bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐12: Development of a Software Tool for Investigation of Methods to Compensate for an Interrupted Radiation Treatment
Authors: Shokrani P , Danesh S , Hosseinabadi M Tavakoli
Published: November 2011

Purpose: When a prescribed course of radiation treatment is interrupted, the remaining treatment sessions must be altered. A number of compensation methods have been suggested in the literature. Some of these methods may not be accepted because of tumor underdosage, increased risk of reactions in organs at risk (OARs) and departmental policies. The goal of this research was to develop a software tool that enables the radiation oncology team to investigate available options and select the best method of compensation on an individual patient basis. Methods: Compensating methods differ in overall treatment time, number of compensating fractions and dose per fraction. For each method, we calculated biological effective dose (BED) and normal tissue complication probability (NTCP) of the OARs using the same tumor BED and tumor control probability (TCP) as the prescribed regimen. The suitable method was then selected as the method with the least increase in OARsˈ BED and NTCP. BED values were calculated using the linear quadratic model formalism. TCP and NTCP values were estimated using Tumorlet and Lyman‐Kutcher‐Burman models, respectively. The gap‐ compensation software developed in this research accepts differential dose volume histograms and gap information as input and uses the provided database to calculate BED, TCP and NTCP values for each compensation method. Results: The results indicate that while the change in BED relative to the intended BED does not depend on the gap position, it is strongly dependent on the type of tumor and OARsˈ tissue types: 13% for head and neck vs. 8.7% for prostate, and about 8.5% to 10% for normal tissues. Conclusions: A software tool was developed to allow for the selection of the best compensation method for interrupted radiation treatments. The method with the lowest change in BED and NTCP in comparison to intended program, is selected to substitute the original plan.
SU‐E‐T‐16: Use of Radiation Protraction for Target Dose Escalation
Authors: Kuperman V
Published: November 2011

Purpose: The main problem considered in our investigation can be stated as follows: are there any radiobiological advantages of intentionally increasing fraction time? Methods: By considering biologically equivalent doses to the target (BED1) and adjacent critical organ (BED2), we demonstrate that radiation protraction can be beneficial in the following sense: simultaneously increasing fraction time and monitor units can be used to maintain fixed BED2 while increasing BED1. In order to elucidate the obtained results, the considered approach is used to compare the effect of radiation protraction on step‐and‐shoot, prostate IMRT. Results: It is shown that radiation protraction can be used to increase BED1 under certain conditions for tumor and normal cells radio‐sensitivities, target and normal tissue fraction doses, and rates of sub‐lethal damage repair. Conclusions: radiation protraction can help increase BED to the target while maintaining fixed BED to the normal tissue.
SU‐E‐T‐17: Fractionation Effect on SBRT Using the Red Shell Concept and Linear Quadratic Model
Authors: Yang J , Lamond J , Fowler J , lanciano R , Feng J , Brady L
Published: November 2011

Purpose: The Red Shell is defined as the surrounding irradiated tissue that will be permanently damaged in SBRT. We examined the relationship of BED and fractionation on a small radiosurgical target, computed using multiple a/b ratios. Methods: A 2cm spherical target received a spherical radiation dose cloud with 10% fall‐off per 2mm from the center. Its Red Shell was defined as tissue that received at least a BED equivalent to 2Gyx30. First, we used a BED equivalent to 12.5Gyx4 for various tumor a/b ratios and fractionation schemes (1 to 10 fractions). Second, using a/b ratio of 10 Gy, various 3‐fraction schedules were plotted along with their corresponding BEDs from 1–10 fractions. Red Shell volumes were individually calculated to analyze the fractionation effect for different a/b ratios and prescription doses. Results: In the first set of calculations with a BED equivalent to that of 12.5Gyx4, an increase in fractionation was most beneficial in reducing the Red Shell volume when the a/b ratio was high. The greatest benefit was seen within the first few fractions. When the a/b ratio was low, an increase in fractionation was detrimental. With a/b ratio of 5.15Gy, all fractionation schemes had the same Red Shell volume. In the second set of calculations, the greatest Red Shell volume reduction with increased fractionation was seen with the lowest BED equivalent to 10Gyx3; the least volume reduction was seen with the highest BED. There was a detrimental effect to fractionation with the highest BED at 30Gyx3. For a/b ratios resulting in a BED equivalent to 28.7Gyx3, all fractionation schemes had the same Red Shell volume. Conclusions: Multiple interrelated factors, particularly a/b ratio and BED, affect Red Shell volume. Increased fractionation was not always beneficial, and was detrimental when the a/b ratio was low or if the BED was very high.
SU‐E‐T‐21: Repair of DNA Damage from Ionizing Radiation in the Range of Doses Experienced in CT Studies
Authors: Saxon S , McNitt‐Gray M , Ruehm S , Iwamoto K
Published: November 2011

Purpose: To quantify the kinetics of the cellular response to low, CT‐relevant doses of ionizing radiation (IR) in U87MG human glioblastoma multiforme cancer cells in vitro. Method and Materials:U87MG cells were irradiated with 0Gy (controls), 20mGy (in typical CT range), or 2Gy (exceeding CT dose range) using an X‐ray cabinet irradiator at 150kVp. The cellular kinetics of DNA damage and response were quantified by flow cytometric quantitation of H2AX foci at two time points (1hr and 6hrs post‐IR); using flow cytometry allows a much higher throughput than conventional methods. An auto‐fluorescence control was performed for each sample. Collected flow cytometry data, corrected for debris and dead cells using side and forward scatter gating, were analyzed with CellQuest Pro Software. Fluorescence histograms were generated for each sample and the respective auto‐fluorescence histogram was subtracted from each. The percentage of gated cells staining positive for H2AX (beyond an a priori threshold based on the IgG negative control) was determined. Results: In cells exposed to 2Gy, H2AX substantially increased within 1h and returned to control levels 6h post‐irradiation. In contrast, although cells exposed to 20mGy showed a measureable increase in H2AX formation within 1h, there was no significant decrease 6h later. Conclusion: Our results suggest DNA damage induced by low, CT‐relevant doses is repaired at a slower rate than damage induced by higher doses. This altered kinetic response could have marked biological effects for current radio‐diagnostic procedures. Our study, therefore, underscores the importance of understanding the different repair mechanisms at different dose regions in order to accurately assess risk estimates and biological dose. Future work will investigate longer observation times to assess DNA repair in more detail in the current cell model as well as in normal lymphocyte cell lines.

This work is partially supported by a SIEMENS Corporation research grant.
SU‐E‐T‐22: Improving Physicistsˈ Workflow with Electronic Logbooks
Authors: Goggin L , Chen J , Descovich M
Published: November 2011

Purpose: We present an electronic logbook, an efficient tool for tracking physicistsˈ work on treatment equipment in the clinic. Web accessible electronic logbooks have replaced their paper equivalents in many physics laboratories, particularly in high‐energy physics, as a more reliable means of tracking progress on projects involving a large number of people. In the radiation oncology environment there are several machines that need constant monitoring and frequent maintenance, and several physicists and engineers ensuring these tasks are successfully accomplished. Although paper records of such events are traditionally kept, these have several disadvantages: they are at risk of being misplaced, are only accessible in one place, can be cumbersome to search through, and all too often contain illegible handwriting. Methods: An electronic log, “elog”, (written by Stefan Ritt and released under the GNU Public license), was configured for the radiation oncology environment with the aim of improving physicistsˈ workflow and as a result, increasing patient safety. Entries are made on a webpage, submitted to a database, and assigned a URL that is linked from the logbook homepage. Entries may include formatted or plain text, tables, images, and attachments. Examples of use include machine maintenance records, discussion of machine‐specific issues, and routine quality assurance results. Results: This free software is very user‐friendly; a prototype electronic log was successfully configured for the UCSF clinic in a matter of days, and a demonstration of its use was made. The elog is currently being implemented for use in the CyberKnife suite and to track issues with treatment planning computers. Conclusions: The elog has the potential to improve workflow, encourage accountability, increase accessibility of information, and promote discussion of treatment machine specific issues. This may result in a safer and more effective patient experience.
SU‐E‐T‐23: Ontological Representation of Radiation Treatment Guidelines
Authors: Ge Y , Minta T , Kirkpatrick J , Yuan L , Wu Q
Published: November 2011

Purpose: To develop a Radiation Treatment Guidelines Ontology (RTGO) that represents the concepts, knowledge, and guidelines in radiation therapy using a formal and computable framework. This ontology will serve as the foundation of a decision support system for radiation oncologists. Method and Materials: The ontology framework chosen to represent RTGO is the Web Ontology Language (OWL) (www.w3.org/TR/owl‐guide). The OWL is rooted in the rigorous foundation of Description Logic and represents the latest development in ontology languages. The Protégé‐OWL ontology editor and knowledge‐base framework (http://protégé.stanford.edu) is used to build the ontology. The ontology is developed in a multi‐layered, modular, and iterative fashion. Upper ontologies are used to provide a sound structure. Concepts from standard ontologies are adopted whenever possible. Salient concepts and relationships are incorporated into the ontology through multiple iterations of extraction, modeling, implementation, and evaluation. Each iteration examines increasingly detailed concepts and relationships. The concepts are asserted in a strict subsumption hierarchy and are carefully formulated to be at a proper level of abstraction consistent with anticipated questions addressed by the ontology. Major ontology resources used in this project include National Center Biomedical Ontologyˈs Bioportal (bioportal.bioontology.org) and National Library of Medicineˈs Universal Medical Language System (UMLS) (www.nlm.nih.gov/research/umls). Major ontologies consulted include FMA for anatomical concepts, SNOMED for clinical findings and symptoms, and Semantic Network for relationships. Results: The initial focus is on modeling the concepts and knowledge summarized in the Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) papers. Starting with the organ specific papers on bladder and rectum, the ontology has so far captured 171 concepts, 80 relationships, and 21 individuals. The development is proceeding to include other organs in the QUANTEC literature. Conclusion: Early results demonstrate that major concepts in QUANTEC papers regarding dose volume effects can be successfully captured in an ontological framework.

Duke University has a Master Research Agreement with Varian Medical Systems, INC.
SU‐E‐T‐24: Remote, Automated Daily Delivery Verification of Volumetric Modulated Arc Therapy Treatments Using a Commercial Record and Verify System
Authors: Fontenot J , Gibbons J
Published: November 2011

Purpose: Volumetric modulated arc therapy (VMAT) is an effective but complex technique for delivering radiation therapy. VMAT relies on precise combinations of dose rate, gantry speed, and multi‐leaf collimator (MLC) shapes to deliver intensity modulated patterns. Such complexity warrants the development of correspondingly robust performance verification systems. In this work, we report on the feasibility of using data collected from a commercial record and verify system to perform remote, automated daily delivery verification of volumetric modulated arc therapy (VMAT) treatments. Methods: The performance verification software system consists of 3 main components: (1) a query module to retrieve daily MLC, gantry, and jaw positions reported by the linear accelerator control system (Elekta, Crawley, UK) to the record and verify system (Mosaiq, Elekta, Mountain View, CA, USA), (2) an analysis module to read the daily delivery report generated from the database query module, compare the reported treatment positions against the planned positions, and compile delivery position error reports, and (3) a reporting module to display graphical reports initiated by a user or to automatically alert authorized users when pre‐defined tolerance values are exceeded. The utility of the system was investigated through analysis of patient data collected at our clinic. Results: Nearly 2,500 VMAT fractions have been analyzed with the delivery verification system at our institution. The average percentage of reported MLC leaf positions within 3 mm, gantry positions within 2 degrees and jaw positions within 3 mm of their planned positions was 92.9 +/− 5.5%, 95.9 +/− 2.9%, and 99.7 +/− 0.6%, respectively. The level of agreement between planned and reported MLC positions decreased for treatment plans requiring larger MLC leaf movements between control points. Conclusions: The delivery verification system holds the potential to provide an effective and low‐cost quality assurance tool that improves patient safety.
SU‐E‐T‐27: An Ontology‐Based Framework for Radiation Oncology Patient Management
Authors: McShan D , Kessler M , Fraass B
Published: November 2011

Purpose: To describe the benefits of the use of an ontology (a semantic description of concepts, properties, and relationships) as the base of a data management system which provides the (often missing) connecting information regarding goals and process used for patient management. Method and Material: The ontology has been defined with an OWL ontology model using Protégé and Oracle. The ontology database consists of the ontology model and the instances (actual data). Supporting code which forms the distributed components is written in Java, C, C++,and Fortran. Messaging between components uses an open‐source AMQP broker. To retrieve and update data, SPARQL queries are messaged to the ontology access components. Results: Initial ontology construction has been based on standard and departmental concepts. Guidelines used include making the ontology of sufficient (and extensible) scope to tie together key concepts with enough depth to be useful for study retrieval (queries), and with enough attribution to identify related source material (files, URLs, other databases, PACS…) when additional detail is desired. Integration of this new knowledge‐modeling mechanism into our clinical/research infrastructure framework is underway. Current efforts focus on modeling and implementing more sophisticated management of planning and delivery for adaptive therapies based on biomarker assessments that identify or predict changed response to the dose received during treatment. In these complex protocols, treatment plans must be organized by treatment directives that specify treatment goals, must include detailed knowledge of prior treatment, and manage all new patient‐specific data acquired during the treatment course. Conclusions: An ontology‐based knowledge base has been developed as the information framework of a new treatment planning and workflow management system. This ontology provides the extensible means to describe and manage highly complex adaptive treatment protocols for unique and advanced clinical studies.

Supported in part by NIH grant CA‐P01‐59827
SU‐E‐T‐28: Task Tracking and Messaging for Workflow Optimization of Treatment Planning Process
Authors: Kantor M , Kanke J , Dong L
Published: November 2011

Purpose: The entire radiotherapy treatment planning process, from simulation, target definition, planning, to treatment, requires a collaborative effort from a multidisciplinary team of highly specialized professionals. Although treatment planning is a highly sequential process for an individual patient, professionals are consistently multi‐tasking to support on‐going patient care activities. As a result, treatment planning is a lengthy process, which often results in delay of new treatment start or poor quality treatment plans. Methods: To improve accountability and optimize workflow, a novel electronic messaging solution using event triggering and automatic information processing was designed to improve the effectiveness of collaboration among different professionals for treatment planning. In order to reduce the burden of data entry, we have made efforts to develop software interfaces to other clinical systems, such as the electronic medical record (EMR), integrated scripts executed in the planning system, or Active Directory to obtain plannerˈs information. Professionals receive e‐notice from the system immediately following the completion of the previous step. Results: In our initial deployment of the system clinical wide, the system tracked 2500 planning assignments in the main campus and regional cancer centers with 50+ practicing radiation oncologists and approximately equal numbers of dosimetrists and physicists. The system provided an electronic media to communicate with physicians, dosimetrists, and physicists to improve communication on prescription, dose tolerance, or just simply the timeline for the planning activities. The average simulation‐to‐treatment start time was 3 business days in 50% patients, but IMRT took extra 2 business days to complete. IMRT contouring was completed in one business day in 72% of patients. Workflow bottleneck was identified in certain services for which dominant Monday new starts and rushed plans on Friday were observed. Conclusions: We designed a novel workflow enhancement tool to assist collaboration and process improvement.

Research partially supported by Philips Medical Systems
SU‐E‐T‐29: Workflow and Data Architecture Paradigm for Building a Large Scale Dose‐Volume Registry
Authors: DeMarco J , Low D , Wang J , Kupelian P
Published: November 2011

Purpose: In support of a robust outcome registry initiative, we present a workflow and architecture design for an efficient dose‐volume registry module. Methods: The UCLA Radiation Oncology registry management system is composed of two separate database modules; a SQL‐based patient attribute module and a dose‐volume module that is defined based upon two data structures; data_tech and data_dose. The data_tech object defines site‐specific, technical treatment details referenced to a patient identifier. The data_dose object connects with the data_tech object using the patient identifier as a primary key. Each contour in the data_dose object is defined based upon standard dose‐volume endpoints and assigned a structure index referenced to an anatomy dictionary. The patient index key connecting the data_tech and data_dose objects provides for aggregate dose‐volume analysis as a function of treatment details and anatomical index. Results: Upon physician approval of a particular treatment plan, the planning dosimetrist or physicist exports the dose‐volume data for long term storage and updates the data_tech object with the relevant planning and treatment delivery parameters. A MATLAB interface was developed and tested with the Eclipse planning system to read all applicable dvh export files and create the two‐dimensional data_dose object. A second MATLAB module processes the data_tech and data_dose objects to perform aggregate processing and statistical analysis of the data. We have tested the module design using a subset of prostate, H&N and breast treatment plans. The integer indexing scheme allows for efficient queries across a mixed group of dose‐volume structures and site‐specific treatment parameters Conclusions: The indexing architecture associated with the data_tech and data_dose registry modules provides an efficient method for extracting subset parameters from the complete data set. Future work will connect the dose‐volume registry with the SQL‐based patient outcome module to allow for outcome analysis as a function of treatment and dose‐volume details.
SU‐E‐T‐30: National Radiation Oncology Registry: Concept to Design Specification
Authors: Le A , Kapoor R , Palta J
Published: November 2011

Purpose: To present the design and system architecture of the National Radiation Oncology Registry (NROR) to electronically collect aggregated data on cancer patients treated with radiotherapy with the goal of evaluating comparative effectiveness of competing radiotherapy treatments, outcomes, “patterns of care”, gaps in quality, safety, and cost. Methods: The design requirements include a secure automatic upload and archival of anonymized patient data, a web‐based upload/download tool for reviewing the collected data in a distributed database environment. The system design and architecture utilizes Web‐based technology and current available commercial products to automatically abstract dosimetric parameters from the treatment planning systems and outcome parameters from clinician reported outcome (CRO) portal, patient reported outcome (PRO) portal, and radiotherapy electronic medical record (RT‐EMR) systems. A centralized NROR Server would contain interfaces, templates and data dictionary, allowing integration of all collected patient data into a centralized data base and would provide a web ‐based tool to manage, review and analyze these data for outcome and competitive effectiveness research (OCER). Results: The design and system architecture is ready for implementation. A pilot registry of prostate cancer patients treated with different modalities of radiation treatments is planned to test the electronic infrastructure for registry data collection. The system will be initially deployed at a limited number of volunteer institutions (approximately 20) to test the concepts and sustainability of the NROR. These institutions will be selected in such a way that they represent a population‐based sample for OCER. Conclusions: The establishment of the National Radiation Oncology Registry will be of great benefit to treating radiation oncologists and other care providers, payors, vendors, policy‐makers and most importantly cancer patients by capturing reliable information on population based treatment delivery and health outcomes.
SU‐E‐T‐31: Development of a Radiation Oncology Patient Flow Dashboard System
Authors: Yeung I , Gallamore M , Moseley D
Published: November 2011

Purpose: To develop a dashboard for tracking patient treatment plans going through different stages in treatment planning process. Methods: The stages from ‘decision to treat’ to ‘treatment complete’ and the software systems associated with these stages in the treatment planning process were identified. The steps of the treatment planning process that were tracked by the dashboard system was the ‘decision to treat’, ‘CT simulation’, ‘contouring complete’, ‘plan publish’, ‘plan approval’, ‘treatment start’ and ‘treatment end’. The systems where this information was extracted included the booking system (eBooking), treatment planning system (Pinnacle), treatment plan review system (WebPublishing), and record and verify system (MosaiQ). The flags for different activities and the time stamps associated with these activities were extracted from these systems via text file reports in the case of Pinnacle and MosaiQ, and ODBC connections to the database for real‐time data gathering from eBooking and WebPublishing. A web‐based dashboard display was developed to provide the status of all treatment plans going through the process and whether the milestones are reached as being on schedule (green), close to deadline (yellow) or overdue (red). Results: A web‐based display dashboard has been developed to provide the status of each treatment plan going through the treatment planning process. The information was able to reflect the stress points in the system and enable management and front line workers to respond to these stress points by proper allocation of resources Conclusions: The Radiation Treatment Dashboard System provided a tool to monitor treatment plans through the treatment planning process. It could be an invaluable tool for the management of a medium to large size facility to maintain an evidence‐based treatment planning operation. It can also potentially expand to other aspects of the radiation treatment program.
SU‐E‐T‐34: Time Series Analysis of Skin Reactions during Heck and Neck IMRT
Authors: Glennie D , Doerwald‐Munoz L , Ostapiak O , Patterson M , Hayward J , Farrell T
Published: November 2011

Purpose: To quantitatively characterize the time sequence of skin erythema in head and neck patients undergoing intensity modulated radiation therapy (IMRT) treatments using optical reflectance spectroscopy. The overall goal is to identify patients who will develop extreme skin responses earlier than is possible by visual inspection alone. Methods: Ten (10) patients undergoing IMRT for the treatment of head and neck cancers were followed throughout the course of their intervention. Daily spectral skin reflectance measurements were made in order to track changes in the tissue optical properties. Weekly thermoluminescent detector (TLD) readings were performed in the measurement area to verify the dose calculated by the treatment planning system. Patients also completed a weekly questionnaire on factors that may have affected their skin reaction, and were visually inspected by a radiation oncologist.Results: The data were fit by a 2‐component principle component analysis (PCA) model. The preliminary results show that absorbed dose is the largest contributor to changes in the spectral reflectance and that those changes are seen primarily at wavelengths above 600 nm. Differences among patient skin responses were seen and accounted for in the model Conclusions: The PCA model indicates that it may be possible to predict a patientˈs spectral skin reflectance measurement on the final day of treatment given an initial spectrum and the dose. Therefore, further analysis of the data may yield a method of determining patient reactions before visible signs are detected.

Partial funding through Varian, Inc. and the Natural Sciences and Engineering Research Council of Canada.
SU‐E‐T‐37: A New Metric to Predict Rectal Bleeding Based on Dose‐Surface Properties
Authors: Lee R , Liu M , Moiseenko V
Published: November 2011

Purpose: To test a new property that can be used as an effective prognostic indicator of rectal toxicity against rectal bleeding data in prostate cancer patients. Methods: The method is based on dose to surface and accounts for spatial relationship between rectal surface elements. A property that is a function of the dose at 2 points on the rectal surface weighted by a function dependent on the distance between the points is proposed as an alternative to DVH criteria for predicting rectal toxicity. The weighting function was described as a logistic function. The shortest distance between the points i and j on the rectal surface was approximated using the multistencil fast marching method (MFMM). This approach approximates a solution to the Eikonal equation which describes the propagation of an advancing wavefront from a source point, i. Then, the distance between any points, i and j, can easily be determined if the speed is constant. For each patient the maximum value of the property calculated for all surface elements is considered as a candidate for predicting rectal bleeding. The property was calculated for 170 patients who underwent external beam radiotherapy for prostate cancer and followed‐up for rectal bleeding. The prognostic value of the property was evaluated using log‐rank test for actuarial incidence of complications. A range of logistic function parameters was considered. Results: Eighty seven cases using various combinations of the constants that control the slope and inflection point of the logistic function have been processed. The maximum value of the metric spanned a range from 32.37 to 599.8 (Gy·cm)̂2. The analysis for the prognostic power of the property is in progress. Conclusions: The proposed rectal surface property incorporates dose as well as spatial relationship between rectal surface elements. It is easily calculated for an arbitrarily complex geometry.
SU‐E‐T‐38: Validating the Use of a New Tumor Irradiation Quality Metric for Lung and Head and Neck Tumors: Total Clonogen Survival
Authors: Zuniga AA , Thorstad WL , Oh JH , Apte AP , Bradley JD , Deasy JO
Published: November 2011

PURPOSE: Ideally, a single factor would allow objective ranking of dose distributions with respect to the probability of local control. The purpose of this work is to study the applicability of a new metric as a predictor of local control (LC) indicator in head and neck tumors and lung tumors. MATERIALS: Two datasets were used: (A) 80 head and neck (H&N) patients using IMRT, and (B) 56 non‐small cell lung cancer who received 3D conformal RT both treated at Washington University in Saint Louis at standard fractionation. 23 H&N and 22 lung patients failed locally. A simple model was used to derive the expectation value of the number of surviving clonogens per initial clonogen density (not initial number). Other dose‐volume parameters were compared to TCS. Correlation with LC for univariate and multivariate logistic models of the available parameters was assessed using the area under receiver operating characteristic curve (AUC) and Spearmanˈs rank correlation coefficient (Rs). We also tested bootstrap cross‐validation of the models. Results: Total Clonogen Survival was the most predictive variable on univariate analysis in both datasets using an optimal value of SF2=0.8 ((A) Rs=0.444 p‐value<0.0001 (B) Rs=0.441 p‐value<0.0001). In logistic regression for both datasets, all statistically significant multivariate models included TCS parameter. Multivariate logistic regression for (A) shows that a two parameter (TCS and stage_group) model was the most significant when cross‐validated (RsCV=0.4644, pCV‐value=0.02). Higher order models did not appear more predictive after cross‐validation. However, we report in an abstract at this meeting that machine learning using TCS can improve predictive power. Conclusions: TCS was shown to be a simple and useful parameter when predicting LC in these two datasets. It differs from cell‐kill based EUD by mechanistically accounting for tumor volume variation.

Partially supported by NIH R01 grant CA85181.
SU‐E‐T‐41: Measurement and Modeling of the Gross Tumor Volume Shrinkage of Lung Tumors as a Function of Delivered Therapeutic Dose
Authors: Ali I , Algan O , Ahmad S
Published: November 2011

Purpose: To measure quantitatively in‐vivo shrinkage of gross tumor volume (GTV) using CT imaging and model GTV as a function of delivered dose during treatment. Methods: The GTV of three selected non‐small cell lung tumors were outlined on CT images acquired weekly during treatment course with regular fractionated regimens of 180 cGy over 35 fractions. These patients have well defined lesions in the middle of the lung where the GTV has high contrast compared to lung and other tissues. The GTV variations were measured as a function of delivered dose. Then, GTV‐dose curves were fitted with three exponential functions with linear and linear‐quadratic dose dependence that decreases to zero or certain residual volume levels. Results: The GTV shrinks exponentially as a function of dose through the treatment course. However, the GTV does not decrease to zero volume by the end of treatment. Among the three different formulas used to fit the GTV‐dose data, it was found that the exponential function that decays linearly with delivered dose to a certain volume level provides the best fitting formula of the GTV shrinkage. Alpha obtained from non‐linear curve fitting of the three patients varied by less than a factor of 2. The normalized residual volumes were within a factor of 3 and was not influenced by the initial GTVˈs which varied by more than a factor of 20. Conclusions: Neither a simple exponential function with a linear dose decay nor a complicated exponential function with linear‐quadratic dose decay, fit well GTV response as a function of dose through the treatment course. The linear exponential decay function to non‐zero volume level provided the best fitting formula to GTV‐dose data. This might be due to the necrotic core of the tumor that is less responsive to radiotherapy.
SU‐E‐T‐109: Evaluation of the Stability of the Central Axis Response of An Amorphous‐Silicon EPID Used in the Continuous Mode of Image Acquisition
Authors: Vazquez‐Quino L , Fitzpatrick M , Alkhatib H , Mavroidis P , Papanikolaou N
Published: November 2011

Purpose: To investigate the stability of the central axis (CAX) response of an amorphous‐silicon (a‐Si) EPID in continuous mode as function of the number of frames per image and the dose rate of dose delivery. Methods: The Varian aS1000 amorphous‐silicon EPID (PortalVision, Varian Medical System, Palo Alto, CA) fixed to a Novalis TXTM (Varian Medical System, Palo Alto, CA) is used in this study to investigate the CAX of the EPID with time. The continuous mode of acquisition is capable of acquire a sequence of multiple images in real time during radiation is being delivered. A 10×10 cm2 field is imaged by an onboard EPID imaging system for 100 MU using the continuous mode acquisition varying the number of frames (frame rate) contributing each image. The source to detector distance (SDD) in fixed at 110 cm for all measurements. Accelerator output is imaged for dose rates of 600 and 300 MU/min. The frame rate is varied from 1 to 10 frames contributing to each image. The rate is approximately 7.5 frames per second. The EPID images were analyzed using an in‐house routine developed in MATLAB V7.8.0347 (The Mathworks. Inc), this consists in evaluates the response of a central region of the images which consist of 50×50 pixels in the central axis region. Results: After the analysis of the images the results show a period of over‐response followed by a period of under‐response during the first 2 seconds of the irradiation. After 3 seconds EPID response settles to nearly constant value. The phenomenon is nominal behavior for a linear accelerator. Conclusions: This works shows that the central axis response with time for an a‐Si EPID using the continuous mode of acquisition is accurate to ∼1/7 of a second.
SU‐E‐T‐110: Quantitative Image Based Measurement of Electron Beam Spot Position
Authors: Nyiri B , Smale J , Gerig L
Published: November 2011

Purpose: Develop an image based method to measure electron beam spot position w.r.t the Collimator Axis Of Rotation (CAOR). Methods: Two stainless steel rods, 3 mm in diameter, are mounted in a jig attached to the linac collimator. The rods lay in different planes normal to the CAOR, one at 159 cm SSD and the other at 70 cm SSD, and are offset 10 and 6 cm from the CAOR respectively. Images of both rods are acquired at multiple coll rotations. At each angle the rods project a tangent to an inscribed circle, the centre of which is calculated. The lower rod is very close the plane of the EPID and the centre of its inscribed circle defines the mechanical CAOR. The centre of the inscribed circle calculated from multiple images of the upper rod will be displaced from the CAOR by some distance proportional to the distance the beam source is from the CAOR. Test measurements were performed on an Elekta 6 MV where the In Plane beam spot position was moved a known distance using steering fine and beam spot position was measured.Results: Independent beam spot measurement (Flexmap Image Registration ball bearing) reported the initial beam spot at 0.29 mm from CAOR, moving to 0.91 mm (delta =0.62 mm) with steering. The rod tests showed the initial beam spot to be .31 mm from the CAOR and 1.17 mm from CAOR after adjustment. Note that in our companion paper we report similar values (initial 0.13mm going to 0.92 mm and initial value of 0.09mm going to 0.79) with our two co‐rotational dosimetric beam spot tests Conclusions: A simple method for measuring beam spot position with respect to CAOR is described. It provides its own internal reference and could be incorporated into routine QA using the EPID.

Jason Smale is an employee of Elekta Canada
SU‐E‐T‐111: Radiochromic Film Measurements of Small Field Surface Doses from Flattened and Unflattened 6MV and 10MV Beams
Authors: Clift C , Mynampati D , Yaparpalvi R , Mah D
Published: November 2011

Purpose: To measure surface doses from small fields from flattened and unflattened 6MV and 10MV photon beams using radiochromic film.Methods: GAFCHROMIC EBT2 film was used in a solid water phantom to make surface dose measurements from photon beams generated by a Varian TrueBeam Stx linac. Four energies were included: 6MV and 10MV, as well as two corresponding flattening filter free beams (6FFF and 10FFF). The field sizes considered where 10, 5, 4, 3, 2, 1 cm2. One 3×3 cm piece of EBT2 film was irradiated at the surface and at dmax in a solid water phantom for every energy and field size. Films were also placed at dmax and irradiated to obtain a calibration curve. All films were scanned in an EPSON V700 flatbed scanner and analyzed according to established protocols using in‐house developed software. Results: The measurements of surface dose for each field were normalized by the dose measured at dmax. Surface doses ranged from 10% for a 1 cm2 6MV field to 25% for a 10 cm2 6MV field. The ranges for other energies were 16–33%, 5–17%, and 10– 17% for 6FFF, 10MV, and 10FFF, respectively. As expected, the surface dose for both 6MV and 6FFF fields are higher than surface doses from 10MV and 10FFF fields. The surface dose relative to dmax is shown to be a monotonically increasing function of field size. Unflattened beams exhibit a higher surface dose in comparison to flattened beams and this discrepancy is larger for 6MV and 6FFF fields Conclusions: This work makes use of a simple technique for measuring surface doses from small fields relevant to SRS and SBRT, taking advantage of the high resolution offered by radiochromic film. The surface dose measured for a range of standard and small field sizes for flattened and unflattened beams has been presented.
SU‐E‐T‐113: Measurement of the Cutout Output Factor on Ortho‐Voltage Unit Using EBT‐2 Model GafchromicTM Film
Authors: Liang L , Tomic N , Devic S , Seuntjens J , Deblois F
Published: November 2011

Purpose: In this study, we evaluate feasibility of using EBT‐2 model GafchromicTM film to measure patient specific cutout output factors on an ortho‐voltage treatment machine. Methods: A Gulmay Orthovoltage D3225 unit was used to produce clinical beams in kV range from 50 kVp to 220 kVp. Previously established air kerma based radiochromic film dosimetry protocol for low energy x‐ray beams was used. A closed‐end applicator with 10 × 10 cm2 field size and SSD 50 cm was employed. Cutouts were made from a lead sheet of 1.8 mm in thickness. A 6‐cm thick slab of Solid WaterTM was used as a backscatter material for output factor measurement. In‐house made MatLab routines were used to analyze scanned images of exposed and unexposed films and a PTW 23342 parallel‐plate ion chamber (PP IC) was used to measure the cutout output factors for comparison. Results: Air‐Kerma based calibration curve was created in the 1–300 cGy range. Film dosimetic accuracy was verified for known doses to water of 1.00 and 2.00 Gy, respectively, with maximum observed difference of 0.4%. Two‐dimensional dose maps and dose profiles were obtained for various cutout sizes ranging from 0.8 cm diameter circle to 10 × 10 cm2 square. Comparisons of output factors between film and pp ion chamber measurements show that there are no differences for large cutouts but the chamber measurements are up to 11 % higher for small cutout size. Conclusions: We demonstrated that the air‐Kerma based radiochromic film dosimetry protocol using EBT‐2 model GafChromicTM film for low energy x‐ray beam is adequate for patient specific cutout output measurements on orthovoltage units, especially for small size cutout measurements, where IC measurements give higher output factor than films due to ICˈs over responses to electron contaminations from lead sheets.
SU‐E‐T‐114: Intercomparison of Stereotactic Scanning Diodes for Small Field Dosimetry
Authors: Yeager C , Hasson B , Sullivan P , Hand C
Published: November 2011

Purpose: As the approach to treating diseases is requiring the use of small fields for more complex treatments, the accuracy and consistency of the measurements of small fields is critical. The Sun Nuclear Edge Detector and the stereotactic diode (SFD) by IBA provide a small collecting volume that reduces the field perturbation seen with standard detectors. This work focused on the intercomparison of the Edge detector and the IBA stereotactic diode for measuring the dosimetric properties of small fields. The MapCheck2 device was also tested as a quick check for standard quality assurance tests. The small fields analyzed were generated from a Radionics mini‐multileaf collimating system. Methods: Scans were taken on the Siemens Primus linear accelerator for a 6 MV beam, set at 100 cm SAD and a depth of 5 cm, using field sizes ranging from 0.4cm × 0.4cm to 4cm × 4cm. Tissue‐phantom ratios were measured at 100 cm SAD, normalized to a depth of 4 cm for comparison between detecting systems. Data analysis was done using Matlab software to obtain the FWHM and penumbra for each scan. Results: The Edge and SFD detectors are consistent, with the largest difference seen at the smallest field size. The FWHM measured with theSFD was consistently smaller than those found with the Edge detector. A sharper penumbra was seen with the SFD at the smallest field size. There was more variation with the MapCheck2. The TPRs were consistent between detecting systems. Conclusions: The Edge and SFD detectors provide consistent measurements. However, at the smallest field sizes, the SFD detectorˈs small active volume and physical size perturb the dosimetric properties of the field to a lesser extent. The MapCheck2 device is sufficient for measuring outputs and TPRs, but more work must be done to conclude whether it is sufficient for scanning.
SU‐E‐T‐122: Effect of Refraction on Dose Reconstruction in Optical‐CT Gel Dosimetry
Authors: Florescu L , Ambartsoumian G , Wuu C
Published: November 2011

Purpose: Optical‐CT gel/radiochromic dosimetry has emerged as a promising candidate for 3D dose verification. One factor that affects the accuracy of dose reconstruction in this technique is the refractive index mismatch between the gel phantom and the matching liquid that prevents the full width of the phantom from being used for dose mapping. The purpose of this study is to investigate the effect of the refractive artifact on dose reconstruction, and to identify optimal designs for accurate gel dosimeters. Methods: Numerical experiments were carried out for a series of model attenuation coefficients of the gel phantom and various degrees of refraction resulting in situations where only projections through certain central sections of the sample are detected. Measured data was obtained as the Radon transform of the model attenuation coefficient. The attenuation coefficient was then reconstructed using the filtered backprojection algorithm. A mathematical study was performed in the framework of the so‐called interior problem of Radon transform inversion. The variation of the amount of data accessible experimentally with the refractive index mismatch was investigated using geometrical optics. Results: It was demonstrated that the reconstruction of the attenuation coefficient within 3% is possible in the central part of the phantom even if only 82.5% of the optical projections are detected. This fraction of available data results from a 1.5% refractive index mismatch between the gel and liquid. Using a priori knowledge of the value of the absorption coefficient at a given point in the sample, it is possible to calculate the correct value at all points. Conclusions: Optical attenuation and dose in an optical CT gel dosimeter can be reconstructed accurately in the central part of the dosimeter even if only limited data are available. A priori knowledge of the attenuation coefficient at a point in the sample enables almost exact reconstruction.
SU‐E‐T‐125: VMAT Monthly Quality Assurance Using a 2D Ionization Chamber Array
Authors: Myers P , Buckey C , Mihailidis D , Mavroidis P , Esquivel C , Gutiérrez A , Papanikolaou N , Stathakis S
Published: November 2011

Purpose: Periodic quality assurance is essential for the accurate and consistent operation of dynamic multileaf collimators (DMLC) for volume modulated arc therapy (VMAT). Varian RapidArc is a system for delivering VMAT that can vary gantry speed and dose rate as the DMLCs quickly change position in order to obtain a conformal dose. A more time efficient and reproducible method for verifying the RapidArc capabilities has been developed building upon previous work by Ling et. al. using a 2D ionization chamber array. Methods: The PTW seven29 2D‐ARRAY was used in conjunction with an isocentric gantry mount, removing directional dependence, to complete three tests. Tests included evaluating machine performance while varying dose rate and gantry speed, while varying DMLC speed and the dose rate, and DMLC position accuracy. Reproducibility of each test was also evaluated. Results: Dose rate (111–600 MU/min) and gantry speed (5.5–4.3 degrees/s) capability was studied with a RapidArc picket fence pattern consisting of 7 different sections of combinations and compared to a corresponding open field and was found to agree within 0.84%. DMLC speed (0.46, 0.92, 1.84, and 2.76 cm/s) evaluation was performed similarly and agreed within 3.66% (2.93–3.66%). A RapidArc picket fence was compared with a static gantry picket fence to evaluate DMLC position accuracy to within 2.91%. Reproducibility of each of the three RapidArc tests was found to be within 0.57%, 1.78%, and 2.70% respectively. Conclusions: The seven29 detector was able to perform the RapidArc quality assurance tests efficiently and accurately and the results were reproducible. Periodic verification of DMLC movement, dose rate variation, and gantry speed variation relating to RapidArc delivery can be completed in a timelier manner using this equipment.

This work partially supported by PTW, Freiburg, Germany.