bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐15: Parameterization of the Photon Beam Dosimetry
Authors: Lebron S , Li J , Yan G , Kahler D , Liu C
Published: July 2013

Purpose: In radiation therapy, obtaining accurate data for photon beam dosimetric quantities such as fractionated depth doses (FDDs), profiles and output factors (OFs) is important since it affects the accuracy of dose calculation for patient treatment. The purpose of this study is to develop methods to parameterize all photon dosimetry parameters for a specific linear accelerator model and to create an expert data set in order to (1) minimize the interpersonal measurement uncertainties, (2) automate the quality assurance program, (3) minimize data collection during machine commissioning and (4) implement analytical de‐convolution method to remove the detector volume averaging effect. Methods: OFs, FDDs and profiles for different field sizes and depths were measured in an Elekta linear accelerator using a cylindrical 3D scanner (SunNuclear). All data were smoothed for the analysis and profile data were also centered and symmetrized. The OFs were analyzed using a polynomial equation. The FDDs were analyzed using two Methods: one consisted of a ratio of two exponential functions to parameterize the whole curve and the other dividing the curve into two parts characterized by Gaussian and polynomial functions. For profile modeling, half side of the profile was divided into four regions described by four different Gaussian equations. This set of equations was used to model the photon beam dosimetry for various field sizes and depths. Results: The differences between measured and modeled data were less than: 0.002% for OFs, 0.1% and 3.4% for FDDs for the first and second method respectively and 0.1% for the profiles. The calculated data generated an R2 =1 for the OFs, R2 >0.993 for the FDDs, and R2 >0.99 for the profiles. Conclusion: This novel analytically calculated model proved to be accurate in calculating the FDDs, profiles and OFs for different field sizes and depths.
SU‐E‐T‐18: GATE Monte Carlo Simulation in a Cloud Computing Environment
Authors: Rowedder B , Kuang Y
Published: July 2013

Purpose: The GEANT4‐based GATE is a unique and powerful Monte Carlo (MC) platform, which provides a single code library allowing the simulation of several specific applications, e.g. PET, SPECT, CT, internal and external radiotherapy, and hadron therapy. However, its lengthy computing time hinders its routine use in the clinic. Reducing its computing time is therefore of great importance. Thus, a commercial cloud compute service is well suited for GATE MC simulation, both in terms of cost and efficiency. This study achieves a reliable and efficient execution of GATE MC simulation and provides execution frameworks to end‐users. Methods: The GATE software was ported on a commercial compute cloud environment — Amazon Elastic Compute Cloud (EC2). Simulation data was initially loaded onto the master node, and then distributed among independent worker nodes. The filed output from EC2 was sent down to the Amazon Simple Storage Service (S3). The results were finally aggregated on the local computer for display and data analysis. The distributed implementation was executed using a photon beam interacting in a 40 cm by 40 cm by 40 cm water phantom and a four‐head SPECT imaging as benchmarks. Results: A cloud computing environment led to increased calculation speed for the cases implemented in this study. The speed increase scaled approximately linearly with the number of nodes used for computing. The output of the cloud‐based GATE MC simulation was identical to that produced by the single‐threaded implementation, and was resilient to hardware failure, indicating the reliability of the cloud computing platform. The user‐friendliness offered by the workflow implementation does not introduce significant overhead. Conclusion: A cloud computing infrastructure has been established for GATE MC simulation. It substantially improves the speed of simulation, and makes rapid MC simulation for imaging/radiotherapy application possible.
SU‐E‐T‐29: Monte Carlo Calculated Output Corrections Factors K(Q,f‐Clin) for Varian_Clinac‐IX 6MV Small Fields
Authors: Benmakhlouf H , Sempau J , Andreo P
Published: July 2013

Purpose: To determine detector reading corrections for small fields from a Varian_Clinac‐iX 6 MV linac, according to the international IAEA‐AAPM formalism (Alfonso et al 2008) for different detectors. Methods: The correction factor k(Q,f‐clin) was calculated as the ratio of two MC calculated absorbed dose ratios, water to detector, for small clinical fields relative to the standard reference field of 10cmx10cm (machine‐specific‐reference field). Absorbed doses to various detectors positioned at 10 cm depth in water were calculated using the MC system PENELOPE/penEasy. Phase‐space files for field sizes between 0.5 cm and 10 cm from the IAEA phase‐space database were used as radiation sources to simulate the response of the detectors PTW T60017 (unshielded diode), PTW T60016 (shielded diode), PTW T31018 (liquid ion chamber, LIC) and IBA SFD (unshielded diode). Results: For the two unshielded diodes, the corrections are up to 2% at intermediate fields (>1 cm side), becoming down to −5% for fields smaller than 1 cm. The shielded diode corrections decrease with field size from 0 to −9%. The correction for the LIC is within +−1% for all fields. Conclusion: Shielded diode corrections are smaller than one due to the unbalanced lateral charged particle equilibrium between silicon and water. To this effect, unshielded diode corrections add the well‐known gradual over‐response to low‐energy scattered photons in large fields (maximum for 10cmx10cm). All diode corrections are shown to be significant for field sizes smaller than 2 cm, being appreciable (up to 2%) at intermediate fields for the unshielded diodes. Normalization at fields smaller than 10cmx10cm partially masks the over‐response of unshielded diodes. Results are consistent within 0.5% with other (EGS‐based) MC calculations, some made for different 6 MV linacs (Siemens, Elekta). Differences can be used to estimate a type‐B uncertainty. Financial support from Radiation Safety Authority (SSM) (SSM2012–2331) is acknowledged.
SU‐E‐T‐32: Monte Carlo Determination of WAFAC Corrections for the Canadian LDR Primary Standard
Authors: Mainegra E , Shen H , McCaffrey J
Published: July 2013

Purpose: Determine correction factors for a wide angle free‐air chamber (WAFAC) using Monte Carlo techniques for the realization of the air‐kerma strength, Sk, for low dose rate (LDR) 125 I and 103Pd brachytherapy sources. This WAFAC will become the Canadian primary standard for LDR brachytherapy sources. Methods: The EGSnrc user‐code egsfac is used for estimating the correction factors required to determine the air‐kerma at the WAFACs point of measurement (POM) using MC simulation for a 125 I and a 103Pd source. The geometry library egs++ allows simulation of the sources and the WAFAC in detail. Spectra are taken from the most recently published data. Air and aluminum attenuation curves for the 125 I seed were also measured with the WAFAC. Results: Correction values compared with those reported by NIST for its LDR primary standard (of very similar design) are in excellent agreement when using the NIST approach of assuming an isotropic point source and using experimental main spectrum lines. Differences in both methodologies for determining the WAFAC corrections are discussed and their impact evaluated. The effect of the source and the holder on the scatter correction is quantified separately. The calculations resulted in a modification of the design to reduce collimator transmission. A 3.2 mm lead sheet was added behind the WAFAC aperture, attenuating the 1251 and the 103Pd photon beams to less than 0.02 %. MC attenuation curves for air and aluminum for the 125 I seed are in good agreement with experimental data. The largest correction is the aluminum filter attenuation which can be as large as 4 %. Conclusion: Despite an inconsistency in the scatter estimation, the NIST approximation has little impact on the determination of Sk. The scatter correction is sensitive to the collimation system dimensions. Using MC‐based air and aluminum attenuation corrections for the 125 I seed is experimentally justified.
SU‐E‐T‐39: A Study of Dose Response Characteristic for Gafchromic EBT2 Film
Authors: Chen W , Di X , Wang S , Wang B , Bai X , Yang J , Guo B , Huang K
Published: July 2013

Purpose: The self‐developing Gafchromic EBT2 film (International Specialty Products, Wayne, NJ) is a radiochromic film widely used for relative photon dosimetry. Different from the traditional radiochromic film, EBT2 is colored, hence the dose response sensitivity of EBT2 film will be different when the film is scanned by different light source. The dosimetry software FILMQA provides the function to separate 48 bits color image into three 16 bits gray maps corresponding red, green and blue scanner light respectively. We focused on studying the dose response characteristic of EBT2 film when it was scanned by red, green and blue light source. Methods: The EBT2 film was placed in solid water phantom, radiated with 6MV photon beam. Delivered dose to the film spanned from 0 to 280 cGy. The film was scanned with flatbed color scanner and the scanned images were separated into red, green and blue channels respectively. The characteristic of image's dose response was analyzed. Results: The dose response sensitivity of the EBT2 film is different when it was scanned by different light source. The sequence of dose response sensitivity is 109.8, 88.1 and 29.9 (Apixel value/AcGy)corresponding to scanner light source in red, green and blue. Cubic polynomial fitting method can satisfy the requirement of dose response curve. Conclusion: Dose response sensitivity of EBT2 films descended with the increased of absorption dose. The dose response ability appears different when it is scanned in different light source.
SU‐E‐T‐160: Exit EPID Image Prediction Below Heterogeneous Phantoms Using Monte Carlo Codes
Authors: Yoon J , Kim J , Jung J , Yeo I
Published: July 2013

Purpose: To predict accurate exit EPID images below lung or bone phantoms by appropriate Monte Carlo modeling. It has been evaluated that XVMC and EGSnrc Monte Carlo codes are suitable for dose calculation in tissue equivalent material at both patient and EPID levels. However, the EPID image prediction is challenging due to its complex structure and material composition of high atomic number. Methods: A 6MV beam and phantom were modeled using BEAMnrc and XVMC codes. The accuracy of exit dose was validated through comparison with 2‐D ion chamber dose under a 2 cm build‐up layer. After the validation, Varian aS1000 EPID has been modeled to calculate the EPID response. The material composition of EPID has been used for modeling in EGSnrc user code, DOSRZnrc, whereas homogeneous layer modeling by density scaling of the composition has been applied in XVMC. Dose images at 150 cm were calculated under combinations of plastic water, lung and bone flat phantoms for various field sizes. The results were compared to EPID measurement. Results: Ion chamber array measurements at EPID level agreed with the XVMC and BEAMnrc/DOSRZnrc calculations within ∼3%. EPID images calculated by DOSRZnrc were in good agreement (∼1%) with the measurement in all cases. The results from XVMC were within ∼2% difference in plateau region, but penumbra slopes were sluggish and dose response at off‐axis was slightly lower. Conclusion: EPID dose images were calculated through EPID composition modeling by XVMC and BEAMnrc/DOSRZnrc. Both Monte Carlo calculations agreed with the measurements in all settings, except penumbra slopes and off‐axis responses in XVMC calculations. The EPID model by XVMC can be used for faster and less accurate calculations, whereas the other for more accurate, time spending calculations.
SU‐E‐T‐175: ArcCheck Hypothesis Testing: Is Dose Error in a Phantom Applicable to the Patient?
Authors: Barbiere J , Ndlovu A
Published: July 2013

Purpose: The purpose of this work is to present a technique by which we are able to measure the error produced by computing the delivered dose to a patient based on the dose delivered to a uniform density cylindrical phantom. Methods: ArcCHECK by Sun Nuclear (3DVH, Sun Nuclear Corp., Melbourne, FL) has the desirable ability to perform VMAT QA and configure the results in the form of a DVH similar to the original plan evaluation. In this work we examine the hypothesis that measured errors in a phantom translate very closely to those in a 3D patient. It is possible to create Verification Plans (VP) whereby the treatment fields for a lung patient are applied to both the patient data set (VPpatient) and a predefined phantom data set (VPphantom). The VP 360 arcs are subdivided into 30 degree sectors. The most useful feature of the VP is that we now have the ability to make changes. Each of the individual sectors is essentially an independent control point with alterable treatment aperture and Monitor Units. We modified a control point in the phantom (VPphantomModified) to see the effect on the patient (VPpatientModified). We tested the hypothesis in the two dimensional isocenter plane by exporting the four relevant dose matrices to MATLAB and performing the calculations as described by Sun Nuclear. Results: The amount of error greater then the traditional acceptance vale of 3% can be significant. Most of this error is concentrated in the lung and rib regions as would be expected from their greatest deviation from the uniform density in the phantom. Conclusion: This work shows a technique whereby the user of Sun Nuclear ArcCHECK can verify and quantify the hypothesis that measured dose error in a homogenous phantom is applicable to a heterogeneous patient.
SU‐E‐T‐197: Is the COMPASS 3D Dosimetry System An Accurate and Safe Quality Assurance Tool for Verifying Stereotactic Body Radiotherapy Dose Delivery for Non‐Small‐Cell Lung Carcinoma?
Authors: Hu B , Huq M
Published: July 2013

Purpose: Quality assurance for small field fractionated stereotactic radiotherapy treatment is critical and challenging due to the resolution of detectors used for measurements. We evaluate whether COMPASS system can be used as a good QA tool for SBRT dose delivery. Methods: 40 SBRT NSCLC cases were utilized in this study. PTV size ranged from 3cmx3.4cm to 8.1cmx6.7cm. Prescription doses to PTVs were 30Gy to 60Gy delivered in 3 to 5 fractions. For each case, a representative plan designed in Eclipse AAA using either RapidArc or dynamic‐IMRT was sent to COMPASS for calculating predicted dose. The reconstructed dose distributions were updated by using the measurement corrections. Measurements were made using a MatriXX Evaluation system mounted on the gantry at a SDD of 76.2cm, with a resolution of 7.62mm. The target dose‐volume parameters of D99%(dose received by 99% of target volume), D95%, D85%, D80%, D50%, D30%, D20%, D10%, D1%, average dose, and average gamma were analyzed against that of Eclipse. The OAR dose differences of the average dose and average gamma were also compared. Results: Compared to Eclipse, PTV average dose in COMPASS varied by 0.8% from predicated dose, and by 1.9% from reconstructed dose. PTV dose‐volume parameters show good agreement on predicated dose(±3%) and relatively poorer agreement on reconstructed dose(±7%). PTV dose‐volume parameters in low dose region show a better agreement than that in high dose region. The average gamma differences were up to 0.6 in PTV and 0.15 in OARs. The average absolute dose difference shows a maximum of 0.17Gy in OARs. There is no significant difference between VMAT and IMRT plans. Conclusion: COMPASS can be used as an independent QA tool for small field SBRT. COMPASS predicated doses show a better agreement with Eclipse when compared to reconstructed dose distributions. The limitation of the MatriXX resolution should be considered.
SU‐E‐T‐215: The Effect of Treatment Plan Complexity On Optically‐Stimulated Luminescent Dosimetry
Authors: Kuruvilla A , Rea A , Riegel A , Kapur A , Jamshidi A , Potters L
Published: July 2013

Purpose: The purpose of this study was to characterize uncertainties in radiation dose to optically‐stimulated luminescent dosimeters (OSLDs) for varying levels of field modulation. Methods: We considered 7 conformal treatment plans (25 fields), 9 enhanced dynamic wedge plans (21 fields), and 4 IMRT plans (28 fields). Five OSLDs arranged in a plus shape on 9 cm of solid water buildup were covered with 5 mm bolus and scanned using a large bore CT scanner. The images were imported into the treatment planning system. Each field of each plan was projected onto the phantom surface at gantry angle 0°, the field isocenter was placed at 10 cm depth, and dose was calculated using collapsed cone convolution and a 4 mm dose grid. The expected point dose to each OSLD was measured in the phantom plan. The OSLD geometry was replicated on a linear accelerator, and all 3D conformal, wedged, and IMRT fields were shot using 6 MV photons. All exposed OSLDs for each field were read approximately 18 hours later and measured doses were compared with planned doses. Results: For open, wedged, and IMRT fields, measured doses were 2.3% ± 4.1% higher, 0.9% ± 6.1% higher, and 2.6% ± 14.0% higher than planned doses respectively. The standard deviation was greatest for IMRT plans and lowest for 3D conformal plans. A few IMRT fields demonstrated substantial differences between planned and measured doses for individual OSLDs (over 60%). After further analysis, these large discrepancies occurred when leaf edges fell on or near the dosimeter position. Conclusion: Uncertainties in dose were much higher with IMRT fields than 3D and wedged fields. Increasing modulation increases dose uncertainty. Further research will investigate the effect of dose grid resolution and calculation model, specifically the advantages of Monte Carlo calculations near the skin surface.
SU‐E‐T‐235: A Comparison of Small Field Output Factors for Three SRS/SRBT Systems
Authors: Gao W
Published: July 2013

Purpose: Dosimetry measurement for small fields used in SRS/SBRT is challenging and the results can vary between institutions especially when different detectors are used. There are several reports in recent years that serious errors occurred in SRS/SRBT treatments due to incorrect output measurements in the initial commissioning processes. The present study compares small field output factors measured using a same detector for 6 MV photon beams in three SRS/SRBT systems: Cyberknife (cone), Brainlab (cone), and Varian TrueBEAM (Jaw), and determines if they are close enough to be used for reference purposes in commissioning similar SRS/SRBT systems. Methods: Relative output factors of small fields were measured by the author using a SRS diode (PTW 60012) in water for 6 MV photons with Cyberknife cones (5 to 60 mm), Brainlab cones on Varian TrueBEAM (5 to 30 mm), and TrueBEAM (Jaw: 10 × 10 mm2 to 40 × 40 mm2). The results are compared after being corrected for differences in reference field sizes, measurement distances and depths as defined in the three computer planning systems. Results: The corrected relative output factors of small fields measured for three systems are within +−2% from the average for collimator sizes larger than or equal to 20 mm, and within +−3% for smaller fields. Conclusion: The Results suggests that it may be feasible to establish a reference dataset of small field output factors for various SRS/SRBT systems and beam shaping devices (cone and MLC), similar to the RPC standard dataset for IMRT fields. Such a reference dataset is not to replace data collections during the institutional commissioning processes, but rather, is used as a secandary check to alert possible errors when large deviations from the reference data are observed.
SU‐E‐T‐239: Implementation of QA Procedures and Their Effect On the Radiation Treatment Delivery Error Rate Over a 12 Year Period
Authors: Wasserman S , Feygelman V , Moros E
Published: July 2013

Purpose: Treatment deviations have been tracked from 2000 to the present covering over 23,000 treatment courses and 420,000 fractions. During this period multiple error reduction actions were taken including implementation of an electronic record and verify system (ERVS), a departmental weekly QA meeting, a time out procedure, a dosimetry boarding pass and ACR accreditation preparation. This study will examine error rates before and after these actions to estimate the effect on the overall and categorical error rates. Methods: A treatment deviation was defined as any error in radiation treatment delivery that reached the patient. Deviations were catalogued by type of error, detection method, number of fractions delivered prior to detection, and percentage of treatment course affected by the deviation. Results: The use of ERVS was incrementally applied to linacs from 1999 until 2006 by which time all linac treatments were electronically verified. In 2006 a weekly QA meeting and a requirement for a patient specific dosimetry boarding pass were started. A treatment timeout procedure was initiated in 2007. Standards were modified to meet ACR standards during 2007–08 resulting in accreditation. From 2000– 2002 the overall error rate averaged 5.4 per 1000 treatments (0.0054) and decreased to 0.0024 for the 2005–2007 period with 2004 being an outlier due to a single upstream error affecting multiple patients. The rate continued to decline to 0.0019 for 2008– 09 and to 0.0010 for 2010–12. Conclusion: Simultaneous technology and procedural changes make it difficult to correlate the effect of individual changes directly to the error rate. Nevertheless, the data clearly shows a progressive error rate reduction as QA procedures were implemented. Reduction in some classes of errors can more easily be tied to specific changes. We believe the combined implementation strongly contributed to an overall culture of safety resulting in a reduced error rate.
SU‐E‐T‐244: Interfractional Motion Simulation of Head and Neck and Lung Patients Correlated to Treatment Outcome
Authors: Zuniga A , Apte A , Bradley J , Thorstad W , Deasy J
Published: July 2013

Purpose: To quantify the correlation between gross tumor volume (GTV) margins and local control (LC) outcome in head and neck (H&N) and non‐small cell lung cancer (NSCLC) patients. Methods: Interfractional motion simulation was done using the robustness analysis tool in CERR. This tool applies shifts to individual patients fraction by fraction within an entire course of treatment obtaining a final integral dose distribution. The shifts are defined assuming a Gaussian distribution of possible positioning for every fraction. Because of their fractionation schemes, 35 shifts were applied to the H&N, and 30 to the NSCLC dataset. We applied isotropic random shifts sampled from three independent normal distributions all with standard deviations of 3mm. Systematic errors were not included in this study, nor roll rotations. We repeated the process 10 times and averaged the integral doses. Ring structures around the GTV extending isotropically were created. The ring's width ranged from 2 mm to 15mm in H&N, and from 2mm to 20mm in NSCLC. A cell‐kill based equivalent uniform dose (cEUD) metric was calculated for each structure. A logistic regression model was built using cEUD for the margins and for the GTV. LC prediction was evaluated using Spearman correlation coefficient (Rs) on the entire datasets and also on cross‐validation. Results: Adding a margin to GTV did not improve LC correlation in H&N after cross‐validation (Rs= 0.398 p=0.0003 for the GTV alone, and Rs= 0.371 p=0.0007 for the next best added margin). For NSCLC we improved from Rs=0.393 (p=0.003) to Rs=0.413 (p=0.0015) at 5mm margin. Conclusion: Our analysis suggests that in H&N the dose given to the tissue surrounding the GTV is not correlated with LC, but it is for NSCLC. This may be because immobilization devices and setup verification systems are more accurate in H&N and also because the differences in prescription doses.
SU‐E‐T‐249: Information Systems Infrastructure and Architecture for a Large Integrated and Centralized Oncology System
Authors: Izadbakhsh M , Le A , Brandner E , Heron D , Huq M
Published: July 2013

Purpose: To design and implement an Oncology Information System (OIS) around an existing IT infrastructure to optimize performance, meet clinical requirements, and minimize implementation costs. University of Pittsburgh Medical Center (UPMC) is a large health system with 50 medical and radiation oncology centers. To improve the quality, safety, and efficiency of patient centric care, an initiative was undertaken to integrate the patients' data and health information of all cancer centers on a centralized OIS with interfaces to the rest of the UPMC and affiliated hospitals. Methods: The OIS must incorporate the existing isolated oncology systems and devices and aggregate all of the patient's electronic medical records (EMR) including imaging, planning, and treatment creating a single point of patient information reference built upon the existing UPMC infrastructure. The distributed nature of UPMC CancerCenter and its multi‐vendor systems requires rigorous evaluation and testing for multiple levels of software, hardware, infrastructure, and environmental platforms and comparison and validation of their capabilities with the clinical workflow. Results: We successfully implemented the “integrated and centralized” OIS with ARIA at 16 of the 22 radiation and 5 of the 28 medical oncology sites at the rate of 1 site every 2 months. We completed all inbound and outbound interfaces transferring data to and from ARIA and other UPMC systems. We interfaced 1 of 9 affiliated Non‐UPMC health systems. Conclusion: To fit the OIS technical and clinical requirements with existing health system IT infrastructure and maximize the OIS performance at minimum cost, we customized OIS data locations providing the best data flow patterns across the network. This provided a comprehensive Electronic Health Record from multiple EMRs and platforms giving physicians a unique view into each patient's information. The OIS optimized the best options for medical oncology, radiation oncology, image based planning, and image guided radiotherapy and radiosurgery.
SU‐E‐T‐252: Micro‐Sized Implantable Electrocardiogram (ECG) Sensor for Real‐Time Monitoring of A trial Fibrillation
Authors: Lee J , Park H , Son C , Kim Y
Published: July 2013

Purpose: In this study, we present an implantable ECG sensor to monitor atrial fibrillation patients in real time. Methods: The developed implantable sensor is composed of a micro controller unit, analog to digital converter, signal transmitter, antenna, and two electrodes. The sensor detects ECG signals from the two electrodes and transmits these signals to the external receiver that is carried by the patient. The sensor continuously transmits signals, so its battery consumption rate is extremely high. To overcome this problem, we consider using a wireless power transmission module in the sensor module. This module helps the sensor charge power wirelessly without holding the battery in the body. The size of the integrated sensor is approximately 0.12 inch x 1.18 inch x 0.19 inch. This sensor size is appropriate enough for cardiologists to insert the sensor into patients without the need for a major surgery. The data sampling rate was 300 samples/sec, and the frequency was 430 Hz for signal and power transmission. Results: The proposed sensor was validated with shielding experiments to mimic the action of the implant and the shielding of sensor effects. The cylindrical case for the experiment was made of three different materials: quartz, titanium, and acryl. The sensor, which transmits signals to the external receiver, was placed into the cylindrical case. The experiments showed that the sensor transmits ECG signals correctly with the three different types of case materials. The quartz material shows the best results among the three materials because it sends data without any distortion. Conclusion: An implantable ECG sensor that is composed of a wireless signal transmitter, wireless power receiver, and two electrodes was designed and experimentally evaluated. The work presented in this study is an initial step toward the real‐time monitoring of atrial fibrillation patients. This work was supported by a Grant (No. 10041876) from the Technology Innovation Program funded by the Ministry of Knowledge Economy(MKE, Korea).
SU‐E‐T‐261: Dosimetric Characterization and Comparison of the Elekta Agility and MLCi2 Multi‐Leaf Collimator Heads
Authors: Cutright D , Gopalakrishnan M , Sathiaseelan V , Lurie Robert H
Published: July 2013

Purpose: The new Elekta Agility™ radiation head with integrated 160 × 5mm inter‐digitating tungsten‐alloy leaves has been designed with leaf sides tilted to reduce overall transmission and leaf leakage. In this study, a comparison of the major dosimetric parameters of the Elekta Agility™ 160 leaf (5mm leaf width) multi‐leaf collimator (MLC) head design and the older Elekta MLCi2™ 80 leaf MLC head (10mm leaf width) is presented. Methods: Electron and photon beam data (including PDDs and profiles for various field sizes) were collected and analyzed using IBA hardware and software products for linac commissioning (i.e., IBA water tank, diodes, and OmniPro Accept™ 7). MLC transmission and leakage was measured using gafchromic film and SunNuclear MAPcheck2™. Results: Photon beams: Percent depth doses for 6MV and 10MV photon beams with various field sizes indicated little difference between the MLCi2™ and Agility™ heads (i.e., less than 1% difference at depths beyond dmax). Penumbra and umbra of dose profiles matched well for both energies; marginally differences were noticed on the toe‐side of large wedged‐fields. The average Agility™ MLC transmission was measured to be 0.4%, nearly an order of magnitude lower than the MLCi2™. Collimator scatter factors were nearly identical for small fields and reduced by as much as 1% for larger fields.Electron beams: PDDs of electron beam energies of 6, 9, 12, 15, and 18 MeV were collected, indicating little differences between the Elekta Infinity™ with the MLCi2™ and Agility™ heads. Conclusion: Analysis of the MLCi2™ and Agility™ beam data indicate little to no undesirable dosimetric differences; the largest deviation being a significant decrease in MLC transmission and leakage. These characteristics, combined with a significant increase in leaf speed, make the Elekta Agility™ a considerable improvement over the MLCi2™.
SU‐E‐T‐264: CTRC Experience: Patient Specific IMRT Quality Assurance with Ionization Chamber and Detector Arrays
Authors: Cruz W , Stathakis S , Mavroidis P , Esquivel C , Papanikolaou N
Published: July 2013

Purpose: This study was conducted to review the IMRT QA results of patient plans (grouped by anatomical site, MLC type, and TPS) delivered at the Cancer Therapy and Research Center using Varian LINACs and Hi Art Tomotherapy units. Methods: The patient data was evaluated for the time period 2006–2011 and it involved several methods used in the QA process. Ion chambers and film were used in the earlier years followed by ion chamber arrays in the latter years. The patients were grouped according to several parameters including site of treatment, type of machine, and magnitude of the differences between measured and planned data. From 2006 until 2009, 736 tomotherapy plans, 817 Pinnacle3 plans, and 351 Corvus plans were evaluated using ion chambers and film. The pass criterion at the institution at the time of these measurements was 3% dose difference and 3mm distance agreement. For the period 2009–2011, 1466 patient IMRT QAs were performed on Varian linacs, which were equipped with Millennium 80, 120 and High‐Definition 120 multileaf collimators and they were evaluated according to pass criteria of the institution (gamma = 90%). Results: The average gamma values of the brain, head and neck, thorax, abdomen, and pelvis cancer cases were 97.2%, 95.7%, 96.2%, 97.0%, and 96.2%, respectively. The average gamma values based on the 80, 120, HD 120 and Tomo MLC configurations were 96.5%, 96.2%, 96.3%, and 97.0%, respectively. The average differences between the measured and calculated plans for the Pinnacle3, Hi‐ART TomoTherapy, and Corvus treatment planning systems were 2.3%, 0.004%, and 0.02%, respectively. Conclusion: Based on the anatomical site, head and neck cancers had the lowest gamma value for the patients treated and the brain cancers had the highest gamma value. The TomoTherapy machines had the best overall gamma values as compared to the CLINAC machines.
SU‐E‐T‐265: Measurement of Secondary Neutrons Produced in the (gamma,n) Reaction From the TrueBeam Linac Head
Authors: Harvey M , Pollard J , Wen Z , Gao S
Published: July 2013

Purpose: The purpose of this study was to measure secondary neutrons produced via the (γ,n) reaction in the linac head of the Varian TrueBeam system for 10 MV and 15 MV x‐ray beams, respectively. Of note is that there is currently no measured data available in the literature on secondary neutron production from the TrueBeam treatment head. Methods: The linac was operated in flattening filter‐free (FFF) mode for the 10 MV beam and flattening filter (FF) mode for the 15 MV beam with the jaws and multileaf collimators in the fully closed position. A nominal setting of monitor units per minute (MU/min) were delivered for each beam energy and the secondary neutron dose rate was measured in triplicate using a LudLum neutron survey meter (model 12‐4) positioned at multiple locations including isocenter, longitudinal (gun‐target) and lateral to the isocenter. Results: For the 15 MV x‐ray beam (FF), 600, 300 and 100 MU/min were delivered. The secondary neutron dose rate peaked at a distance of 20 cm longitudinal to the isocenter at 600 MU/min and decreased with distance from the isocenter. Fluctuations in the longitudinal neutron dose rate were negligible; however, the lateral neutron dose rate varied up to nearly a factor of 2 away from the isocenter with decreasing MU/min. For the 10 MV x‐ray beam (FFF), 2400, 1200 and 400 MU/min were delivered and the secondary neutron dose rate was again observed to peak around 20 cm longitudinal to the isocenter with fluctuations varying by about 50% with decreasing MU/min in positions lateral to the isocenter. Conclusion: Our preliminary results suggest a secondary neutron dose rate on the order of a 45 mSv/hr or less for all measurements considered in this study indicating a relatively low contribution of produced secondary neutrons to the primary therapeutic beam.
SU‐E‐T‐274: Dosimetric Indicators of Radiation‐Induced Toxicity in Meningioma Patients
Authors: Yin L , Kremmel E , Alonso‐Basanta M , Munbodh R
Published: July 2013

Purpose: In this study, we retrospectively reviewed treatment plans and normal tissue toxicities for patients who were treated for meningiomas to investigate the correlation between DVH parameters and late Grade 3 radiation‐induced brainstem toxicity and hearing or vision changes. Methods: We analyzed data from 26 patients treated for brain meningiomas with either proton radiation or photon IMRT (11 were treated to 54Gy and 15 to 59.4Gy or higher) between 2009 and 2012 at the University of Pennsylvania. Five patients developed late Grade 3 toxicity with the remaining patients having late Grade 2 toxicity or less. Eight patients experienced hearing changes and seventeen experienced vision changes. We evaluated the maximum brainstem dose and volume of brainstem receiving more than 50∼54Gy for late Grade 3 toxicities. We also evaluated maximum and mean doses to the optic structures and cochlea. Statistical significance of the correlation between late Grade 3 toxicity or hearing and vision changes and the above mentioned DVH constraints was evaluated using Fisher exact test (two‐tailed). Results: The proportion of patients with Dmax > 45Gy or Dmean > 30 Gy for the cochlea was significantly greater in patients with hearing changes (p < 0.05 and p < 0.1 respectively). While for the brainstem a difference in the proportion of patients with and without late Grade 3 toxicity and with V54Gy > 5% was observed, this difference did not reach statistical significance. Conclusion: Differences were observed in the DVHs of meningioma patients who experienced radiation injury after radiation therapy. The mean dose to the cochlea is related to the likelihood of developing hearing changes. Based on the results of this study, dose volume parameters (that is, V54Gy) for the brainstem may be expected to be associated with Grade 3 toxicity in a larger cohort of patients.
SU‐E‐T‐275: Voxelized Second Cancer Risk Calculation — Comparison of Proton and Photon Radiotherapies for Hodgkin Lymphoma
Authors: Homann K , Newhauser W , Howell R , Eley J
Published: July 2013

Purpose: The purpose of this study was to compare the risk of developing a second lung or breast cancer for a female Hodgkin Lymphoma patient treated with passively scattered proton therapy (PSPT) and photon intensity modulated radiotherapy (IMRT). Particular objectives of this work were to fully account for stray dose, perform voxel by voxel risk calculations, and to visually display risk in a manner analogous to dose visualization used in commercial treatment planning systems (CTPS). Methods: Clinically approved PSPT and IMRT treatment plans were designed using a CTPS and prescribed 36 Gy to the target volume. Neutron and stray photon dose were calculated using an in house Monte Carlo code and a TLD measurement fitted analytical model for PSPT and IMRT, respectively. For lung and breast, therapeutic and stray doses were summed and input into an in‐house program that calculates Excess Absolute Risk (EAR) per voxel in the patient based on the RadRAT risk model. The radiation weighting factor (Wr) varied for neutron doses (Wr =10 and 30) to account for biological uncertainties. Results: Neutron equivalent doses added an additional 3% (Wr =10)/9% (Wr =30) of the prescribed dose to the CTV and near field organs. Scatter dose added an additional 5% (Wr =10 )/15% (Wr =30) of the prescribed dose to organ portions far out of field. PSPT registered a lower EAR compared to IMRT except for lung when Wr =30. Larger differences were seen in low dose regions of organs. Conclusion: EAR was lower for PSPT versus IMRT unless neutron Wr values were very high, e.g.> ∼20. More work incorporating uncertainties must be done before definitive answers are determined. In the future, similar types of risk visualization tools could be incorporated into treatment plan analysis to prospectively select plans with the lowest predicted risk of second cancers. This research was supported in part, by the National Cancer Institute award 1R01CA131463‐01A1 (W.D. Newhauser, P.I.) and a subcontract of that award (R.M. Howell, P.I). No conflicts of interest to disclose.
SU‐E‐T‐341: Experimental Evaluation of Free Radical Generation in Nanoparticle‐Aided Radiation Therapy
Authors: Paudel N , Shvydka D , Findsen E , Parsai E
Published: July 2013

Purpose: Use of gold nanoparticles (NPs) in radiation therapy has been found promising due to the possibility of selective radiation dose enhancement within a tumor, and favorable biological compatibility. Recent studies demonstrated that the biological effect exceeds the expectations based on the physical energy deposition solely, thus pointing toward biochemical factors. Since free radicals are responsible for the majority of the biological damage, evaluation of their radiation induced free radicals near the gold‐tissue interface offers a more relevant estimate of the biological damage in NP‐aided radiation treatments. Methods: Samples in the capillaries were irradiated with clinical Ir‐192 HDR source. Since free radicals are very short‐lived (∼nanoseconds), we used a spin trap agent, high purity DMPO dissolved in water, to trap hydroxyl radicals generated by radiolysis of water. The formed spin adducts retain spin properties of free radicals for a prolonged time (∼hours), especially at low temperatures. Radicals were detected via electron spin resonance (ESR) spectrometry technique. Quantification of free radicals generated in water and in the presence of a thin gold wire was done by double integration of the obtained spectra. Results: Our Monte Carlo simulations demonstrated that the dose enhancement region is limited to a close vicinity (less than 1mm) of the gold‐tissue interface still suitable for free radical measurement with ESR spectroscopy. We have established a protocol for quantitative ESR measurements. The radical generation was found to be proportional to the radiation dose, and strongly enhanced by the presence of gold. Conclusions: Free radicals generated by radiolysis of water can be measured quantitatively with ESR technique. Our evaluation of radiation induced free radical generation in water with nanoparticles sheds some light on the effects of NPs in biological systems. This project is supported through an NRC grant for faculty development. It is grant number NRC‐HQ‐12‐G‐38‐0042.
SU‐E‐T‐345: Dose Comparison of TG‐43 and Acuros Algorithm to Account Lateral Scatter in Dose Distribution
Authors: Deshpande S , Patwe P , Avdhoot S , Anand V , Bajpai R , Kannan V
Published: July 2013

Purpose: To study Effect of lateral scatter in dose distribution in Ir192 HDRBTMethods: Brachytherapy phantom was fabricated using tissue‐equivalent material E.D.1.045gm/cm3 Phantom has provision to place plastic catheters at every 5mm and TLD and Gafchromic film at every 10 mm distance along vertical direction.Phantom CT scan was performed, images were transferred to Brachyvision TPS, which has option of analytical dose calculation algorithm Acuros.Acuros is Grid Based Boltzmann Solver code which solves Linear Boltzmann equation. We reconstructed single catheter at 5 mm from edge of phantom with three source dwell positions, 10mm apart. Dose was prescribed to single point at 10 mm from central source along transverse axis.Dose calculation was done using TG43 and Acuros algorithm. Dose was measured at 10, 20and 30 mm depth using TLDs and GafchromicEBT3 films. Same procedure was repeated by placing catheter at 10mm, 15mm, 20mm and 30mm from the edge of phantom. Results: For prescription point 5mm away from edge of phantom, where scatter contribution to total dose is minimum, we found TG43 overestimates dose by 4.5% compared to Acuros. As we move away from edge of phantom lateral scatter contribution increases, dose calculation variation between two algorithms decreases and is within 1% at 20mm from edge of phantom.At greater depths, catheter close to phantom edge we observed TG43 overestimates dose by 7% at 20mm and 10 % at 30mm depth. For catheter at 20mm from phantom edge, TG43 overestimates dose by 3% at 20mm and 4 % at 30mm depth. These results were confirmed by measurements of TLD and Gafchromic filmsConclusion: Non consideration of lateral scatter contribution by TG43 can leads to dose variation up to 5% to target which is nearby skin. Overestimation of dose must be considered while deciding dose to critical structures which are at greater depths.
SU‐E‐T‐346: Dosimetric Evaluation of a High‐Dose‐Rate Modified‐Rotte “Y” Applicator for Treatment of Inoperable Endometrial Cancer
Authors: Esquivel C , Stathakis S , Eng T , Patel A , Gutierrez A , Mavroidis P , Papanikolaou N
Published: July 2013

Purpose: Evaluate dosimetrically the use of a modified Rotte Y‐tandem applicator for HDR brachytherapy treatment of endometrial cancer. Methods: For inoperable endometrial cancer or patients of morbid obesity, the use of a Rotte Y‐dual tandem applicator has been an integral part of treating patients with large uterine widths. Ten patient plans were selected to dosimetrically evaluate the use of a modified Rotte applicator. A third tandem was placed anteriorly and superiorly to the two lateral dual tandems inside the uterine cavity. Each patient fraction was scanned with 5 mm slice thicknesses and exported to the Oncentra v4.1 treatment planning system. A second plan was created with the use the dual‐tandem applicator only. The maximum doses to the bladder, rectum, sigmoid, and intestines were found for each plan. Dose volume histograms were created to evaluate the treatments delivered. Oncentra Plan Analysis module was use to compare both plans. Results: Using the dose volume histograms, the uterine dose coverage for one treatment was at 20% when the modified Rotte applicator was used. The plan with the unmodified, dual‐tandem applicator covered 12% of uterine volume. Doses to the structures of interest were higher when the modified Rotte applicator was used, but all were still well below their dose tolerances. Conclusion: The use of the modified Rotte applicator with a third tandem can be used to effectively cover large uterine widths for the treatment of endometrial cancer.
SU‐E‐T‐350: Investigation About Source of Errors in Treatment Planning of HDR Brachytherapy by Using a New Phantom Design Combined with Gafchromic Films and TG‐43 Calculation
Authors: Gholami S , Mirzaei H , Meigooni A , Jabariarfaei A , Mahdavi S , Blookat E , Ghorbani M
Published: July 2013

Purpose: GZP6 machine is used for high dose rate (HDR) brachytherapy treatment. In this project, treatment planning of GYN brachytherapy of this machine has been evaluated using a newly fabricated phantom along Gafchromic films and TG‐43 calculation. Methods: A new QA phantom has been designed and fabricated from 90 slabs of Perspex to accommodate ovoids assembly of GYN brachytherapy treatment. Two large oviods with 3 cm diameter was used for this assembly. EBT Gafchoromic films were exactly sandwiched between slabs and completely fitted to shape of ovoids for verification of GZP6 treatment planning. Plan designed to deliver 2.5 Gy dose to surface of oviods. The measured doses values at several points of interest were evaluated. The measured data were compared with the calculated values by the GZP6 treatment planning software. With seeing large difference between film dosimetry and planning, Air kerma strength (Sk) was obtained from Monte Carlo simulation and considered for TG‐43 calculation to reduce error. Results: The Result of these investigations have indicated differences of up to ± 23.4 % between the treatment planning and measured film dosimetry data at different points in GYN implant with GZP6 60Co HDR system. Between air kerma strength used in planning and Sk from simulation, 26% difference was calculated. TG‐43 calculation with simulated Sk can reduces difference between measurements to around 9%. Conclusion: The new phantom could be utilized for the QA procedure of the GZP6 60Co HDR system or the Ir‐192 HDR system to confirmation the accuracy of treatment planning in GYN implants and to find source of systematic errors.