Physics QA Research Articles

163 Enhanced Collaboration in Physics QA for Radiotherapy in Japan: The Hiroshima Model

163 Enhanced Collaboration in Physics QA for Radiotherapy in Japan: The Hiroshima Model

Multidisciplinary Institutional Guidelines for Workflow Efficiency in Optimizing Patient Start Time.

Radiation Oncology is a field which is reliant on the intradisciplinary team and efficient completion of respected tasks. The purpose of this study was to analyze institutional workflow efficiency by comparing current practices to team-member expectations. To measure workflow efficiency, the Aria database was queried to find sessions for treatment plans with a CT Sim image and a first treatment date between 2/23/2021 and 12/15/2022. The course, plan, prescription, image series, the associated "Provider Contouring" task, and the most recent consult appointment prior to the sim date were used to determine various workflow times using business days: (1) Consult to Sim, (2) Sim to Contour, (3) Contour to Plan, (4) Plan to Physics QA, (5) Physics QA to First Treatment. For these items, except for (3) Contour to Plan, the time points used to determine when a task was completed was based on timestamps of the actual work done rather than the associated task completion timestamp. For contouring, the completion timestamp was used. Additionally, for each treatment plan, a workflow category was assigned based on the prescription site and technique, the course and plan intents and IDs, and the activity code for the treatment associated with the session assigned to the plan. Regarding the objective analysis from the various personnel within the intradisciplinary team, an internal survey was conducted analyzing what each member of the intradisciplinary team deems as appropriate timing for task completion. The mean time from simulation to treatment start for palliative treatment was 3.67 days (306 treatment plans). For definitive 3D and IMRT plans, the mean simulation to treatment time were 7.85 and 9.71 days, respectively (200 3D and 261 IMRT treatment plans). Mean time for lung SBRT plans were 11.98 days (65 plans). Survey analysis within the intradisciplinary team for appropriate timing of palliative treatments were as follows: Physicians: 5.88 days, Dosimetrists: 1.25 days, Radiation Therapists: 1.31 days, Nursing: 3.25 days. Survey analysis of definitive 3D and IMRT plans were as follows: Physicians: 10 and 10.5 days, Dosimetrists: 3 and 6 days, Radiation Therapists: 3.75 and 5.75 days, Nursing: 8.5 and 8.5 days, respectively. Survey analysis of lung SBRT simulation to treatment demonstrated: Physicians: 12.5 days, Dosimetrists: 6 days, Radiation Therapists: 6.75 days, Nursing: 9.25 days. Analysis of our internal workflow demonstrates efficiency in total time from simulation to treatment across various modalities when compared to published data. Interestingly, when comparing our current workflow efficiency to team member expectations, there are discrepancies in the analysis of the definitive 3D and IMRT as well as lung SBRT. These variations may be due to the interdisciplinary team not having a complete understanding of the various workflow responsibilities of other team members.

Automatic organ contour check: One essential step in autonomous treatment planning.

Geometric and nomenclature errors are commonly encountered in automated treatment planning. We describe a novel algorithm to extract organ geometry relationships from patient structure DICOM data to construct a database that can be used to detect organ contour inaccuracies including relational and naming errors. Twenty-five sets of head and neck patients' treatment plan data (CT, structures) were retrospectively retrieved from our institution. For each dataset, various organs were contoured and verified by experienced physicians. The relative position and orientation between organs were extracted from each patient and the data were used to construct an organ relationship database model. The model was tested using a dataset originating from an in-house organ renaming software that often-introduced organ contour naming mismatches. As part of the validation test, the renamed organs relative positions were compared with the database model to identify mismatches. Within the forty head and neck patients, we extracted the geometric relationship between 201 organ pairs. The average number of unique types of organ pairs (for example, left parotid with left eye is one type of organ pair) stored in the database was 12. Fifteen head and neck structure sets automatically renamed using our in-house organ renaming tool was used as validation data. All of the 30 random assigned wrong name labels present in these structure sets were identified using the established organ geometry relationship database. We successfully constructed a head and neck organ geometry relationship database and validated it in a contour naming quality assurance process. This novel scheme can be expanded to the entire body and shows a great potential in automatic plan physics QA procedure. It should be one essential QA step in an autonomous treatment planning process.

Needs and Strengths Assessment for Radiotherapy Centers in Africa Transitioning to IMRT

Multiple centers globally are interested in implementing intensity-modulated radiotherapy (IMRT) programs, however little data exists comparing granular center-specific needs and strengths of radiotherapy (RT) centers interested in establishing an IMRT program, in low-resource countries in this position. In conjunction with up-scaling training, methods are needed to assess multiple centers efficiently. Using a novel approach, we assess centers' needs and strengths to tailor a multi-institutional remote training program.To assess strengths and needs of centers interested in establishing an IMRT program. Core RT leaders from 16 RT centers in 7 African countries (Ghana, Ivory Coast, Kenya, Nigeria, Senegal, Morocco, Zambia and one sister center in Pakistan) were individually invited to complete a 30-minute, 55-question electronic survey followed by 60-75-minute video conference with 2-4 lead members of a non-profit global health radiation oncology organization prior to participating in a remote IMRT training program.14 centers responded and were surveyed, and interviewed, including 11 public, 3 private and 1 hybrid institutions. Among centers 4 (28.6%) and 1 (7.1%) are currently treating patients with IMRT and both, IMRT and VMAT, respectively. In terms of strengths all 14 (100%) centers emphasized high energy and commitment to learning potential research collaboration, 1 (7.1%) center is a designated International Atomic Energy Agency training center and 1 (7.1%) is the only center in East Africa with Joint Commission International Accreditation. All 14 (100%) centers emphasized the need for education and training in advanced treatment planning procedures and techniques, 4 (28.6%) centers reported major gaps (including CT simulators, linear accelerator) in equipment, 5 (35.5%) minor gaps (including in-room image guidance, multi-leaf collimator) in equipment, and 5 (35.7%) gaps in physics QA devices (including film/array detectors, dose calculation software, phantoms for machine output checks). Using benchmark recommended staffing levels from Health Economics in Radiation Oncology data (HERO), 14 (100%) centers were well-staffed with physicists, 8 (57%) well-staffed with radiation oncologists and 8 (57%) well-staffed with radiation therapists.Among a motivated group of African RT centers with demonstrated interest in commissioning an IMRT program, we noted gaps in equipment for safe IMRT treatment delivery. Staffing met recommendation for physicists but not radiation oncologists and therapists. Combined survey and video interview assessment can help guide curriculum design for training programs and other areas for improvement.

MR-Linac Radiotherapy in Year One: Experience's in Imaging, Patient Treatment and Data Collection

To present our institutions initial clinical experience with a high field MR-Linac with regards to patients treated, data collected, functional imaging performed and general performance of the machine. From Aug 15, 2019 to Feb 7, 2020, thirty-three patients were treated on our 1.5 T MR-Linac with all patients enrolled in the MOMENTUM study (ClinicalTrials.gov, identifier: NCT04075305). Two types of workflows were used: one accounting for daily patient shifts only (adapt to position or ATP) and the other involving online plan adaptation through re-contouring and re-optimization based on daily MRI images (adapt to shape or ATS). Of the thirty-three patients, thirty were CNS brain patients (15 GBM and 15 other) treated using ATP and three were prostate cancer patients treated using ATS and SBRT to a dose of 40 Gy in 5 fractions. Imaging involved T1 (brain ATP) or T2 (prostate ATS) weighted scans captured online for registration/planning. Functional imaging sequences for brain ATP (DWI, MT, BOLD, CEST) were taken before, during and post irradiation in addition to T2-FLAIR. DWI was done for the prostate cases before, during and post irradiation. Timing was recorded for the various stages of the workflows. Machine performance was characterized in terms of unscheduled downtime events. A total of 540 fractions were delivered on the MR-Linac over its initial 25 weeks of use. The average session time (n = 200 fractions) for the brain ATP workflow (excluding post imaging) was 26.9 minutes (3.7 min setup, 5.5 min pre-tx imaging, 5.1 min image registration, 4.5 min plan optimization, 2.0 min physics QA, and 6.1 min beam on). The minimum session time was 24 minutes for the brain ATP. The average session time for the prostate ATS workflow (n = 10 fractions) was 47.7 minutes (6.6 min setup, 3.2 min pre-tx imaging, 3.5 min image registration, 15.1 min contouring, 5.6 min plan optimization, 1.5 min physics QA, 2.9 min verification imaging and 9.3 min beam on). Additional post beam research scans took, on average, 12.5 minutes for the prostate cases. The following multi-parametric imaging maps were generated for the brain patients: T1 and T2, ADC, T2-FLAIR, CEST asymmetry and Amide MTR. The brain T2-FLAIR signal, in some cases, reduced over the treatment course. Changes in ADC maps were observed for both brain and prostate over the treatment. In some instances, brain re-planning was done offline based on daily online T2-FLAIR imaging. In terms of downtime, patients were transferred to a standard Linac for 7.1 % of fractions due to either a magnetron change, modulator tank replacement, or a cooling issue. An MR-Linac program has been implemented at our institution involving a multi-disciplinary group with both machine data and patient data being captured. The current status, clinical and technical considerations, and most recent image-based findings will be presented.

End to end QA in image guided and adaptive radiation therapy

It has been suggested that modern radiation therapy could benefit from adopting the “End to End” (E2E) type of testing developed originally in computer science to determine whether applications and systems work as required under real-world scenarios. The motivation for adopting E2E techniques for image guided adaptive radiation therapy validation is to extend beyond current common testing using standard physics QA that inherently probes only select points or systems within the IGART schema. E2E methodologies extend the testing to evaluate complete IGART processes, including the complex interchanges that occur during and throughout a patient’s treatment as clinical staff interpret and respond to information acquired during the treatment course.While limited radiotherapy E2E QA may have been adopted periodically by clinics when implementing a new treatment technique, clinical E2E QA has been confined to date mainly to tests mediated by external auditing bodies such as IROC, the Imaging and Radiation Oncology Core in the United States. This testing often includes having the clinic in question irradiate a purpose-built phantom containing dosimeters to specific criteria under protocols set by the auditing body. The auditors then determine off site whether the clinic’s treatment process was successful by comparing the dose measurements with the intended dose delivery.The advance of three dimensional (3D) radiation dosimeters opens the possibility for in-house E2E testing. Approaches for in-house E2E testing have been proposed for over a decade, but such comprehensive internal E2E testing has not been widely adopted. In this presentation the barriers and challenges to the development of clinical in-house E2E QA will be reviewed primarily based on the experience in Kingston.

Towards Liver SBRT – A clinical experience

Historically external beam radiation therapy has not been used to treat metastatic liver and hepatocellular carcinoma (HCC), due to the increased risk of radiation induced liver disease (RILD). Remarkable advances in imaging and delivery technology can now be harnessed to enhance target localisation and local control for patients suffering with HCC and oligometastatic liver disease. Image-Guided Radiation Therapy (IGRT) and Stereotactic Body Radiation Therapy (SBRT) are rapidly revolutionising the planning and delivery of radiation therapy in the treatment of cancer. Being able to see and track the changes that take place over a radical course of radiation therapy present numerous exciting opportunities. The treatment of liver carcinoma with radiotherapy is a highly complex non-invasive treatment option that can deliver significant benefits to non-operable patients when administered successfully. Safe administration of the world’s most advanced radiotherapy treatment techniques such as 4D-IGRT or end expiration breath-hold (EEBH), flattening filter free (FFF), SBRT volumetric arc therapy (VMAT) is a highly challenging commitment and endeavour to undertake, especially so for the clinical physicist. This presentation will highlight some of the main challenges encountered when developing and implementing a liver SBRT program across a multi-disciplinary team, which includes education and training, patient selection, physics QA and establishing process-specific documentation.

O58. Illustrated instructions for training of physics QA

Introduction Physics QA procedures are typically taught one-to-one, and it can be a challenge to teach large groups of students. Furthermore, it can be difficult for students to remember details when they return to their home institution. We are investigating the use of illustrated instructions for training of physics QA. Here we report on monthly mechanical QA of medical linear accelerators. Materials and methods Illustrated instructions were created for monthly mechanical QA with tolerance tabulated, and underwent several steps of review and refinement. Testers with zero QA experience were then recruited from our radiotherapy department (1 student, 2 computational scientists and 8 dosimetrists). The following parameters were progressively de-calibrated on a Varian C-series linac: Group A = gantry angle, ceiling laser position, X1 jaw position, couch longitudinal position, physical graticule position (5 testers); Group B = Group A + wall laser position, couch lateral and vertical position, collimator angle (3 testers); Group C = Group B + couch angle, wall laser angle, and optical distance indicator (3 testers). Testers were taught how to use the linac, and then used the instructions to try to identify these errors. A physicist observed each session, giving support on machine operation, as necessary. The instructions were further tested with groups of therapists, graduate students and physics residents at multiple institutions. We have also changed the language of the instructions to simulate using the instructions with non-English speakers. Results Testers were able to follow the instructions. They determined gantry, collimator and couch angle errors within 0.4, 0.3, and 0.9 degrees of the actual changed values, respectively. Laser positions were determined within 1 mm, and jaw positions within 2 mm. Couch position errors were determined within 2 and 3 mm for lateral/longitudinal and vertical errors, respectively. Accessory positioning errors were determined within 1 mm. ODI errors were determined within 2 mm when comparing with distance sticks, and 6 mm when using blocks, indicating that distance sticks should be the preferred approach for inexperienced staff. Conclusions Inexperienced users were able to follow these instructions, and catch errors within the criteria suggested by AAPM TG142 for linacs used for IMRT.

SU‐F‐E‐17: A Dedicated Teaching and Research Linac as a Stepping Stone to Introduce Medical Physics to Students

Purpose:This work describes how a non‐clinical, research and teaching Linac is used as an extremely motivating and exciting way to introduce students to medical physics.Methods:The dedicated facility was inaugurated in 2014. The facility is composed of a fully equipped and functional state‐of‐the‐art Varian TrueBeam Linac and a complete set of physics instruments and QA phantoms for the Linac and onboard imaging. The Linac bunker and treatment console are oversized such that a class of 12–15 can comfortably fit, seated if needed for longer sessions. A 3cr undergraduate laboratory course that includes medical imaging, x‐ray source characterization (mAs, kVp, and filtering) and many others including an introductory Linac laboratory was created. The latter is composed of one general 4‐hours session and a weekly 4‐hours session for teams of two students. The general session includes a hands‐on presentation of the Linac, its environment and a formal safety and radiation protection course (with an exam).Results:Since the winter of 2015, senior undergraduate (total of 15) pursuing either the medical physics or the biomedical engineering tracks can register. At the Linac, the students are allowed full control of the experiments, including set‐up and irradiation. Supervisor intervention is limited to safety concerns for students or equipment. Measurements of output factors using two chambers (regular and small field) for various field sizes (1×1 to 30×30 cm2) and of detailed depth‐dose curves for 6 MV, 6 and 12 MeV beams are to be performed and discussed in a formal report.Conclusion:Full access to, and control of, a Linac is the high point of this course. It provides a glimpse of medical physics and generates an experimental background for those continuing to CAMPEP programs. This dedicated, non‐clinical facility further enable enhance CAMPEP graduate teaching and research activities not possible with a clinical device.

SU‐F‐T‐558: ArcCheck for Patient Specific QA in Stereotactic AblativeRadiotherapy

Purpose:Stereotactic Ablative Radiotherapy (SABR) is one of the most preferred treatment techniques for early stage lung cancer. This technique has been extended to other treatment sites like Spine, Liver, Scapula, Sternum etc., This has resulted in increased physics QA time on machine. In this study, we've tested the feasibility of using ArcCheck as an alternative method to replace film dosimetry.Methods:Twelve patients with varied diagnosis of Lung, Liver, scapula, sternum and Spine undergoing SABR were selected for this study. Pre‐treatment QA was performed for all the patients which include ionization chamber and film dosimetry. The required gamma criteria for each SABR plan to pass QA and proceed to treatment is 95% (3%,1mm). In addition to this routine process, the treatment plans were exported on to an ArcCheck phantom. The planned and measured dose from the ArcCheck device were compared using four different gamma criteria: 2%,2 mm, 3%,2 mm, 3%,1 mm and 3%, 3 mm. In addition to this, we've also introduced errors to gantry, collimator and couch angle to assess sensitivity of the ArcCheck with potential delivery errors.Results:The ArcCheck mean passing rates for all twelve cases were 76.1%±9.7% for gamma criteria 3%,1 mm, 89.5%±5.3% for 2%,2 mm, 92.6%±4.2% for 3%,2 mm, and 97.6%±2.4% for 3%,3 mm gamma criteria. When SABR spine cases are excluded, we observe ArcCheck passing rates higher than 95% for all the studied cases with 3%, 3mm, and ArcCheck results in acceptable agreement with the film gamma results.Conclusion:Our ArcCheck results at 3%, 3 mm were found to correlate well with our non‐SABR spine routine patient specific QA results (3%,1 mm). We observed significant reduction in QA time on using ArcCheck for SABR QA. This study shows that ArcCheck could replace film dosimetry for all sites except SABR spine.

SU‐E‐P‐05: Electronic Brachytherapy: A Physics Perspective On Field Implementation

Purpose:We want to summarize our experience implementing a successful program of electronic brachytherapy at several dermatology clinics with the help of a cloud based software to help us define the key program parameters and capture physics QA aspects. Optimally developed software helps the physicist in peer review and qualify the physical parameters.Methods:Using the XOFT™ Axxent™ electronic brachytherapy system in conjunction with a cloud‐based software, a process was setup to capture and record treatments. It was implemented initially at about 10 sites in California. For dosimetric purposes, the software facilitated storage of the physics parameters of surface applicators used in treatment and other source calibration parameters. In addition, the patient prescription, pathology and other setup considerations were input by radiation oncologist and the therapist. This facilitated physics planning of the treatment parameters and also independent check of the dwell time. From 2013–2014, nearly1500 such calculation were completed by a group of physicists. A total of 800 patients with multiple lesions have been treated successfully during this period. The treatment log files have been uploaded and documented in the software which facilitated physics peer review of treatments per the standards in place by AAPM and ACR.Results:The program model was implemented successfully at multiple sites. The cloud based software allowed for proper peer review and compliance of the program at 10 clinical sites. Dosimtery was done on 800 patients and executed in a timely fashion to suit the clinical needs. Accumulated physics data in the software from the clinics allows for robust analysis and future development.Conclusion:Electronic brachytherapy implementation experience from a quality assurance perspective was greatly enhanced by using a cloud based software. The comprehensive database will pave the way for future developments to yield superior physics outcomes.

MO‐A‐16A‐01: QA Procedures and Metrics: In Search of QA Usability

Radiation therapy has undergone considerable changes in the past two decades with a surge of new technology and treatment delivery methods. The complexity of radiation therapy treatments has increased and there has been increased awareness and publicity about the associated risks. In response, there has been proliferation of guidelines for medical physicists to adopt to ensure that treatments are delivered safely. Task Group recommendations are copious, and clinical physicists' hours are longer, stretched to various degrees between site planning and management, IT support, physics QA, and treatment planning responsibilities.Radiation oncology has many quality control practices in place to ensure the delivery of high‐quality, safe treatments. Incident reporting systems have been developed to collect statistics about near miss events at many radiation oncology centers. However, tools are lacking to assess the impact of these various control measures. A recent effort to address this shortcoming is the work of Ford et al (2012) who recently published a methodology enumerating quality control quantification for measuring the effectiveness of safety barriers. Over 4000 near‐miss incidents reported from 2 academic radiation oncology clinics were analyzed using quality control quantification, and a profile of the most effective quality control measures (metrics) was identified. There is a critical need to identify a QA metric to help the busy clinical physicists to focus their limited time and resources most effectively in order to minimize or eliminate errors in the radiation treatment delivery processes. In this symposium the usefulness of workflows and QA metrics to assure safe and high quality patient care will be explored. Two presentations will be given:Quality Metrics and Risk Management with High Risk Radiation Oncology ProceduresStrategies and metrics for quality management in the TG‐100 EraLearning Objectives: Provide an overview and the need for QA usability metrics: Different cultures/practices affecting the effectiveness of methods & metrics. Show examples of quality assurance workflows, Statistical process control, that monitor the treatment planning and delivery process to identify errors. To learn to identify and prioritize risks and QA procedures in radiation oncology. Try to answer the question: Can a quality assurance program aided by quality assurance metrics help minimize errors and ensure safe treatment delivery. Should such metrics be institution specific.

Radiation Doses and Risks Associated with Mammographic Screening

Radiation dose and the associated risk to the breast are being studied in much detail with the aim of justifying breast cancer screening. The mean glandular dose has been proposed as the proper quantity to describe risks incurred by radiation. X. Wu (US) and D. Dance (UK) were the first authors to standardize breast dosimetry and their conversion tables have been used throughout. Doses can be calculated for specific population samples or for individual patients, in which case an accurate estimate of the glandular tissue fraction should be known. From specific DICOM tags in the digital images and access to tube output measurements from the medical physics QA, patient dose assessment can be largely automated. Other (traditional) approaches mimic clinical exposures on a Perspex phantom and use these exposures to estimate the breast dose to a typical breast. Any local data, both patient dose data and doses to Perspex, can these days be compared to an extensive amount of published dose values. Radiation dose and image quality should both be considered in screening applications. Better image quality can have a significant effect on diagnostic performance. As only a small increase in performance (ex. detected fraction) gained can mean an enormous amount of women saved, image quality settings should be optimized and not minimized. Risk benefit investigation should therefore focus on performance rather than dose. For a few screening programs, the benefits could be proven. Emerging technologies should be investigated along the same basic principles.

SU-E-T-198: Patient Scheduling Monitor (PSM)-A New Tool for Radiation Therapy Patient Scheduling and Workflow Management in an Increasingly Digital Environment.

To develop an easy-to-use and customizable Patient Scheduling Monitor for 1) active monitoring of radiation therapy workflow from CT simulation to the start of treatment and 2) for optimizing the workflow based on treatment complexity. Microsoft Access database and Visual Basic language were used to create an in-house software application, Patient Scheduling Monitor (PSM). The PSM was designed with three functional modules: a patient schedule calculator, a workflow progress tracker, and a workflow evaluator. The PSM divides the radiation treatment workflow into 6 tasks including image acquisition/fusion, target delineation, dosimetry planning, MD review, physics QA and RTT QA. On the day of CT simulation, the scheduling calculator generates a planned timeline for each task based on the CT-simulation date and the default standard established for each given task and treatment type. Each task within the PSM can also be individualized as needed. After simulation, the progress tracker enables staff to actively monitor the workflow. The workflow evaluator will query the database and analyze the planned versus actual timeline and provide data for future workflow analysis. We have used the PSM since Nov, 2011 for 186 patients. The PSM has allowed us to provide patient start times at the completion of simulation. It has helped to improve patient satisfaction. The workflow progress tracker enabled us to actively manage the workflow. Currently, for patients managed using the PSM, no rescheduling has been required. The use of PSM has reduced the average CT simulation to treatment start times. It also has improved intradepartmental communications. An easy-to-use patient scheduling monitor has been developed. The PSM has been shown to be an efficient and effective tool in managing, assessing and improving the radiation therapy workflow and will be useful in managing the timelines in an increasingly dynamic working environment.

SU-E-T-57: Comprehensive Web-Based QA in Radiation Oncology

Purpose: To describe a framework for comprehensive web‐based QA in medical physics and radiation oncology through centralized access to multiple databases. We believe that this form of centralized QA represents the future direction for data analysis and visualization in increasingly data‐driven radiation oncology and medical physics practises. Methods and Materials: Our paperless radiation oncology clinic, equipped with a centralized webserver running PERL scripts for access to the Varian ARIA record‐and‐verify database and a custom MySQL database for medical physics QA data, adverse event reports and in‐house clinical trial data. Results: Our planned framework for comprehensive electronic QA is outlined and some early results showing the power of the system for analysingtreatment times and for statistical process control are presented. Conclusions: Comprehensive web‐based QA represents the future direction for data archiving and visualization in the medical physics and radiation oncology community. We present our framework for web‐based QA and demonstrate its power with some early results.

WE-A-BRB-01: Single and Hypo-Fractionated Stereotactic Irradiation of Brain & Body Lesions

Stereotactic irradiation has been in clinical use for decades. It was initially performed almost exclusively for brain lesions with Gamma Knife radiosurgery. In the 1990s, it was expanded to the rest of the body. Over the years the emphasis has shifted from benign lesions like AVMs to malignancies such as early‐stage lungcarcinoma in medically inoperable patients. Stereotactic body radiation therapy(SBRT) now is available at approximately 700 institutions in the United States (American Hospital Association guide 2009). Almost 1500 articles have been published on SBRT, and there are several ongoing prospective randomized trials comparing SBRT with standard radiation therapy. Major considerations in single and hypo‐fractionated radiotherapy are the therapeutic gain and technical challenges for precise imaging, planning, and dose delivery. In this educational session, we will first briefly review the results of recently completed studies for intracranial and extracranial stereotactic irradiation with an emphasis on SBRT; and then discuss the technical aspects in image registration, stereotactic localization, target delineation uncertainties particularly using FDG‐PET for the lungcancer; and finally address the physics QA procedures to ensure optimal planning that differentiate the doses between tumor and normal tissue without detracting of target coverage and to deliver the desired dose under image‐guidance using stereotactic frame or frameless refixation systems. Learning Objectives: 1. Understand the therapeutic gain in stereotactic radiosurgery(SRS) or hypo‐fractionated SBRT and recognize that the success of SBRT relies on both the dose escalation to the tumor and the margin reduction and tumor shrinkage 2. Discuss the rationale and technical details about how to use fine CT or MRI scans for the delineation of small targets and critical structures, how to eliminate motion or other image artifacts using stereotactic‐type image localization, and how to combine anatomic information from CT or MRI with physiological information from PET or functional MRI for optimal treatment planning 3. Learn the physics QA procedures for plan evaluation with empirical rules on the conformity index, target coverage, and periphery dose gradient, and QA for dose delivery under image‐guided target refixation and patient tracking 4. Develop mock training for SBRT in procedural design and implementation for annual training of the SBRT team to prevent the occurrence of systematic and human errors

SU-GG-T-54: A Phantom for Physics QA to Check the Accuracy of an Ir-192 Stepping Source Dwell Position and Reproducibility of Dwell Time in HDR Brachytherapy

Purpose: To determine the accuracy of dwell position, reproducibility of dwell time and effect of bending a transfer tube for Ir‐192 high‐dose rate (HDR) brachytherapy stepping source using an in‐house made phantom. Method and Materials: Experiments were performed using a Nucletron microselectron V3 (30) HDR after loading device with Ir‐192 single stepping source, Fuji Capusla XL computed radiography(CR) cassette and its reader and an in‐house made phantom. The central part of the phantom, which has alternating strips of lead and Perspex was used to check the accuracy of dwell positions while the outer part of the phantom, which consists of four different materials, namely perspex, copper,aluminium and Styro‐foam, was used to measure reproducibility of dwell time. Images were exported via network as DICOM images for further analysis by ImageJ.Results: Positional error of an HDR source smaller than 1.0 mm can be detected. Hence, it is possible to regularly check dwell positions for selected transfer tubes of a treatment plan as a quick verification of dwell positions. Reproducibility of dwell time within 0.1 second could be verified. No effect of bending a transfer tube was observed for normal clinical situations. However, under extreme cases in which the transfer tube was highly bent, the source dwell position was changed by less than 0.5mm. Conclusion: The phantom was capable of detecting dwell positional error of 1.0 mm and reproducibility of dwell time of 0.1 second. For typical clinical scenarios in which transfer tubes are bent, no effect on dwell position was observed. The phantom can be used with radiographic films or CR cassette with the latter being a preferred tool, as hospitals are phasing out film processors in favour of digital technology. The method is simple and robust for routine use.

SU‐GG‐T‐297: DMLC Leaf Position Tests for Dynamic Arc Using Array Detector Devices

Purpose: For dynamic arc and intensity modulated arc therapies, new challenges have arisen in treatment commissioning and routine physics QA due to additional variation in gantry rotation. A specific dMLC test for leaf position accuracy in dynamic arc deliveries using commercial available 2D array devices was tried. Materials and Methods: The method of the dMLC dynamic test was developed based on a Picket Fence type test which was originally designed for static gantry application. The new tests were performed either at a series of fixed gantry angles in the range of 360 degree or dynamically with a rotating gantry and a dynamical MLC delivery. A PTW Seven29 ion chamber array and a Sun Nuclear MapCheck diode array were employed as detection devices for the measurements. Results: The results measured from both devices showed similar intensity distributions in dynamic Picked Fence patterns. The results were also consistent with our previous film dosimetry studies, which implicates that the leaf position accuracy could be degraded due to gantry dynamical rotation. The difference from the results of two different device measurements were compared with each other, and the pro and con for the measurements using these two devices were discussed. Conclusion: Our tests could detect MLC leaf displacements at specific gantry angles and due to gantry rotation. The test could be implemented for a routine MLC QA for those dynamic arc therapies such as dynamic conformal arc and volumetric modulated arc therapies. While both PTW and Sun Nuclear array detectors could be easily used for a routine arc QA procedure, the PTW Seven29 ion chamber array provides a better resolution and much lesser dependence on the mechanical setup accuracy. Conflict of Interest: Peer Koltermann is an employee of PTW

Sci-Wed PM: Delivery-03: Commissioning of DAVID -”Device for Advanced Verification of IMRT Deliveries”

The ”Device for Advanced Verification of IMRT Deliveries” — DAVID is a transparent, segmented, multi-wire ionization chamber. It attaches to the accessory holder of the gantry. Each wire is centered to the field defined by a leaf pair. The integrated signal measured in each wire is related to the dose delivered to the patient by the modulated incident beam. Thus, at this time DAVID is the only device able to measure an undisturbed signal, related only to Linac parameters. The software compares the signals measured during the radiotherapy session to a reference acquired during the pre-treatment QA process. DAVID is intended for documenting the radiation delivery constancy of conformal plans, IMRT (Step & Shoot and Sliding window) and RapidArc techniques in real time, during patient treatment. Though not originally intended, DAVID has the potential to perform a number of Linac Physics QA tests. DAVID is a new product in North America. Currently only two are in use, one in New York and the other in Abbotsford, Canada. In order to employ effectively DAVID for routine clinical use, we performed a comprehensive set of measurements. The list includes transmission factors, signal reproducibility with field size and gantry angle, daily setup error of the device, field edge position sensitivity, dose rate signal dependence, EDW constancy, dosimetric leaf gap, picket fence and preliminary work on IMRT verification. All measured data was processed by statistical methods. Our results show that the DAVID system is an effective tool for monitoring IMRT delivery consistency.

SU-FF-T-221: Efficient Registration of Dose Distributions

Purpose: To develop efficient algorithms to compute the optimal alignment between two high resolution 2D dose distributions (usually one calculated, one measured), with one of them as a reference. This will help eliminate 2D dosimeter setup errors and/or misalignments between radiation and light fields, which both affect the integrity of the IMRT‐QA process. We feel that these algorithms will also serve as a useful tool for other physics QA procedures involving calculation/measurement of planar dose/fields. Method and Materials: The mathematical objective of alignment is to maximize the percentage of points that pass a similarity test. Two commonly used similarity tests, viz., the composite test (DTA/dose difference) and the gamma test are considered. The algorithms work by efficiently and exhaustively examining a search space of alignments that are in a predefined neighborhood (say, 10 mm in each direction) of the initial alignment, for translational transformations that maximize the objective. The resulting alignments are guaranteed to be optimal provided that the optimal solution lies within that neighborhood. Mathematical properties of the objective function are utilized for efficient algorithm design. The program execution time depends on the selection of size of the neighborhood to be searched, which may be reduced by visually or automatically (using image registration) picking a good starting alignment. Results: For registering two 140*140 distributions with 1 mm spatial resolution and with the 5%/5 mm gamma criterion, the algorithm executes within a few seconds for a search within 10 mm of the initial alignment on a 1.7 GHz processor. Conclusion: We present efficient and optimal algorithms to determine the best alignment of two 2D dose distributions for IMRT‐QA. New or enhanced algorithms are needed to correct rotational misalignments and to extend the work to 3D dose distributions that may be measured using 3D diode arrays or gel dosimeters.