured profiles and point dose for small fields were in good agreement with Eclipse planning system and Monte Carlo simulations within 2mm or 2%. Four small field SBRT plans on lung, brain and liver cancer were selected for evaluation. The target dose coverage and dose distributions from plan, film measurement and Monte Carlo were matched with each other. The isocenter dose difference between Eclipse and Monte Carlo calculation was less than 2%. The dose differences between Eclipse and film measurement were within 4% for all the plans. There was no significant different on critical structures dose distribution for planning system, measurement and Monte Carlo simulations. Conclusion: The application of evaluation techniques as applied in Gamma Knife such as Gafchomic film and Monte Carlo calculations to the dosimetry of very small fields gives better dose accuracies, then sufficient accuracy for small field SBRT.
SU‐GG‐T‐556: Investigations into Treatment Planning for Mycosis Fungoides Localized to the Face
Authors: Fox C , Matuszak M , Fraass B , Moran J
Published: August 2010

Purpose: This work describes an investigation of the best treatment approach to ensure delivery of the desired dose to a patient with extensive mycosis fungoides nodules localized to the face. Method and Materials: The physician's treatment goal was to deliver a uniform dose to the patient's entire face to a depth of 5mm. Several treatment methodologies were considered including a partial total skin electron treatment or patched electron beams. Three different electron treatments were evaluated to determine the best approach. Dose distributions were evaluated at multiple axial slices in an anthropomorphic head phantom. TLDs were placed at points of interest to measure the surface dose. Additional treatment considerations addressed include methods to reduce the dose to the posterior region of the scalp, the nose, the ear canals, the oral mucosa, and the lens, as well as the ability of the therapists to reliably deliver the plan to minimize the risk of variances. Results: The technique that provided the most homogeneous dose utilized five 25×25cm2 electron beams spaced at 60° gantry angles about the patient's head. With this technique the use of oblique beams was an advantage because the depth of dose maximum was raised towards the skin surface. Measurements confirmed the treatment planning algorithms ability to accurately calculate the dose. The use of an immobilization mask reduced patient setup time, further reduced dmax, and permitted use of a single image to verify patient position. In vivo TLD measurements showed a surface dose distribution of ±18%, which is comparable to TSET. Conclusion: Pre‐treatment dosimetry and involvement of the entire treatment team in the planning process allowed for the confident delivery of an atypical course of radiation therapy without incident. The patient responded as desired and in vivo measurements provided feedback for decisions made by the physician over the course of treatment.
SU‐GG‐T‐568: The Effect of Change in Target Volume and Tissue Heterogenity on Dose Distributions during the Course of Treatment with Intensity Modulated Proton Radiotherapy
Authors: Arjomandy B , Yu Z , Dong L , Frank S
Published: August 2010

Purpose: To investigate the changes in dose distribution due to changes in tissue heterogeneity during the course of treatment with intensity modulated proton radiotherapy (TMPT). Method and materials: A retrorespective study was conducted using CT images acquired from daily CT‐guided IMRT treatments for cancer of paranasal sinus. IMPT planning from the Eclipse treatment planning system (Varian Medical Systems) was used to design and calculate the dose distribution and to evaluate the dose volume histograms of GTV, CTV, PTV, and OAR for the first and consecutive daily CT images acquired on a CT‐on‐rails system. Two‐beam optimization was performed on the acquired CT image for the first day of treatment. A verification plan was calculated on subsequent daily CT images by using the same beams' orientation with the same number of beam spots and fluence patterns as used for the first day. Results: The reduction in volume from the first to last day of treatment for GTV, CTV, and PTV were 5%, 1%, and 1%, respectively. The volumetric coverage of GTV, CTV and PTV by 95% isodose line distribution were reduced by 13%, 6%, and 7%, respectively for the same period. The total dose received by 95% of the GTV, CTV, and PTV volume was reduced by 1.5%, 3%, and 5%, respectively. The maximum dose received by brainstem was actually reduced by 52%. Conclusion: Small volumetric changes in tissue heterogeneity will have a diverse effect on tumor coverage for intensity modulated proton radiotherapy. The heterogeneity changes within the target volume affect the range of individual proton pencil beams that collectively optimize the tumor coverage.
SU‐GG‐T‐570: Selection of CT Image Sets for Treatment Planning in Stereotactic Body Radiation Therapy of Lung Cancer
Authors: Wu J , Betzing C , He T , Srisuthep A , Fuss M
Published: August 2010

Purpose: This study investigated the impact on tumor dose coverage of treatment plans performed on various CT image sets in stereotactic body radiation therapy (SBRT) of lung cancer. Methods and Materials: Five patients underwent SBRT for lung cancers were retrospectively investigated. For each patient, a free breathing (FB) CT and a four‐dimensional (4D) CT were acquired. Based on the 4DCT scans, two post‐processing CT images were reconstructed: average intensity projection CT (AIP) and a low pitch, slow‐scan CT (SCT). The gross target volumes (GTVs) were delineated on the 4DCT images and combined to create the internal target volume (ITV). The planning target volume (PTV) was created by adding a 5 mm margin to the ITV. Treatment plans were performed on the FB CT, ATP CT, and SCT. Plan quality was evaluated by calculating and comparing the 4D dose for each plan using deformable‐image registration. Results: No matter which CT image sets were used in treatment planning, lung tumors always receive at least the prescribed dose. The average difference in tumor D100 (minimum dose received by 100% of the tumor) is 0.28±0.61Gy (p=0.363) between the plans performed on AIP CT and those on FB CT, 0.62±1.35Gy (p=0.379) between the plans performed on AIP CT and those on SCT, and 0.34±0.77Gy (p=0.379) between the plans performed on FB CT and those on SCT. As for the mean lung dose, the average difference is −0.07±0.15Gy (p=0.390), 0.07±0.11Gy (p=0.221), and 0.14±0.15Gy (p=0.107) respectively. For the total lung V20, the average difference is −0.19±0.26% (p=0.186), 0.13±0.25% (p=0.321), and 0.31±0.27% (p=0.06) respectively. Conclusions: The differences in tumor and lung dose coverage for treatment plans performed on ATP CT, FB CT and SCT are indistinguishable. Those three CT data sets are equally well in term of dose coverage for treatment planning in lung SBRT.
SU‐HH‐BRB‐09: Real‐Time Soft‐Tissue Imaging Concurrent with External Beam Radiation Therapy Delivery
Authors: Schlosser J , Salisbury JK , Jeffrey RB , Hristov D
Published: August 2010

Purpose: The challenge of real‐time visualization, localization, and tracking of organ motion and deformation concurrently with external beam radiation therapy (EBRT) delivery remains unmet and unattainable by existing image guidance technologies. We propose to address this challenge in the development of a novel, minimally interfering, robotic ultrasound image guidance system that can be integrated with existing medical linear accelerators. Method and Materials: The span of ultrasound transducer motion required for trans‐abdominal prostate imaging was quantified via optical tracking of a probe during free‐hand acquisitions. This information was incorporated into the design of a customized human‐safe robotic manipulator to remotely control the transducer position and pressure while avoiding LINAC gantry collisions. The effect of accelerator‐induced electromagnetic interference on the robot was investigated. In addition, a treatment plan with beam directions restricted to sectors that do not interfere with the ultrasound transducer was evaluated. Results: Prostate image integrity was sensitive to probe pitch, thus the manipulator was designed to actively control abdominal pressure (0–10N) and transducer pitch (−40°−90°). Probe placement in other directions remains adjustable to accommodate anatomy variations. Human‐safety requirements translated into the design via a torque limiting friction clutch, lightweight backdriveable links, and remote center of motion pitch mechanism. Collision avoidance was confirmed by rotating the gantry 360° around the robot mounted on the LINAC couch in a typical treatment setup. The control system of the robot behaved similarly with the LINAC beam off and on, with mean servo cycle intervals of 1000.03 μs and 1000.06μs, respectively. For a representative prostate setup, remotely‐controlled robotic ultrasound image acquisition was successfully demonstrated on a volunteer. Dose volume histogram (DVH) for an IMRT plan with restricted sectors remained virtually identical to a clinically employed DVH. Conclusion: Remotely‐controlled robotic ultrasound imaging is feasible and may offer real‐time intra‐fractional soft‐tissue guidance concurrent with EBRT delivery.
SU‐HH‐BRB‐10: Adaptive Seasonal Autoregressive Model Based Intrafractional Lung Tumor Motion Prediction for Continuously Irradiation
Authors: Ichiji K , Sakai M , Homma N , Takai Y , Yoshizawa M
Published: August 2010

Purpose: To irradiate continuously to a moving tumor, core techniques are to observe position and shape of the target tumor and to adapt the radiation beam to the intra‐fractional motion and deformation. In addition, we need a compensation technique because measurement of the tumor position and control of the radiation device have some time delays. In this study, we propose a new prediction method of lung tumor motion, to compensate the time delays. Method and Materials: An essential core of the proposed method is adaptation to time‐variant nature of lung tumor motion. Lung tumor motion observed at Hokkaido university hospital was used for development of the proposed method. The motion has time‐variant, but periodic nature, that is, the cyclic period changes with time. This nature often causes the rise of the prediction error when we use conventional prediction method for periodical time series (e.g. seasonal autoregressive integral moving‐average model: SARIMA). The proposed method is based on SARIMA model, but was developed to take into account the quasi‐periodic nature of the lung tumor motion. To estimate the time‐variant period, we adopted correlation analysis. Then, the conventional SARIMA model was modified to a time‐variant SARIMA model by using the estimated period. Results: Prediction error of the proposed method was compared with that of the conventional methods, by using real lung tumor motion. Experimental results show that the prediction error of the proposed method was the least. The average of prediction error are 0.7911 [mm] at 0.5[sec] ahead and 0.8818[mm] at 1.0[sec] ahead, respectively. Conclusion: We have developed the new prediction method of the lung tumor motion for compensation of time‐delays of radiation device. The proposed method achieved highly accurate prediction of the real lung tumor motion. The method can thus sufficient for continuously irradiation to the moving lung tumor.
SU‐HH‐BRB‐11: Range Adaptive Proton Therapy for Prostate Cancer
Authors: Melancon A , Lee A , Kudchadker R , Titt U , Beddar S , Zhu X , Dong L
Published: August 2010

Purpose: The rapid distal falloff of a proton beam allows for sparing of normal tissues distal to target organs. However proton beams that aim directly towards critical structures are avoided due to concerns of range uncertainties, such as CT number conversion and anatomy variations. We propose to eliminate range uncertainty and enable prostate treatment with a single anterior beam by detecting the proton's range at the prostate‐rectal interface and adaptively adjusting the range in vivo and in real‐time. Materials and Methods: A prototype device, consisting of an endorectal liquid scintillation detector and dual‐inverted lucite wedges for range compensation, was designed to test the feasibility and accuracy of the technique. Liquid scintillation filled volume was fitted with optical fiber and placed inside the rectum of an anthropomorphic pelvic phantom. Photodiode‐generated current signal was generated as a function of proton beam depth, and the spatial resolution of this technique was calculated by relating the variance in detecting proton spills to the penetration depth. The relative water‐equivalent thickness of the wedges was measured in a water phantom and prospectively tested to determine the accuracy of range corrections. Treatment simulation studies were performed to test the potential dosimetric benefit in sparing the rectum.Results: The spatial resolution of the detector in phantom measurement was 0.5 mm. The precision of the range correction was 0.04 mm. The residual margin to ensure CTV coverage was 1.1 mm. The composite distal margin for 95% treatment confidence was 2.4 mm. Planning studies based on a previously estimated 2mm margin on 27 patients showed a rectal sparing up to 51% at 70Gy and 57% at 40Gy relative to IMRT and bilateral proton treatment. Conclusion: We demonstrated the feasibility of our design. Use of this technique allows for proton treatment using a single anterior beam, significantly reducing the rectal dose.