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DOE OSTI2013

Dynamic rotating-shield brachytherapy

Purpose: To present dynamic rotating shield brachytherapy (D-RSBT), a novel form of high-dose-rate brachytherapy (HDR-BT) with electronic brachytherapy source, where the radiation shield is capable of changing emission angles during the radiation delivery process.Methods: A D-RSBT system uses two layers of independently rotating tungsten alloy shields, each with a 180° azimuthal emission angle. The D-RSBT planning is separated into two stages: anchor plan optimization and optimal sequencing. In the anchor plan optimization, anchor plans are generated by maximizing the D{sub 90} for the high-risk clinical-tumor-volume (HR-CTV) assuming a fixed azimuthal emission angle of 11.25°. In the optimal sequencing, treatment plans that most closely approximate the anchor plans under the delivery-time constraint will be efficiently computed. Treatment plans for five cervical cancer patients were generated for D-RSBT, single-shield RSBT (S-RSBT), and {sup 192}Ir-based intracavitary brachytherapy with supplementary interstitial brachytherapy (IS + ICBT) assuming five treatment fractions. External beam radiotherapy doses of 45 Gy in 25 fractions of 1.8 Gy each were accounted for. The high-risk clinical target volume (HR-CTV) doses were escalated such that the D{sub 2cc} of the rectum, sigmoid colon, or bladder reached its tolerance equivalent dose in 2 Gy fractions (EQD2 with α/β= 3 Gy) of 75 Gy, 75 Gy, or 90 Gy, respectively.Results: For the patients considered, IS + ICBT had an average total dwell time of 5.7 minutes/fraction (min/fx) assuming a 10 Ci{sup 192}Ir source, and the average HR-CTV D{sub 90} was 78.9 Gy. In order to match the HR-CTV D{sub 90} of IS + ICBT, D-RSBT required an average of 10.1 min/fx more delivery time, and S-RSBT required 6.7 min/fx more. If an additional 20 min/fx of delivery time is allowed beyond that of the IS + ICBT case, D-RSBT and S-RSBT increased the HR-CTV D{sub 90} above IS + ICBT by an average of 16.3 Gy and 9.1 Gy, respectively.Conclusions: For cervical cancer patients, D-RSBT can boost HR-CTV D{sub 90} over IS + ICBT and S-RSBT without violating the tolerance doses to the bladder, rectum, or sigmoid. The D{sub 90} improvements from D-RSBT depend on the patient, the delivery time budget, and the applicator structure.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2014

SU-E-T-133: Dosimetric Impact of Scan Orientation Relative to Target Motion During Spot Scanning Proton Therapy

Purpose: This study seeks to evaluate the dosimetric effects of intra-fraction motion during spot scanning proton beam therapy as a function of beam-scan orientation and target motion amplitude. Method: Multiple 4DCT scans were collected of a dynamic anthropomorphic phantom mimicking respiration amplitudes of 0 (static), 0.5, 1.0, and 1.5 cm. A spot-scanning treatment plan was developed on the maximum intensity projection image set, using an inverse-planning approach. Dynamic phantom motion was continuous throughout treatment plan delivery.The target nodule was designed to accommodate film and thermoluminescent dosimeters (TLD). Film and TLDs were uniquely labeled by location within the target. The phantom was localized on the treatment table using the clinically available orthogonal kV on-board imaging device. Film inserts provided data for dose uniformity; TLDs provided a 3% precision estimate of absolute dose. An inhouse script was developed to modify the delivery order of the beam spots, to orient the scanning direction parallel or perpendicular to target motion.TLD detector characterization and analysis was performed by the Imaging and Radiation Oncology Core group (IROC)-Houston. Film inserts, exhibiting a spatial resolution of 1mm, were analyzed to determine dose homogeneity within the radiation target. Results: Parallel scanning and target motions exhibited reduced target dose heterogeneity, relative to perpendicular scanning orientation. The average percent deviation in absolute dose for the motion deliveries relative to the static delivery was 4.9±1.1% for parallel scanning, and 11.7±3.5% (p<<0.05) for perpendicularly oriented scanning. Individual delivery dose deviations were not necessarily correlated to amplitude of motion for either scan orientation. Conclusions: Results demonstrate a quantifiable difference in dose heterogeneity as a function of scan orientation, more so than target amplitude. Comparison to the analyzed planar dose of a single field hint that multiple-field delivery alters intra-fraction beam-target motion synchronization and may mitigate heterogeneity, though further study is warranted.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

SU-E-T-136: Dosimetric Robustness of a Magnetic Resonance Imaging Guided Radiation Therapy (MR-IGRT) System

Purpose: To test the radiation delivery robustness of the first MR-IGRT system using a commercial cylindrical diode array detector (ArcCHECK) and an ionization thimble chamber (Exradin A18). Methods: The MR-IGRT system is composed of three evenly spaced Co-60 sources on a rotating gantry located between two magnet halves. The collimator for each source consists of 30 doubly-focused leaf pairs that allow the system to deliver both conformal and intensity modulated (IMRT) treatment plans. The system's delivery robustness was tested over a span of 6 months from September 2013 through February 2014. This was achieved by repeatedly delivering 10 patient plans. These plans consisted of 2 conformal prostates, 2 IMRT prostates, 2 IMRT head and neck, 2 IMRT breast, 1 IMRT pancreas, and 1 IMRT bladder. The plans were generated with the system's treatment planning software. Once the plans were generated, quality assurance plans were created on a digital ArcCHECK dataset. The ArcCHECK used for testing was specially designed to be MR-compatible by moving the power supply outside of the magnetic field. The A18 ionization chamber was placed in a custom plastic plug insert in the center of the ArcCHECK. Gamma analysis was used with the ArcCHECK for relative dose evaluating both 3%/3mm and 2%/2mm. Absolute point dose was compared between ion chamber measurement and treatment plan. Results: The ArcCHECK passing rate remained constant over the 6 month period. The average passing rate for 3%/3mm and 2%/2mm analysis was 98.6% ± 0.7 and 88.8% ± 2.9, respectively. The ion chamber measurements showed little variation with an average percent difference between planned dose verses measured dose of 0.9% ± 0.7. Conclusion: Minimal differences were noted in the delivery of the 10 patient plans. Over a period that included acceptance testing, commissioning, and clinical deliveries, the MR-IGRT system remained consistent in radiation delivery.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

SU-E-T-192: FMEA Severity Scores - Do We Really Know?

Purpose: Failure modes and effects analysis (FMEA) is a subjective risk mitigation technique that has not been applied to physics-specific quality management practices. There is a need for quantitative FMEA data as called for in the literature. This work focuses specifically on quantifying FMEA severity scores for physics components of IMRT delivery and comparing to subjective scores. Methods: Eleven physical failure modes (FMs) for head and neck IMRT dose calculation and delivery are examined near commonly accepted tolerance criteria levels. Phantom treatment planning studies and dosimetry measurements (requiring decommissioning in several cases) are performed to determine the magnitude of dose delivery errors for the FMs (i.e., severity of the FM). Resultant quantitative severity scores are compared to FMEA scores obtained through an international survey and focus group studies. Results: Physical measurements for six FMs have resulted in significant PTV dose errors up to 4.3% as well as close to 1 mm significant distance-to-agreement error between PTV and OAR. Of the 129 survey responses, the vast majority of the responders used Varian machines with Pinnacle and Eclipse planning systems. The average years of experience was 17, yet familiarity with FMEA less than expected. Survey reports perception of dose delivery error magnitude varies widely, in some cases 50% difference in dose delivery error expected amongst respondents. Substantial variance is also seen for all FMs in occurrence, detectability, and severity scores assigned with average variance values of 5.5, 4.6, and 2.2, respectively. Survey shows for MLC positional FM(2mm) average of 7.6% dose error expected (range 0–50%) compared to 2% error seen in measurement. Analysis of ranking in survey, treatment planning studies, and quantitative value comparison will be presented. Conclusion: Resultant quantitative severity scores will expand the utility of FMEA for radiotherapy and verify accuracy of FMEA results compared to highly variable subjective scores.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

SU-E-T-453: A Novel Daily QA System for Robotic Image Guided Radiosurgery with Variable Aperture Collimator

Purpose: A novel end-to-end system using a CCD camera and a scintillator based phantom that is capable of measuring the beam-by-beam delivery accuracy of Robotic Radiosurgery has been developed and reported in our previous work. This work investigates its application to end-to-end type daily QA for Robotic Radiosurgery (Cyberknife) with Variable Aperture Collimator (Iris). Methods: The phantom was first scanned with a CT scanner at 0.625 slice thickness and exported to the Cyberknife Muliplan (v4.6) treatment planning system. An isocentric treatment plan was created consisting of ten beams of 25 Monitor Units each using Iris apertures of 7.5, 10, 15, 20, and 25 mm. The plan was delivered six times in two days on the Cyberknife G4 system with fiducial tracking on the four metal fiducials embedded in phantom with re-positioning between the measurements. The beam vectors (X, Y, Z) are measured and compared with the plan from the machine delivery file (XML file). The Iris apertures (FWHM) were measured from the beam flux map and compared with the commissioning data. Results: The average beam positioning accuracies of the six deliveries are 0.71 ± 0.40 mm, 0.72 ± 0.44 mm, 0.74 ± 0.42 mm, 0.70 ± 0.40 mm, 0.79 ± 0.44 mm and 0.69 ± 0.41 mm respectively. Radiation beam width (FWHM) variations are within ±0.05 mm, and they agree with the commissioning data within 0.22 mm. The delivery time for the plan is about 7 minutes and the results are given instantly. Conclusion: The experimental results agree with stated sub-millimeter delivery accuracy of Cyberknife system. Beam FWHM variations comply with the 0.2 mm accuracy of the Iris collimator at SAD. The XRV-100 system has proven to be a powerful tool in performing end-to-end type tests for Robotic Image Guided Radiosurgery Daily QA.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2014

SU-E-T-613: Dosimetric Consequences of Systematic MLC Leaf Positioning Errors

Purpose: The purpose of this study is to determine the dosimetric consequences of systematic MLC leaf positioning errors for clinical IMRT patient plans so as to establish detection tolerances for quality assurance programs. Materials and Methods: Dosimetric consequences were simulated by extracting mlc delivery instructions from the TPS, altering the file by the specified error, reloading the delivery instructions into the TPS, recomputing dose, and extracting dose-volume metrics for one head-andneck and one prostate patient. Machine error was simulated by offsetting MLC leaves in Pinnacle in a systematic way. Three different algorithms were followed for these systematic offsets, and are as follows: a systematic sequential one-leaf offset (one leaf offset in one segment per beam), a systematic uniform one-leaf offset (same one leaf offset per segment per beam) and a systematic offset of a given number of leaves picked uniformly at random from a given number of segments (5 out of 10 total). Dose to the PTV and normal tissue was simulated. Results: A systematic 5 mm offset of 1 leaf for all delivery segments of all beams resulted in a maximum PTV D98 deviation of 1%. Results showed very low dose error in all reasonably possible machine configurations, rare or otherwise, which could be simulated. Very low error in dose to PTV and OARs was shown in all possible cases of one leaf per beam per segment being offset (<1%), or that of only one leaf per beam being offset (<.2%). The errors resulting from a high number of adjacent leaves (maximum of 5 out of 60 total leaf-pairs) being simultaneously offset in many (5) of the control points (total 10–18 in all beams) per beam, in both the PTV and the OARs analyzed, were similarly low (<2–3%). Conclusions: The above results show that patient shifts and anatomical changes are the main source of errors in dose delivered, not machine delivery. These two sources of error are “visually complementary” and uncorrelated (albeit not additive in the final error) and one can easily incorporate error resulting from machine delivery in an error model based purely on tumor motion.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

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 Era Learning Objectives: Provide an overview and the need for QA usability metrics: Different cultures/practices affecting the effectiveness of methods and 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.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2014

MO-C-BRF-01: Pediatric Treatment Planning I: Overview of Planning Strategies

Most Medical Physicists working in radiotherapy departments see few pediatric patients. This is because, fortunately, children get cancer at a rate nearly 100 times lower than adults. Children have not smoked, abused alcohol, or been exposed to environmental carcinogens for decades, and of course, have not fallen victim to the aging process. Children get very different cancers than adults. Breast or prostate cancers, typical in adults, are rarely seen in children but instead a variety of tumors occur in children that are rarely seen in adults; examples are germinomas, ependymomas and primitive neuroectodermal tumors, which require treatment of the child's brain or neuroblastoma, requiring treatment in the abdomen. The treatment of children with cancer using radiation therapy is one of the most challenging planning and delivery problems facing the physicist. This is because bones, brain, breast tissue, and other organs are more sensitive to radiation in children than in adults. Because most therapy departments treat mostly adults, when the rare 8 year-old patient comes to the department for treatment, the physicist may not understand the clinical issues of his disease which drive the planning and delivery decisions. Additionally, children are more prone than adults to developing secondary cancers after radiation. This fact has important implications for the choice of delivery techniques, especially when considering IMRT. For bilateral retinoblastoma for example, an irradiated child has a 50% chance of developing a second cancer by age 50. In the first presentation, an overview of childhood cancers and their corresponding treatment techniques will be given. These can be some of the most complex treatments that are delivered in the radiation therapy department. These cancers include leukemia treated with total body irradiation, medulloblastoma, treated with craniospinal irradiation plus a conformal boost to the posterior fossa, neuroblastoma, requiring focal abdominal irradiation to avoid kidney, liver, and vertebral body damage, retinoblastoma, requiring treatment to an eye while minimizing dose to surrounding tissues, and a variety of other tumors which occur anywhere in the body. Case studies will be presented showing the treatment technique and resulting dosimetry, highlighting the objectives for tumor coverage and organ-at-risk sparing. Practical issues that have to be faced when treating children will also be discussed such as daily sedation and immobilization. In the second presentation, specific focus will be on radiation therapy simulation, treatment planning guidelines, image guidance for delivery, and proton therapy for children. We will discuss uniqueness of pediatric simulation with different imaging modalities (CT, MRI, and PET). Some related issues are sedation for younger patients, radiation exposure reduction for CT, distortion and artifacts on pediatric MRI, and measuring pediatric organ motion. We will discuss the tradeoff of tumor coverage and normal tissue sparing in treatment planning using example organ data. Image guidance approaches for pediatric radiation therapy and methods for dose reduction will be reviewed. Finally, we will describe technical advances and trends in proton therapy for children. Advantages, caveats, and opportunities will be presented. Learning Objectives: Improve understanding about childhood cancer and treatment with radiation Understand treatment planning and delivery issues specific to children Become aware of specific treatment methods for the most challenging pediatric cancers Know the current status of state-of-the-art treatment techniques for pediatric radiation therapy.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

WE-A-19A-01: SRT I: Comparison of SRT Techniques

Within the past several years, the field of radiosurgery has seen numerous technological enhancements, including new dedicated devices for stereotactic delivery, the use of re-locatable frames to facilitate fractionated delivery and the image guided frameless approaches. The goal of this symposium is to compare and contrast competing technologies for cranial SRS/SRT. The symposium will open with a review of the general concept of cranial SRS/SRT procedures as well as describe the key differences from conventional radiotherapy. The speakers will then review each of the delivery technique (Gamma Knife, CyberKnife and Conventional linear accelerator) in turn. The focus of each speaker will be to describe the general workflow of each SRS modality, indications and counterindications for treatment. To compare and contrast different technologies, 2–3 cases examples demonstrating interesting treatment situations and expected outcomes, a sample treatment plan (either live or pre-recorded with live commentary) demonstrating the treatment planning technique, and machine and patient-specific QA required for treatment (if applicable). Additionally, workflows and data describing the use of immobilization devices or tracking/monitoring during SRS/SRT delivery will also be discussed. The session will close with a roundtable discussion of methods to evaluate plan quality, and achievable technical and clinical goals for intracranial SRS. Learning Objectives: Understand the key differences between cranial SRS/SRT and conventional treatments. Review Gamma Knife, CyberKnife and Conventional Linac-based radiosurgery delivery techniques and quality assurance Compare and contrast treatment plans, treatment planning strategy and and quality assurance procedures for each technology. Be able to establish cranial SRS/SRT procedure with optimized quality assurance program for each technology.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

WE-E-BRE-04: Dual Focal Spot Dose Painting for Precision Preclinical Radiobiological Investigations

Purpose: Recent progress in small animal radiotherapy systems has provided the foundation for delivering the heterogeneous, millimeter scale dose distributions demanded by preclinical radiobiology investigations. Despite advances in preclinical dose planning, delivery of highly heterogeneous dose distributions is constrained by the fixed collimation systems and large x-ray focal spot common in small animal radiotherapy systems. This work proposes a dual focal spot dose optimization and delivery method with a large x-ray focal spot used to deliver homogeneous dose regions and a small focal spot to paint spatially heterogeneous dose regions. Methods: Two-dimensional dose kernels were measured for a 1 mm circular collimator with radiochromic film at 10 mm depth in a solid water phantom for the small and large x-ray focal spots on a recently developed small animal microirradiator. These kernels were used in an optimization framework which segmented a desired dose distribution into low- and high-spatial frequency regions for delivery by the large and small focal spot, respectively. For each region, the method determined an optimal set of stage positions and beam-on times. The method was demonstrated by optimizing a bullseye pattern consisting of 0.75 mm radius circular target and 0.5 and 1.0 mm wide rings alternating between 0 and 2 Gy. Results: Compared to a large focal spot technique, the dual focal spot technique improved the optimized dose distribution: 69.2% of the optimized dose was within 0.5 Gy of the intended dose for the large focal spot, compared to 80.6% for the dual focal spot method. The dual focal spot design required 14.0 minutes of optimization, and will require 178.3 minutes for automated delivery. Conclusion: The dual focal spot optimization and delivery framework is a novel option for delivering conformal and heterogeneous dose distributions at the preclinical level and provides a new experimental option for unique radiobiological investigations. Funding Support: this work is supported by funding the National Sciences and Engineering Research Council of Canada, and a Mitacs-accelerate fellowship. Conflict of Interest: Dr. Lindsay and Dr. Jaffray are listed as inventors of the small animal microirradiator described herein. This system has been licensed for commercial development.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

TH-C-12A-12: Veritas: An Open Source Tool to Facilitate User Interaction with TrueBeam Developer Mode

Purpose: To address the challenges of creating delivery trajectories and imaging sequences with TrueBeam Developer Mode, a new open-source graphical XML builder, Veritas, has been developed, tested and made freely available. Veritas eliminates most of the need to understand the underlying schema and write XML scripts, by providing a graphical menu for each control point specifying the state of 30 mechanical/dose axes. All capabilities of Developer Mode are accessible in Veritas. Methods: Veritas was designed using QT Designer, a ‘what-you-is-what-you-get’ (WYSIWIG) tool for building graphical user interfaces (GUI). Different components of the GUI are integrated using QT's signals and slots mechanism. Functionalities are added using PySide, an open source, cross platform Python binding for the QT framework. The XML code generated is immediately visible, making it an interactive learning tool. A user starts from an anonymized DICOM file or XML example and introduces delivery modifications, or begins their experiment from scratch, then uses the GUI to modify control points as desired. The software automatically generates XML plans following the appropriate schema. Results: Veritas was tested by generating and delivering two XML plans at Brigham and Women's Hospital. The first example was created to irradiate the letter ‘B’ with a narrow MV beam using dynamic couch movements. The second was created to acquire 4D CBCT projections for four minutes. The delivery of the letter ‘B’ was observed using a 2D array of ionization chambers. Both deliveries were generated quickly in Veritas by non-expert Developer Mode users. Conclusion: We introduced a new open source tool Veritas for generating XML plans (delivery trajectories and imaging sequences). Veritas makes Developer Mode more accessible by reducing the learning curve for quick translation of research ideas into XML plans. Veritas is an open source initiative, creating the possibility for future developments and collaboration with other researchers. I am an employee of Varian Medical Systems.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2014

SU-C-16A-01: In Vivo Source Position Verification in High Dose Rate (HDR) Prostate Brachytherapy Using a Flat Panel Imager: Initial Clinical Experience

Purpose: We report our initial clinical experience with a novel position-sensitive source-tracking system based on a flat panel imager. The system has been trialled with 4 prostate HDR brachytherapy patients (8 treatment fractions) in this initial study. Methods: The flat panel imaging system was mounted under a customised carbon fibre couch top assembly (Figure 1). Three gold fiducial markers were implanted into the prostate of each patient at the time of catheter placement. X-ray dwell position markers were inserted into three catheters and a radiograph acquired to locate the implant relative to the imaging device. During treatment, as the HDR source dwells were delivered, images were acquired and processed to determine the position of the source in the patient. Source positions measured by the imaging device were compared to the treatment plan for verification of treatment delivery. Results: Measured dwell positions provided verification of relative dwell spacing within and between catheters, in the coronal plane. Measurements were typically within 2.0mm (0.2mm – 3.3mm, s.d. 0.8mm) of the planned positions over 60 dwells (Figure 2). Discrimination between larger dwell intervals and catheter differentiation were clear. This confirms important delivery attributes such as correct transfer tube connection, source step size, relative catheter positions and therefore overall correct plan selection and delivery. The fiducial markers, visible on the radiograph, provided verification of treatment delivery to the correct anatomical location. The absolute position of the dwells was determined by comparing the measured dwell positions with the x-ray markers from the radiograph, validating the programmed treatment indexer length. The total impact on procedure time was less than 5 minutes. Conclusion: The novel, noninvasive HDR brachytherapy treatment verification system was used clinically with minor impact on workflow. The system allows verification of correct treatment delivery, free of most potential human related errors identified in ICRP 97. This research is supported by funding from the Australian Government Department of Health through Cancer Australia grant no. 616614.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

SU-E-J-194: Continuous Patient Surface Monitoring and Motion Analysis During Lung SBRT

Purpose: Continuous monitoring of the SBRT lung patient motion during delivery is critical for ensuring adequate target volume margins in stereotactic body radiotherapy (SBRT). This work assesses the deviation of the patient surface motion using a real-time surface tracking system throughout treatment delivery. Methods: Our SBRT protocol employs abdominal compression to reduce the diaphragm movement to within 1 cm, and this is confirmed daily with fluoroscopy. Most patients are prescribed 3–5 fractions, and on treatment day a repeat motion analysis with fluoroscopy is performed, followed by a kV CBCT is aligned with the original planning CT image for 3D setup confirmation. During this entire process a patient surface data restricted to whole chest or the sternum at the middle of the breathing cycle was captured using AlignRT optical surface tracking system and defined as a reference surface. For 10 patients, the deviation of the patient position from the reference surface was recorded during the SBRT delivery in the anterior-posterior (AP) direction at 3–6 measurements per second. Results: On average, the patient position deviated from the reference surface more than 4 mm, 3 mm and 2 mm in the AP direction for 0.95%, 3.7% and 11.1% of the total treatment time, respectively. Only one of the 10 patients showed that the maximum deviation of the patient surface during the SBRT delivery was greater than 1 cm. The average deviation of the patient surface from the reference surface during the SBRT delivery was not greater than 1.6 mm for any patient. Conclusion: This investigation indicates that AP motion can be significant even though the frequency is low. Continuous monitoring during SBRT has demonstrated value in monitoring patient motion ensuring that margins selected for SBRT are appropriate, and the use of non-ionizing and high-frequency imaging can provide useful indicators of motion during treatment.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

SU-E-T-426: Feasibility of Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancer Using Volumetric Modulated Arc Therapy (VMAT) with Active Breathing Control (ABC)

Purpose: SBRT shows excellent tumor control and toxicity rates for patients with locally advanced pancreatic cancer (PCA). Herein, we evaluate the feasibility of using VMAT with ABC for PCA SBRT. Methods: Nine PCA patients previously treated via SBRT utilizing 11-beam step-and-shoot IMRT technique in our center were retrospectively identified, among whom eight patients received 3300cGy in 5 fractions while one received 3000cGy in 5 fractions. A VMAT plan was generated on each patient’s planning CT in Pinnacle v9.8 on Elekta Synergy following the same PCA SBRT clinical protocol. Three partial arcs (182°–300°, 300°-60°, and 60°-180°) with 2°/4° control-point spacing were used. The dosimetric difference between the VMAT and the original IMRT plans was analyzed. IMRT QA was performed for the VMAT plans using MapCheck2 in MapPHAN and the total delivery time was recorded. To mimic the treatment situation with ABC, where patients hold their breath for 20–30 seconds, the delivery was intentionally interrupted every 20–30 seconds. For each plan, the QA was performed with and without beam interruption. Gamma analysis (2%/2mm) was used to compare the planned and measured doses. Results: All VMAT plans with 2mm dose grid passed the clinic protocol with similar PTV coverage and OARs sparing, where PTV V-RxDose was 92.7±2.1% (VMAT) vs. 92.1±2.6% (IMRT), and proximal stomach V15Gy was 3.60±2.69 cc (VMAT) vs. 4.80±3.13 cc (IMRT). The mean total MU and delivery time of the VMAT plans were 2453.8±531.1 MU and 282.1±56.0 seconds. The gamma passing rates of absolute dose were 94.9±3.4% and 94.5±4.0% for delivery without and with interruption respectively, suggesting the dosimetry of VMAT delivery with ABC for SBRT won’t be compromised. Conclusion: This study suggests that PCA SBRT using VMAT with ABC is a feasible technique without compromising plan dosimetry. The combination of VMAT with ABC will potentially reduce the SBRT treatment time.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

SU-E-T-755: Timing Characteristics of Proton and Carbon Ion Treatments Using a Synchrotron and Modulated Scanning

Purpose: The time required to deliver a treatment impacts not only the number of patients that can be treated each day but also the accuracy of delivery due to potential movements of patient tissues. Both macroscopic and microscopic timing characteristics of a beam delivery system were studied to examine their impacts on patient treatments. Methods: 35 patients were treated during a clinical trial to demonstrate safety and efficacy of a Siemens Iontris system prior to receiving approval from the Chinese Food and Drug Administration. The system has a variable cycle time and can provide proton beams from 48 to 221 MeV/n and carbon ions from 86 to 430 MeV/n. A modulated scanning beam delivery technique is used where the beam remains stationary at each spot aiming location and is not turned off while the spot quickly moves from one aiming location to the next. The treatment log files for 28 of the trial patients were analyzed to determine several timing characteristics. Results: The average portal time per target dose was 172.5 s/Gy for protons and 150.7 s/Gy for carbon ions. The maximum delivery time for any portal was less than 300 s. The average dwell time per spot was 12 ms for protons and 3.0 ms for carbon ions. The number of aiming positions per energy layer varied from 1 to 258 for protons and 1 to 621 for carbon ions. The average spill time and cycle time per energy layer were 1.20 and 2.68 s for protons and 0.95 and 4.73 s for carbon ions respectively. For 3 of the patients, the beam was gated on and off to reduce the effects of respiration. Conclusion: For a typical target volume of 153 cc as used in this clinical trial, the portal delivery times were acceptable.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

SU-E-T-807: VMAT Vs. DIMRT Vs. SsIMRT Assessing the Dosimetric Parameters of Cervical Carcinoma Treatment with a 20-Patient Sample

Purpose: The purpose of this study is to assess the dosimetric parameters of cervical carcinoma treatment using 3 different radiation therapy delivery Methods: volumetric-modulated arc therapy (VMAT), the static-field dynamic multileaf collimator intensity-modulated radiation therapy (dIMRT) and the static-field step-and-shoot intensity-modulated radiotherapy (ssIMRT). Methods: Twenty patients with cervical carcinoma were selected to be planned with dual arc VMAT, dIMRT and ssIMRT using Monaco 3.3 TPS on the Axesse™ linear accelerator in this investigation. The total dose of the planning target volume (PTV) is 60Gy. The homogeneity index (HI), conformity index (CI), dose volume histograms (DVHs), delivery efficiency, dose of organs at risks (bladder, rectum, and femoral heads), were all measured. Results: Dose distribution in 3 different radiation therapy delivery methods satisfied clinical requirements. Mean HI of PTV with VMAT, dIMRT and ssIMRT is 1.08, 1.10, and 1.09 (p>0.05). Mean CI of PTV with VMAT, dIMRT and ssIMRT is 0.82, 0.8 and 0.8 (p>0.05). For the DVH of V10, V20 and V30 in bladder, there was a significant difference: VMAT>dIMRT=ssIMRT (p <0.05). For the DVH of V40 and V50, there was a significant difference: VMAT dIMRT >ssIMRT (p <0.05). Conclusion: The results show that VMAT has a great advantage in delivery efficiency than dIMRT and ssIMRT, without compromise to the PTV coverage, HI and CI. The delivery methods should be considered under the actual cervical carcinoma radiotherapy situation.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

TU-EF-210-00: Therapeutic Strategies and Image Guidance

The use of therapeutic ultrasound to provide targeted therapy is an active research area that has a broad application scope. The invited talks in this session will address currently implemented strategies and protocols for both hyperthermia and ablation applications using therapeutic ultrasound. The role of both ultrasound and MRI in the monitoring and assessment of these therapies will be explored in both pre-clinical and clinical applications. Katherine Ferrara: High Intensity Focused Ultrasound, Drug Delivery, and Immunotherapy Rajiv Chopra: Translating Localized Doxorubicin Delivery to Pediatric Oncology using MRI-guided HIFU Elisa Konofagou: Real-time Ablation Monitoring and Lesion Quantification using Harmonic Motion Imaging Keyvan Farahani: AAPM Task Groups in Interventional Ultrasound Imaging and Therapy Learning Objectives: Understand the role of ultrasound in localized drug delivery and the effects of immunotherapy when used in conjunction with ultrasound therapy. Understand potential targeted drug delivery clinical applications including pediatric oncology. Understand the technical requirements for performing targeted drug delivery. Understand how radiation-force approaches can be used to both monitor and assess high intensity focused ultrasound ablation therapy. Understand the role of AAPM task groups in ultrasound imaging and therapies. Chopra: Funding from Cancer Prevention and Research Initiative of Texas (CPRIT), Award R1308 Evelyn and M.R. Hudson Foundation; Research Support from Research Contract with Philips Healthcare; COI are Co-founder of FUS Instruments Inc Ferrara: Supported by NIH, UCDavis and California (CIRM and BHCE) Farahani: In-kind research support from Philips Healthcare.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

TU-EF-210-02: MRg Hyperthermia

60 APPLIED LIFE SCIENCES↗