bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐193: Using Truebeam's Research Mode to Automate Mechanical Quality Assurance
Authors: Grantham K , Rangaraj D , Santanam L
Published: June 2012

Purpose: To determine the feasibility of automating mechanical quality assurance measurements on the Varian Truebeam LINAC. Methods: Using the XML coding capability of the Varian Truebeam Research Mode, the LINAC was programmed to mimic the beams delivered for the following mechanical tests. These tests included: Field size accuracy, jaw positions for asymmetric fields, collimator rotation isocenter, and MLC positional‐accuracy. Images for these beams were acquired with the EPID. The images were analyzed using an analysis code written in MATLAB. Tests for gantry and couch rotation isocenters and radiation and mechanical isocenter coincidence are being developed. Results: For field‐sizes ranging from 4×4cm2 to 15×15cm2, the measured matched the nominal field sizes to within 1mm. The collimator rotation isocenter and the overall accuracy for asymmetric field matched to within 1mm. No positional error 〉1mm was seen in the 33 MLC pairs visible in the MLC positional‐accuracy images. Conclusions: A large portion of the time required to make mechanical QA measurements using film is spent placing, processing, and scanning the film. Complete automation in performing these mechanical tests results in a significant time gain compared to film. A majority of the mechanical tests suggested by TG‐142 have been performed using this technique, and an automated mechanical QA process has been established in our clinic.
SU‐E‐T‐194: Evaluation and Simulation of Shallow Depth Skin Dose from Couch Top in Radiotherapy
Authors: Li K , Able A , Newton J , Cornell D
Published: June 2012

Purpose: When the treatment couch‐top contacts the patient, the skin dose to the patient also generates clinical significance as the radiation beam passes through the couch. In this study, the effect on entrance shallow depth dose was investigated for the carbon fiber exact couch‐top from Varian Medical System. Methods: An Accredited Dosimetry Calibration Laboratory (ADCL) calibrated PTW parallel‐plate thin‐window chamber was used to measure the doses in the build‐up region. Firstly, the shallow depth doses at different field sizes, depths and incident angle beams were measured for 6MV and 18MV photon beams. To test the couch top contribution to the dose distribution, the depth of measurement went down to 10cm. The couch was simulated in the Eclipse treatment planning system and the related point dose was calculated with different depths. The CT number of the couch top was adjusted to generate agreement between measurement and simulation. Results: At a 2mm depth, the surface dose increased with the decrease of the field size. Comparing with and without the couch top, as field sizes vary from 20cm×20cm to 2cm×2cm, the dose increased from 35% to 53% of for 6MV, and from 50% to 113% for 18MV. At 0mm depth, the dose difference was most significant and is at the level of 300%. Angle incident beam dose increase due to couch top varied with complicated dose distribution. Extended Depth Dose measurement shows that couch top effect on dose in build‐up region extends to depths of 1cm for 6MV and 2cm for 18MV. An appropriate CT number setting of the couch top is between −200HU to −300HU. Conclusions: The couch simulation in Eclipse displays better dosimetric accuracy in couch contacted skin dose. However, calculation factors such as surface definition, heterogeneity, calculation resolution and algorithm also need extra consideration.
SU‐E‐T‐203: Development of a QA Software Tool for Automatic Verification of Plan Data Transfer and Delivery
Authors: Chen G , Li X
Published: June 2012

Purpose: Consistency verification between the data from treatment planning system (TPS), record and verification system (R&V), and delivered recorder with visual inspection is time consuming and subject to human error. The purpose of this work is to develop a software tool to automatically perform such verifications. Methods: Using Microsoft visual C++, a quality assurance (QA) tool was developed to (1) read plan data including gantry/collimator/couch parameters, multi‐leaf‐collimator leaf positions, and monitor unit (MU) numbers from a TPS (Xio, CMS/Elekta, or RealART, Prowess) via RTP link or DICOM transfer, (2) retrieve imported (prior to delivery) and recorded (after delivery) data from a R&V system (Mosaiq, Elekta) with open database connectivity, calculate MU independently based on the DICOM plan data using a modified Clarkson integration algorithm, and (4) compare all the extracted data to identify possible discrepancy between TPS and R&V, and R&V and delivery. Results: The tool was tested for 20 patients with 3DCRT and IMRT plans from regular and the online adaptive radiotherapy treatments. It was capable of automatically detecting any inconsistency between the beam data from the TPS and the data stored in the R&V system with an independent MU check and any significant treatment delivery deviation from the plan within a few seconds. With this tool being used prior to and after the delivery as an essential QA step, our clinical online adaptive re‐planning process can be speeded up to save a few minutes by eliminating the tedious visual inspection. Conclusions: A QA software tool has been developed to automatically verify the treatment data consistency from delivery back to plan and to identify discrepancy in MU calculations between the TPS and the secondary MU check. This tool speeds up clinical QA process and eliminating human errors from visual inspection, thus improves safety.
SU‐E‐T‐213: Development of a Web Wrapper to Facilitate Radiotherapy Research
Authors: Folkerts M , Graves Y , Gautier Q , Kim G , Jia X , Jiang S
Published: June 2012

Purpose: Researchers write many computer programs with unique implementations, usually requiring a great amount of effort for other researchers to learn how to install, configure, and use. Some programs require specialized hardware platforms such as GPU workstation or CPU cluster, which may not readily available for many researchers. This work develops a general web platform to ‘wrap’ radiotherapy software tools into a user friendly, browser‐based interface. Methods: We developed a web wrapper based on existing technologies (e.g. HTML5, JavaScript, PHP, Python, XML) to interface with command line‐based research tools. This wrapper enables users to easily perform various tasks in any modern web browser, while underlying tools are launched remotely. Visitors can upload data, configure settings, process data remotely, then view, share, and download results with minimal effort. This web wrapper is developer friendly; new tools are easily integrated by editing XML configuration files. Results: As a test case, we have successfully wrapped a set of command line tools, developed by our group, into a single web app, providing fluence map generation, CT image processing, and GPU‐based Monte Carlo (MC) dose calculation. The result is a web‐based quality assurance tool. With this tool, users can upload compressed DICOM‐RT files, recompute dose using the MC method, and evaluate the results by viewing dose distribution, 3D gamma index distribution and DVH curves. The entire work‐flow can be completed within 2 minutes provided users have a reasonable Internet connection speed. Conclusions: We have developed an web wrapper to increase the accessibility of radiotherapy tools and reduce users' learning curve through a friendly web‐based interface. This work also allows quick and easy deployment and distribution of software tools developed by researchers to the whole community.
SU‐E‐T‐218: The IHE‐RO Helper Tool: Demonstrating the Connectivity Issues Solved by IHE‐RO
Authors: Kapoor Rishabh , Yeung Daniel , Kumar Sabari Ajay , Alex Daley , Kapur Priyanka , Palta Jatinder
Published: June 2012

Purpose: To develop a Web‐based application (IHE‐RO Helper) to allow comprehensive review of the interconnectivity and interoperability of various radiotherapy devices established through testing sanctioned by the Integrating Healthcare Enterprise‐Radiation Oncology (IHE‐RO).Material and Methods: IHE‐RO is an initiative sponsored by ASTRO to improve the way computer based systems in radiation oncology share information using well‐defined data exchange standards (DICOM / HL7). At the IHE‐RO Connectathon events over the last 4 years, 11 vendors with 14 different products have successfully tested and identified solutions to connectivity problems in treatment planning, simulation and delivery. Because the test results are highly technical, the interconnectivity issues amongst the RT devices may get overlooked by the end users. The IHE‐RO helper tool is designed to operate in simple clinical terms with queries and presentations organized based on treatment techniques and clinical features that are familiar to the practitioners. For example, if you are planning to purchase a treatment planning system capable of generating plans (e.g. Stereotactic treatments) and are concerned whether the TPS can successfully transfer such data to your treatment management system (TMS) and subsequently to your treatment delivery system (TDS), the IHE‐RO Helper can identify the connectivity requirements and list vendors that have successfully passed an IHE‐RO Connectathon and validated their solution to the specific requirements. Results: The IHE‐RO helper tool provides a graphical and textual user interface to effectively demonstrate the solved interconnectivity problems between TPS, TMS and TDS. A report is also provided that explains the interconnectivity problems and its solutions. Conclusions: The IHE‐RO helper is an effective tool to clearly identify vendor products that are IHE‐RO compliant, thereby encourages vendor participation in testing and validation. Such a tool will be invaluable in procurement of new equipment to ensure a priori interoperability with anticipated RT devices deployed in the clinic. This research and development project is supported by the Bankhead‐Coley Cancer Research Program grant # RC1‐09BW‐09‐26833
SU‐E‐T‐226: Clinical Implementation of a Gravity‐Oriented Wedge for Total Body Irradiation
Authors: Koch N , Yount C , Prado K , Nelson S , Jenrette J , Vanek K
Published: June 2012

Purpose: To describe a TBI technique designed within the limits of a small‐room geometry and its clinical implementation. Methods: Following construction of the universal treatment devices, including the double‐wedge, beam spoiler table, and patient support table, commissioning consists of measurements to determine the output, tissue‐phantom ratio, effective source distance, and off‐axis factor. Dose is calculated by applying these factors per patient‐specific measurements to arbitrary point in the patient. Typically, ten calculation points are located at mid‐separation along the mid‐sagittal plane from the head to the ankles. When areas of unacceptably high dose are calculated, custom compensators are constructed from 5‐mm sheets of PMMA and placed over the patient on top of the beam spoiler table. The typical dose homogeneity of the planning calculations is within 2% of the prescribed dose. Results: To verify the accuracy of the technique, an anthropomorphic phantom was simulated and treated. In total, 128 thermoluminescent dosimeters (TLDs) were irradiated within the phantom. Concentrations of TLDs were located in the planes of selected calculation points, i.e. the head, neck, sternum, lung, umbilicus, and pelvis. Results showed the average dose to these locations differed from the intended dose by −3.5%, 3.4%, 2.6%, 9.5%, 2.8%, and 0.5%, respectively. Due to its heterogeneous material, a higher discrepancy in the lung dose was anticipated. To demonstrate the dosimetric size of the radiation field, ionization chamber measurements were taken on one lateral side of the treatment area at a constant depth of 5 cm. A few measurements on the contralateral side were within 1 %, verifying the field's lateral symmetry. The approximate treatment area for the current technique is approximately 180×50 cm. Conclusions: We have demonstrated a small‐room technique capable of meeting the dosimetric goal of TBI. To improve the dosimetric characteristics, new universal treatment devices are currently being designed and constructed.
SU‐E‐T‐227: Re‐Evaluation of Dose Distribution and Margins for IMRT Prostate Plans
Authors: He W , Wei X , Hsieh H , Harvey A , Chen W
Published: June 2012

Purpose: To evaluate the dose distribution on prostate and proximal seminal vesicles (SVs), rectum, and bladder when a certain geometry uncertainty is occurred during planning or delivery, and further determine the optimistic margin relation to different directions. Methods: Thirty prostate cancer patients with prostate specific antigen (PSA) less than 10 and Gleason Score between 2 and 6 have been selected and planned in EclipseTM 10.0 treatment planning system. PTV is expanded from GTV (prostate plus proximal SVs) with uniform 6 mm margin in all directions. All patients are head‐first‐supine and planned with seven beam IMRT technique. At least 95% of PTV is covered by full prescription. Rectum V65 is less than 17%, rectum V40 is less than 35%, bladder V65 is less than 25%, and bladder V40 is less than 50%. To simulate the deviation from planning error or setup uncertainty, the original isocenter of each plan has been shifted every 2mm from 0mm to 10mm in superior (S), inferior (I), right (R), left (L), anterior (A), and posterior (P) directions. The dose is then re‐calculated with fixed jaw technique. The new plan parameters such as PTV coverage, both bladder and rectum V65 and V40 are analyzed. Results: PTV full dose coverage is linearly decreasing with increasing isocenter shift and the absolute slope mean values are 2.2, 2.2, 3.0, 2.7, 2.0, and 2.0 corresponding to S‐I‐P‐A‐L‐R directions. As for rectum and bladder, the further away from the shifted isocenter, the smaller values of V65 and V40. Conclusions: This study shows that 2 to 3 percentage of decrements on PTV full dose coverage occurs while prostate target shifts every millimeter. To uniformly cover the dosimetric impact uncertainty, it shows that the optimistic margin ratio would be 1.1(S):1.1(I):1.5(P):1.35(A):1(L):1(R) for the six directions
SU‐E‐T‐229: Monte Carlo Dosimetric Study of SAVI HDR Applicator for Partial Breast Irradiation
Authors: Zhang Zhengdong , Dou Kai
Published: June 2012

Purpose: To investigate the dosimetric variation by Monte Carlo and experimentally simulating the situation with and without tissue invagination and the potential translation and rotation of the SAVI applicator for partial breast irradiation. Methods: The SAVI applicator with the cavity filled with air and water was merged into a water phantom and the delivered dose was simulated by MCNP monte carlo program. The results verified using an ion chamber and film were compared with a homogenous dose calculation by the treatment planning system. A dose variation from the SAVI translational shift was simulated and measured by moving an ion chamber along with the central axis direction. A dose change from the SAVI rotation was simulated and measured by placing an ion chamber at a fixed point while rotating the SAVI device about the central axis. Results: The dosimetric variations for the SAVI device were found to be related to the cavity dimension, source arrangement, and dwell times. For the single dwell source placed in the center of the applicator, the maximum difference of the dose with the air cavity at 1cm away from the air‐water boundary is about 7% higher than that with water filling in the cavity. But the simulation and measurements with nearly fully loaded multi‐sources for the same situation show a difference of less than 3%. The 3% dose variation in average was found from either the 3 mm translation or 3 degree rotation of the SAVI applicator. Conclusions: The maximum dosimetric effect of an air cavity is 7% off compared with a water filled cavity when a single dwell source position is used in the center of the central catheter. Multiple catheters of the SAVI applicator with a nearly fully loaded dwell source position produce the discrepancy of less than 3% and allow for optimal and conformal dose distribution to a lumpectomy cavity while minimizing the dose to adjacent normal structures.
SU‐E‐T‐232: Proton Source Modeling for Geant4 Monte Carlo Simulations
Authors: Barnes S , McAuley G , Wroe A , Slater J
Published: June 2012

Purpose: To investigate the effect of initial proton beam source placement, distribution and angle on the proton dose distribution in a therapeutic nozzle using Geant4. Methods: We performed Geant4 Monte Carlo simulations of a passively scattered proton treatment nozzle. Accurate geometry including all elements in the treatment room was used. Protons were generated just inside the vacuum pipe using one of two models. First, a standard two dimensional Gaussian distribution of proton starting position was used with a small random angle added to the initial direction. The size of the Gaussian distribution and the random angle were set to match measured beam spot size and angular spread at the exit window. Second, a point source of protons further back in the vacuum pipe with a small random angle was used. The distance of the point source to exit window and the random angle were set to match the spot size and angular deviation used for the Gaussian distribution. Depth dose curves and orthogonal beam profiles were examined to determine changes between the two models. Results: Orthogonal beam profiles for large apertures showed changes of up to 6.5% between the two models with the point source showing much better agreement with measured data. Depth dose curves and orthogonal profiles for small apertures were unaffected. For large apertures, the average difference compared to measured data was of 1.9% and 0.7% and the max difference was 5.0% and 1.6% for Gaussian and point sources, respectively. Conclusions: The point source more realistically models the proton distribution in the vacuum pipe by correlating the proton position with the direction. For certain scattering setups and large apertures point source modeling is necessary to accurate match measured data with Monte Carlo simulations.
SU‐E‐T‐236: Brachytherapy for Breast Cancer Patients with Implanted Pacemeker, Using Multi Lumen Partial Breast Applicator
Authors: Jacob D , Strasser J
Published: June 2012

Purpose: Discuss optimised Accelerated Partial Breast Irradiation (APBI) using a Strut‐Adjused Volume Implant (SAVI) applicator for patients with implanted pacemeker, without overdosing or relocating the pacemaker. Methods: A right breast cancer patient with an in situ pacemaker (Medtronic model ADDR01) on the right side underwent breast conservative surgery and was referred for Partial Breast Irradiation (PBI) using Ir‐192 High Dose Rate Brachytherapy. Preliminary estimation of the pacemaker dose from a pre‐insertion CT study was about 8 % of the prescribed dose which exceeded the generally accepted dose of 2Gy. The challenge was to use a suitable applicator to treat the tumor bed and 1cm margin without exceeding the 2Gy limit to the pacemaker and the leads. A seven catheter SAVI device was selected and implanted in the right breast in an optimal direction and a 3D treatment plan was generated following a post insertion CT scan, using the Oncentra Brachy treatment planning system. Optimization tools namely anatomy based Inverse Planning Simulated Annealing (IPSA), and graphical optimization were utilized to load and optimize the dwell time in the catheters and reduce the dose received by the pacemaker. Device interrogation was conducted before and after the treatment. All operational parameters of the pacemaker were found to be normal.No change in the baseline reference values were observed. Results: Using the SAVI device it was possible to limit the pacemaker/ leads dose to less than 2 Gy. Target V100, V95 and V90 were 90.1%, 95.5% and 98.5% respectively. V150 and V200 being 18.6cc and 10.6cc respectively.Calculated average point doses on pacemaker assembly for ten fractions was 140cGy. Conclusions: By combining the optimization tools of today's Brachytherapy planning system and a multilumen SAVI applicator, HDR partial breast irradiation can be safely delivered for breast cancer patients with in situ pacemaker, with out the fear of interrupting pacemaker functionality
SU‐E‐T‐244: High Spatial Resolution EBT2 Film Dosimetry
Authors: Poppinga D , Schoenfeld A , Poppe B , Chofor N
Published: June 2012

Purpose: The purpose of this study was to measure depth dose curves and dose effects near high‐Z interfaces with radiochromic EBT‐2 films reaching a spatial resolution superior to conventional methods with no quality losses. Methods: The setup is made of two 12cm stacks of RW3, fixing an EBT2 film in a vertical position. To measure a depth dose curve, the setup was irradiated with a 15MV photon beam (Siemens Primus). Since the film is positioned parallel to the beam propagation, the depth dose curve is measured with only one film per depth. Additionally, a dental gold alloy probe was inserted in the RW3 stack at 6cm depth and the dose enhancement in front of the probe was measured with the method described above. Hereby, the bottom edge of the film touches the probe's surface.The irradiated films were digitized with a resolution of 72dpi using an Epson 10000XL flatbed scanner with a transparency unit and alignment frames. With this setup, the spatial resolution is only limited by the scanning resolution. Results: In order to verify the new measurement method, comparisons of the measured depth dose curves with the conventional method of placing the film orthogonal to the beam propagation showed deviations of lesser than 3%.The comparison of the dental gold measurements with Monte Carlo simulations shows a systematic lower measured dose which is still within 5% consistency. However attention has to be paid in the experimental setup and film preparation. Conclusions: The introduced method shows significant advantages to conventional orthogonal EBT2 film positioning. It shows a very high spatial resolution and the area of interest is only limited by the film size. The method will be used in further studies, to investigate dose profiles and dose effects near interfaces and in inhomogeneities.
SU‐E‐T‐252: Consolidating Duodenal/Small Bowel Toxicity Data via Iso‐Effective Dose Calculations Based on Compiled Clinical Data
Authors: Prior P , Tai A , Erickson B , Li X
Published: June 2012

Purpose: To consolidate duodenal toxicity data from clinical studies with different dose fractionation schemes using the modified linear quadratic (MLQ) model. A methodology of adjusting the dose‐volume parameters todifferent levels of normal tissue complication probability (NTCP) was proposed and used to estimate dose‐volume constrains for treatment planning. Methods: A set of modified Lyman model parameters for duodenum NTCP were estimated by the chi‐squared fitting method using tolerance dose and equivalent uniform dose (EUD) data obtained in a literature search. These model parameters were then used to convert the dose‐volume pair, (D, V) to the iso‐effective dose (in 2 Gy per fraction)‐ volume pair, (DMLQED2, V). A relationship was derived to convert a given DMLQED2 at one level of NTCP, to an iso‐effective dose at another NTCP. Results: The literature search yielded six reports useful in making estimates of small bowel/duodenal toxicity. The modified Lyman model parameters were found to be TD50 = 60.9 ± 7.9 Gy, m = 0.21 ± 0.05, and Î = 0.09 ± 0.03 Gy‐1. The toxicity rates associated with hypo‐fractionated radiotherapy (HBRT) were found to be consistent with other clinical data of conventional fractionations found in the literature. The conversion of DMLQED2 between different NTCP levels remains consistent with each other over a narrow range of NTCP. Conclusion: MLQ based iso‐effective calculations of dose‐response data corresponding to Grade > 2 toxicity were found to be consistent with one another within the uncertainty of DMLQED2 due to model parameter uncertainty. The dose‐volume data that can be converted to different NTCP levels may be used to estimate duodenal/small bowel dose‐volume constrains for new dose fractionation and/or dose escalation strategies. Medical College of Wisconsin Cancer Center Meinerz Foundation
SU‐E‐T‐253: Assessing Small‐Volume Cord Biological Effective Dose for Repeat Spinal Stereotactic Body Radiotherapy Treatments
Authors: Ma L , Sahgal A , Kirby N , Larson D
Published: June 2012

Purpose: Small‐volume biologically effective (BED) dose limits are critical to safe spinal stereotactic body radiotherapy (SBRT) delivery. However, due to mismatch in spatial location of dose hot spots from non‐uniform dose distributions inherent to SBRT, for repeat treatment courses they cannot be simply added by assuming a uniform dose distribution. This study aims to develop a probability‐based biological equivalent dose formula to solve this problem. Methods: A generalized biological equivalent dose (gBED) was formulated via computing damaging or survival probability of repeat spine SBRT treatments. Parameters from the linear‐quadratic model such as α/β =2 Gy for the spinal cord were applied for the gBED calculations. The derived method was applied to both simulated and clinical treatment cases to demonstrate its applicability and usefulness for assessing spinal cord dose limits for repeated SBRT treatment courses. Results: The gBED formula allows direct superposition of dose within a small volume of spinal cord from a non‐uniform dose distribution of varying dose fractionation schemes of SBRT. From the studied examples, traditional BED calculations even with full voxel‐by‐voxel tracking calculations resulted in inconsistent BED values and can underestimate the biological dose to a small‐volume spinal cord by as much as 20%. Such an error tends to increase rapidly with increasing volume of interests such as from 0.1 mL to 2.0 mL. Conclusions: When assessing spinal cord tolerance for repeat spinal SBRT treatments, consistent surrogates such as gBED are needed to avoid potential underestimation of treatment‐induced complications.
SU‐E‐T‐254: Quantitative Evaluation of Three Mathematical Models for Radiation‐Induced Secondary Cancer Risk for Lung in Stereotactic Body Radiotherapy
Authors: Han C , Nguyen K , Schultheiss T , Wong J
Published: June 2012

Purpose: Several mathematical models exist to predict secondary cancer risks from radiotherapy treatment. In this study, we aimed to compare three dosimetry‐based models in the application of stereotactic body radiotherapy (SBRT) of early‐stage non‐small cell lung cancer (NSCLC) with three radiotherapy treatment modalities. Methods: Ten patients who received definitive SBRT for early‐stage NSCLC were retrospectively selected. for each patient, a helical tomotherapy (HT) plan, a three‐dimensional conformal radiotherapy (3D‐CRT) plan, and a volumetric modulated arc therapy (VMAT) plan were generated to deliver 50 Gy to the planning target volume in five fractions. The excess absolute risk (EAR) for secondary lung cancer occurrence was calculated using three risk models: the linear‐exponential model, the plateau model, and the linear model. The sensitivity of the EAR to the prescription dose was evaluated by varying the prescription dose in the range of 40 to 60 Gy. Results: Based on the linear‐exponential model, the average EAR's (in occurrences per 10,000 patients per year) were 8.4+/−2.7, 8.3+/−2.1, and 8.4+/−1.9 for the HT plans, 3D‐CRT plans, and VMAT plans respectively with 40 Gy prescription dose, and 9.4+/−2.5, 9.0+/−2.1, and 9.3+/−1.8 with 60 Gy. Based on the plateau model, the average EAR's were 10.7+/−3.9, 10.6+/−3.0, and 10.9+/−2.8 with 40 Gy, and 12.9+/−4.2, 12.6+/−3.4, 12.9+/−3.1 with 60 Gy. Based on the linear model, the average EAR's were 29.1+/−13.4, 29.4+/−11.4, and 30.0+/−11.1 with 40 Gy, and 43.8+/−20.1, 44.0+/−11.0, 45.1+/−16.6 with 60 Gy. The difference in EAR's were not statistically significant among the HT, 3D‐CRT, and VMAT plans. Conclusions: Three secondary cancer risk models, as well as three SBRT treatment modalities, were compared. There was no significant difference in secondary lung cancer risks among the three treatment modalities in this study.
SU‐E‐T‐255: A Novel Rectal Obturator for Prostate Radiotherapy Improves the Spatial Distribution of Dose and Reduces the Predicted Risk for Rectal Bleeding and Subjective Sphincter Control
Authors: Buettner F , Alexander E , McNair H , Bulbrook L , Gulliford S , Partridge M , Dearnaley D
Published: June 2012

Purpose: To investigate the effects of an endorectal device during prostate radiotherapy on the spatial distribution of dose to the ano‐rectal region and quantify implications for normal‐tissue‐complication probabilities. Methods: Twenty‐three patients with localised prostate cancer, referred for external beam radiotherapy had 2 CT scans acquired, without and with the rectal obturator (ProSpare) in‐situ. For each patient two dose distributions were generated, based on both CT scans. Dose‐surface maps for the rectal surface and the anal surface were generated and mean dose as well as a spatial measure (circumference of the dose distribution) were determined for all patients, with and without ProSpare. Using previously published NTCP models, the effect of ProSpare on NTCP was investigated for rectal bleeding and subjective sphincter control. Results: In a previous study subjective sphincter control correlated strongest with mean dose and lateral extent at 53 Gy. The use of ProSpare resulted in a highly significant reduction of the lateral extent at 53 Gy (p=0.006), mean dose (p=0.0009) and NTCP according to the LKB model (p=0.002 for grade 2 and p=0.001 for grade >=1). In a previous study we reported that rectal bleeding correlated most strongly with the lateral extent at 55 Gy and presented the constraint that it should not exceed 42% of the circumference. Using ProSpare resulted in a significant reduction of the lateral extent at 55 Gy (p=0.001) and significantly more patients met that proposed constraint (p=0.047). ProSpare resulted in a significant reduction of NTCP for grade‐2 rectal bleeding (p=0.007) and a reduction for rectal bleeding grade >=1 (p=0.053). Conclusions: ProSpare resulted in a significant reduction of mean dose to the anal sphincter and a significant reduction of the lateral extent at 55 Gy. This corresponded to a significant reduction in the predicted risk of reporting subjective sphincter control and grade‐2 rectal bleeding.
SU‐E‐T‐257: Risk of Radiogenic Second Cancer after Photon and Proton Craniospinal Irradiation
Authors: Zhang R , Howell R , Giebeler A , Taddei P , Mahajan A , Newhauser W
Published: June 2012

Purpose: To compare proton and photon therapies in terms of the risks of second cancers for a pediatric medulloblastoma patient receiving craniospinal irradiation (CSI). Methods: Two CSI treatment plans with 23.4 Gy or Gy (RBE) prescribed dose were computed for a 4‐year‐old boy withmedulloblastoma: a three‐field 6‐MV photon therapy plan and a four‐field proton therapy plan. The primary doses for both plans were determined using a commercial treatment planning system. Stray radiation doses for proton therapy were determined from Monte Carlo simulations, and stray radiation doses for photon therapy were determined from measured data. The dose‐risk model based on Biological Effects of Ionization Radiation VII report was used to estimate risk of second cancer. Results: Baseline predictions of the relative risk of each organ were always less for proton CSI than for photon CSI after various follow‐up years for the patient. The lifetime risks of the incidence of second cancer after proton CSI and photon CSI were 7.7% and 92%, respectively, and the ratio of lifetime risk was 0.083. Uncertainty analysis revealed the qualitative findings of this study were insensitive to any plausible changes of dose‐risk models and mean neutron radiation weighting factor. Conclusions: Proton therapy confers lower predicted risk of second cancer for the pediatric medulloblastoma patient compared with photon therapy.
SU‐E‐T‐259: A Statistical and Machine Learning‐Based Tool for Modeling and Visualization of Radiotherapy Treatment Outcomes
Authors: Oh J , Wang Y , Apte A , Deasy J
Published: June 2012

Purpose: Effective radiotherapy outcomes modeling could provide physicians with better understanding of the underlying disease mechanism, enabling to early predict outcomes and ultimately allowing for individualizing treatment for patients at high risk. This requires not only sophisticated statistical methods, but user‐friendly visualization and data analysis tools. Unfortunately, few tools are available to support these requirements in radiotherapy community. Methods: Our group has developed Matlab‐based in‐house software called DREES for statistical modeling of radiotherapy treatment outcomes. We have noticed that advanced machine learning techniques can be used as useful tools for analyzing and modeling the outcomes data. To this end, we have upgraded DREES such that it takes advantage of useful Statistics and Bioinformatics toolboxes in Matlab that provide robust statistical data modeling and analysis methods as well as user‐friendly visualization and graphical interface. Results: Newly added key features include variable selection, discriminant analysis and decision tree for classification, and k‐means and hierarchical clustering functions. Also, existing graphical tools and statistical methods in DREES were replaced with a library of the Matlab toolboxes. We analyzed several radiotherapy outcomes datasets with our tools and showed that these can be effectively used for building normal tissue complication probability (NTCP) and tumor control probability (TCP) models. Conclusions: We have developed an integrated software tool for modeling and visualization of radiotherapy outcomes data within the Matlab programming environment. It is our expectation that this tool could help physicians and scientists better understand the complex mechanism of disease and identify clinical and biological factors related to outcomes.
SU‐E‐T‐260: Radiation Exposure Estimation for 131Cs Prostate Implant Patient Release Determination
Authors: Yang M , Du W , Frank S , Pugh T , Bruno T , Kudchadker R
Published: June 2012

Purpose: Due to the short half‐life and high energy of Cesium‐131 (131Cs), the exposure rate outside the patient could potentially increase radiation exposure to hospital staff and exceed the maximum patient release exposure rate limit. A calculation technique has been developed to estimate the exposure rate at 1 meter from the patient, for prostate patients receiving 131Cs implants. Methods: In our calculation for each patient, all 131Cs sources were treated as one single source, and the point on the prostate with the shortest distance to skin surface was selected as the effective source position. Attenuation inside the patient was calculated based on the attenuation coefficient of 30 keV photons in water, assuming homogeneous patient density. This calculation technique was evaluated on our first 25 131Cs implant patients. For comparison, the exposure rate at approximately 1 meter inferior to patient perineum was measured prior to patient release using the Inovision 451P‐RYR survey meter. Results: The distance from the edge of the prostate to skin surface along the inferior direction was the shortest in all 25 patients. The mean of the calculated exposure rates at 1 meter from skin surface was 0.53 mR/hr, 0.53 mR/hr, 0.04 mR/hr, 0.04 mR/hr and 1.5 mR/hr along the anterior, posterior, left, right and inferior directions, respectively. The mean of the measured exposure rate at 1 meter inferior to patient perineum was 1.1 mR/hr. The mean ratio of the measured versus calculated exposure rate was 0.74 (standard deviation = 0.23). Conclusions: Our calculation technique is useful in determining in advance whether a patient may require hospitalization after his implant. The exposure rate at 1 meter inferior to patient perineum is a good indicator for determining whether the exposure rate along any direction might exceed the maximum allowed patient release exposure rate of 6 mR/hr.
SU‐E‐T‐261: Determination of Initial Exposure Rates and Clearance Constants in a Sequence of 165 Consecutive Thyroid Cancer Patients Undergoing NaI‐131 Therapy
Authors: Pickering C , Dykes J , Domingo M , Yamauchi D , Patricko J , Williams L
Published: June 2012

Purpose: Following surgery, papillary and follicular thyroid cancers are usually treated with oral administration of NaI‐131. In order to estimate subsequent staff, family, and public exposures, it is important to measure both exposure rates as well as the time of clearance of residual activity from these individuals. There is the additional possibility that patient whole‐body absorbed dose estimates may be made using the data. Methods: During the historical interval 2006 – 2010, a total of 165 consecutive thyroid cancer patients were assayed at the time of activity administration and over the following several days. Using a calibrated radiation detector, exposure rates at one meter from the navel were measured between 2 and 5 times before release. By using these measurements and assuming a single‐exponential clearance, we were able to evaluate initial exposure rates as well as the biological rate constant [k(biol)] for clearance of I‐131 from the body. Results: Regression analyses were used to fit the initial exposure [X(0)] results as a function of administered activity. By least‐squares, the slope was determined to be 0.15 mR/h/mCi over a clinically determined activity range of 25 to 250 mCi. At a given activity, there was wide variation of X(0) due to individual factors such as amount of residual thyroid mass and body habitus. For example, at 150 mCi, X(0) varied from 15 to 35 mR/h at one meter with the average being 25 mR/h. For the 165 patients, the mean biological clearance constant was 0.049/h. Conclusion: Average initial exposure rates at one meter from 165 NaI‐131 patients have been determined. The biological clearance was seen to be much more rapid than the physical decay constant for I‐131 (0.0036/h). At a given activity level, variation of exposure rates was approximately +/− 40% over the corresponding patient population.
SU‐E‐T‐266: Shielding Measurements for a Proton Therapy Facility
Authors: Risolo K , Avery S , McDonough J , Bartels M , Maughan R
Published: June 2012

Purpose: This paper is a follow up on the analytical calculations for the Roberts Proton Therapy Center with empirical data to determine the precision of the calculations from Avery, et al. Methods: Neutrak dosimeters were placed in two sets around the facility while it was in operation at points of interest examined in Avery, et al. The doses to these dosimeters were recorded over one month for one set and two months for the other. Dosimeters that both recorded a dose and could be practically examined were compared to the doses predicted via the analytical method of Avery, et al. at their point of placement. Results: Two points showed a less than 10% difference to the calculated doses. One point shielded by both concrete and pre‐cast blocks and one point shielded by both concrete and the facility's cyclotron were not as precise. Conclusions: The analytical calculation method explored in Avery, et al. is fairly precise in describing the dose at various points in the facility shielded only by concrete. for materials other than concrete, such as the make‐up of the cyclotron or varying wall material, it warrants follow up calculations using the same method.
SU‐E‐T‐267: Construction and Evaluation of a Neutron Wall to Shield a 15 MV Linac in a Low‐Energy Vault
Authors: Speiser M , Hager F , Foster R , Solberg T
Published: June 2012

Purpose: To design and quantify the shielding efficacy of an inner Borated Polyethylene (BPE)wall for a 15 MV linac in a low energy vault. Methods: A Varian TrueBeam linac with a maximum photon energy of 15 MV was installed in asmaller, preexisting vault. This vault originally housed a low‐energy machine and did not havesufficient maze length recommended for neutron attenuation. Effective dose rate calculationswere performed using the Modified Kersey's Method as detailed in NCRP Report No. 151 andfound to be unacceptably high. An initial survey following the machine installation confirmedthese calculations. Rather than restrict the linac beam energy to 10 MV, BPE was investigatedas a neutron moderating addition. An inner wall and door were planned and constructed using4′×8′×1″ thick 5% BPE sheets. The resulting door and wall had 2″ of BPE; conduits and ductwork were also redesigned and shielded. A survey was conducted following construction of thewall. Results: The vault modification reduced the expected effective dose at the vault door from 36.23to 0.010 mSv/week. Conclusion: As specific guidelines for vault modification are lacking, this project quantitativelydemonstrates the potential use of BPE for vault modification. Such modifications may provide alow‐cost shielding solution to allow for the use of high energy modes in smaller treatment vaults.
SU‐E‐T‐269: The Evaluation of Copper as an Alternative for Cerrobend Electron Shielding
Authors: Chu A , Feng W , Ahmad M , Chen Z , Nath R
Published: June 2012

Purpose: To evaluate the replacement of Cerrobend by copper for electron beam cutouts. Methods: The dosimetric comparisons for circular copper‐and Cerrobend‐cutouts with diameters (1.0, 2.0, 3.0, 5.0, 7.5, 10.0, and 12.5 cm) were made using electron beams with energies (6, 9, 12, 16, and 20 MeV) from 3 Varian accelerators. A PTW Farmer chamber (0.125cc‐volume) was used for larger cutouts (diameters > 2cm), and an electron‐diode for the 2 smallest cutouts. Also a Markus parallel plate chamber was used. Results: (1) The tests showed little difference for the electron dosimetric characteristics, Eo, Eop, R50, Rp, and dmax. For larger cutout, the parameters were virtually the same for copper and Cerrobend. for smaller cutout (diameter = 3cm), small discrepancies were observed i.e. differences < 1mm for R50, Rp and dmax, =0.1MeV for Eop, and =0.3MeV for Eo. (2) The larger‐cutout outputs at dmax were also virtually the same (difference = 0.6%). For smaller cutouts (diameters = 3cm), the copper outputs were 2.0%∼5.0% higher than Cerrobend. (3) For lower energy electrons (<12MeV), more larger‐angle scattered electrons from higher‐Z Cerrobend raise the Cerrobend percentage‐depth‐dose (PDD) curve at shallow‐depths, and more forward scatter dose after dmax from lower‐Z copper shifts the copper PDD slightly away from the one of Cerrobend. for higher energy electrons (= 12MeV), the shallow‐dose difference becomes smaller for both cutouts, but even more forward‐scattered dose from copper shifts copper's PDD further away from Cerrobend's. (4) The higher X‐ray transmission through copper is also observable; i.e. 12%, 10%, and 7% for 20MeV, 16MeV, and 12MeV, respectively, but such small transmitted amount is clinically insignificant. Conclusions: Except for a higher x‐ray transmission, other dosimetric differences brought in by the replacement of Cerrobend by copper cutout are negligible.
SU‐E‐T‐278: Study of MAGIC‐F Gel and PENELOPE Code Simulation Response for Clinical Electron Beams
Authors: Pianoschi T , Alva‐Sánchez M , Santanna M , César D , Nicolucci P
Published: June 2012

Purpose: To evaluate the response of MAGIC‐f gel through dose response curves, percentage depth dose (PDD) and beam profile for clinical electron beams. Methods: Glass tubes (Vacutainer ®), with 6 cm length and 0.5 cm radius, with MAGIC‐f were positioned inside a water phantom to study the gel response with doses from 0.5 Gy to 20 Gy in electron beams of 6, 9 e 12 MeV. Glass tubes of 20 cm length and 1 cm radius and PMMA phantoms of 10 × 5 × 5 cm3 were used to PDD and beam profiles determinations, respectively, with a maximum dose of 2 Gy to the gel. The samples were analyzed through magnetic resonance imaging (MRI) with a 3 T tomography using a head coil, multiple spin echo sequence with 16 echos, TE 15ms and TR 4000ms. The MAGIC‐f response was simulated with PENELOPE Monte Carlo code in the same geometry used in the irradiations. The results obtained with MAGIC‐f and PENELOPE were compared with clinical data. Results:
Calibration curves for MAGIC‐f showed a linear behavior, with correlation coefficient of 0.99, for all energies. The PDD and beam profile curves obtained with MAGIC‐f presented differences lower than 1.5% and 3.0%, respectively, when compared to clinical data. Results obtained by PENELOPE and clinical data showed differences up to 1.0% and 1.5%, respectively, for PDD and profile curves. Conclusions: The dosimetric parameters for electron beams obtained experimentally with MAGIC‐f and with PENELOPE code showed similar results to the clinical data. From the results it can be inferred that MAGIC‐f can be used as a complementary dosimetric tool for electron beams due to its characteristics of high spatial resolution and the ability to construct tridimensional dose distributions. Also PENELOPE can be used to study MAGIC‐f gel response in electron beams.
SU‐E‐T‐283: Carbon Ion Therapy Innovations in Dosimetry and Dose Delivery
Authors: Cernica G , Mun S
Published: June 2012

Objective : Carbon ion particle therapy delivers sharp Bragg's peaks, and hence can produce dose delivery of very high precision and conformality. To complement this characteristic, particle therapy centers implement a number of technologies unique to these centers, and are not commonly known to the medical physics community. This work outlines these adopted technologies.Methods : Particle therapy centers develop technologies to meet the needs of patient safety, dose delivery accuracy, and imaging requirements complementing these state‐of‐the‐art centers. Through the use of literature reviews and publicly available documents, we produced a compilation of some of these innovations, a number of them unique to the centers themselves. Results : The centers based in Bloomington, USA, Chiba, Japan, Harima Japan, Gunma, Japan, Heidelberg, Germany, and Pavia, Italy were reviewed. Interestingly, 60% of centers reviewed developed in‐house innovations to address the needs of particle therapy, and all but one had at least one technology unique to its center. For example, Bloomington's MPRI developed a 3D dosimeter used in particle beam measurement. The patient couch systems implemented in Chiba, Japan and now Gunma, Japan are unique to the centers. Heidelberg's HIT developed the world's first carbon ion gantry. Italy's CNAO has a unique patient positioning system.Conclusions : Particle therapy centers, despite being at the forefront of technology in delivering radiation to patients, have not widely disclosed treatment delivery strategies and dosimetry techniques, despite the material being potentially useful to the radiotherapy community. This work is an effort in comparing and contrasting these innovations.