Search

Current available secondary dose calculation software for Gamma Knife radiosurgery falls short in situations where the target is shallow in depth or when the patient is positioned with a gamma angle other than 90°. In this work, we evaluate a new secondary calculation software which utilizes an innovative method to handle nonstandard gamma angles and image thresholding to render the skull for dose calculation. 800 treatment targets previously treated with our GammaKnife Icon system were imported from our treatment planning system (GammaPlan 11.0.3) and a secondary dose calculation was conducted. The agreement between the new calculations and the TPS were recorded and compared to the original secondary dose calculation agreement with the TPS using a Wilcoxon Signed Rank Test. Further comparisons using a Mann‐Whitney test were made for targets treated at a 90° gamma angle against those treated with either a 70 or 110 gamma angle for both the new and commercial secondary dose calculation systems. Correlations between dose deviations from the treatment planning system against average target depth were evaluated using a Kendall’s Tau correlation test for both programs. The Wilcoxon Signed Rank Test indicated a significant difference in the agreement between the two secondary calculations and the TPS, with a P‐value

The field of radiation oncology has recently experienced a period of remarkable transformation of our technical capabilities. These technical and computational advancements have resulted in a tremendous improvement in our ability to precisely and accurately deliver radiation dose. However, this increased emphasis on technical capabilities may be inadvertently diverting attention and funding from scientific developments in other areas, even at a time when exciting new advances are occurring in cancer biology. Much of our recent technical development has been promoted and subsidized by the manufacturers of radiation oncology equipment. The question now becomes “who will encourage and subsidize the research needed to bring our recent biological advances to clinical fruition?” In a recent commentary which inspired this debate, Brown and Adler suggest that we “…are in a golden age of radiation and cancer biology” and that “…the industry's current focus on equipment development alone is undermining significant potential clinical advances in radiation oncology.”3 This is the subject of this month's 3DCRT debate. Arguing for the proposition will be Drs. Leonard Kim, Stephanie Markovina, and Samantha Van Nest. Dr. Leonard Kim has worked on defining microscopic disease target volumes for breast cancer radiotherapy at William Beaumont Hospital and Rutgers Cancer Institute of New Jersey. He is currently Chief Medical Physicist at the MD Anderson Cancer Center at Cooper. Dr. Stephanie Markovina is interested in improving therapeutic response to radiation in cervical cancer and other solid tumors by better understanding molecular mechanisms of radiation induced tumor cell death and survival. She is an Assistant Professor of Radiation Oncology and Cancer Biology at Washington University in St Louis where she specializes primarily in the treatment of patients with gynecologic cancers. Dr. Samantha Van Nest has worked to establish spectroscopic techniques for the personalization of radiation therapy. She is currently a Postdoctoral Associate at Weill Cornell Medicine in New York, where her research investigates the effects of radiation on tumor immunity, with a particular focus on improving our understanding of the abscopal effect. Arguing against the proposition will be Drs. Subarna Eisaman, Lakshmi Santanam, and Julie Sullivan. Dr. Subarna Hamid Eisaman is the clinical director and assistant professor at the University of Pittsburgh Medical Center (UPMC) Hillman Cancer Center Department of Radiation Oncology at the J. Murtha Pavilion in Johnstown, Pennsylvania. She serves as co‐chair of the Radiation Oncology Lung and Lymphoma Via Oncology Pathways Physician Advisory Committee. Her clinical practice includes treatment of breast, GYN, lung, CNS, head and neck, skin and musculoskeletal malignancies. Dr. Lakshmi Santanam is an attending medical physicist at Memorial Sloan Kettering Cancer Center. Her primary interests include motion management and patient safety. She currently serves as vice chair for the AAPM Working Group on RO‐ILS and the Task Group on the Management of Respiratory Motion in Radiation Oncology. Dr. Julie Sullivan is a biologist at the U.S. Food and Drug Administration's (FDA) Center for Devices and Radiological Health. Her scientific interests include the use of radiation‐emitting medical devices in clinical trials and the medical planning for and response to radiological and nuclear incidents.

Purpose Characterize the intra‐fraction motion management (IFMM) system found on the Gamma Knife Icon (GKI), including spatial accuracy, latency, temporal performance, and overall effect on delivered dose. Methods A phantom was constructed, consisting of a three‐axis translation mount, a remote motorized flipper, and a thermoplastic sphere surrounding a radiation detector. An infrared marker was placed on the translation mount secured to the flipper. The spatial accuracy of the IFMM was measured via the translation mount in all Cartesian planes. The detector was centered at the radiation focal point. A remote signal was used to move the marker out of the IFMM tolerance and pause the beam. A two‐channel electrometer was used to record the signals from the detector and the flipper when motion was signaled. These signals determined the latency and temporal performance of the GKI. Results The spatial accuracy of the IFMM was found to be

With the advancement of data-intensive technologies, such as image-guided radiation therapy (IGRT) and intensity-modulated radiation therapy (IMRT), the amount and complexity of data to be transferred between clinical subsystems have increased beyond the reach of manual checking. As a result, unintended treatment deviations (e.g., dose errors) may occur if the treatment system is not closely monitored by a comprehensive data transfer quality management program (QM). This report summarizes the findings and recommendations from the task group (TG) on quality assurance (QA) of external beam treatment data transfer (TG-201), with the aim to assist medical physicists in designing their own data transfer QM. As a background, a section of this report describes various models of data flow (distributed data repositories and single data base systems) and general data test characteristics (data integrity, interpretation, and consistency). Recommended tests are suggested based on the collective experience of TG-201 members. These tests are for the acceptance of, commissioning of, and upgrades to subsystems that store and/or modify clinical treatment data. As treatment complexity continues to evolve, we will need to do and know more about ensuring the quality of data transfers. The report concludes with the recommendation to move toward data transfer open standards compatibility and to develop tools that automate data transfer QA.

Purpose We describe the acceptance testing, commissioning, periodic quality assurance, and workflow procedures developed for the first clinically implemented magnetic resonance imaging-guided radiation therapy (MR-IGRT) system for real-time tracking and beam control. Methods The system utilizes real-time cine imaging capabilities at 4 frames per second for real-time tracking and beam control. Testing of the system was performed using an in-house developed motion platform and a commercially available motion phantom. Anatomical tracking is performed by first identifying a target (a region of interest that is either tissue to be treated or a critical structure) and generating a contour around it. A boundary contour is also created to identify tracking margins. The tracking algorithm deforms the anatomical contour (target or a normal organ) on every subsequent cine frame and compares it to the static boundary contour. If the anatomy of interest moves outside the boundary, the radiation delivery is halted until the tracked anatomy returns to treatment portal. The following were performed to validate and clinically implement the system: (a) spatial integrity evaluation; (b) tracking accuracy; (c) latency; (d) relative point dose and spatial dosimetry; (e) development of clinical workflow for gating; and (f) independent verification by an outside credentialing service. Results The spatial integrity of the MR system was found to be within 2 mm over a 45-cm diameter field-of-view. The tracking accuracy for geometric targets was within 1.2 mm. The average system latency was measured to be within 394 ms. The dosimetric accuracy using ionization chambers was within 1.3% ± 1.7%, and the dosimetric spatial accuracy was within 2 mm. The phantom irradiation for the outside credentialing service had satisfactory results, as well. Conclusions The first clinical MR-IGRT system was validated for real-time tracking and gating capabilities and shown to be reliable and accurate. Patient workflow methods were developed for efficient treatment. Periodic quality assurance tests can be efficiently performed with commercially available equipment to ensure accurate system performance.

Purpose: Magnetokinetic changes may affect crystal orientation and polymerization within the active layer of radiochromic film (RCF). This effect is investigated in a magnetic resonance image-guided radiotherapy unit within the context of film dosimetry. Methods: Gafchromic EBT2 RCF was irradiated in a 30 × 30 × 30 cm3 solid water phantom using a Co-60 MRI guided radiotherapy system (B = 0.35 T) under normal operating conditions, and under the exact conditions and setup without a magnetic field. Fifteen 20.3 × 25.4 cm2 EBT2 film sheets were placed at three different depths (d = 0.5, 5, and 10 cm) using five different treatment plans. The plans were computed using the MRIdian (ViewRay, Inc.) treatment planning system to deliver doses between 0 and 17.6 Gy. Films were analyzed before and after irradiation to obtain the net optical density (netOD) for each color channel separately. Scanning electron microscope (SEM) images were obtained to compare the active layer of selected samples. Results: The results indicated that the red channel netOD decreased between 0.013 and 0.123 (average of 0.060 ± 0.033) for doses above 2.8 Gy, with a linear increase in this effect for higher doses. Green channel netOD showed similar results with a decrease between 0.012 and 0.105 (average of 0.041 ± 0.027) for doses above 3.5 Gy. The blue channel showed the weakest effect with a netOD decrease between 0.013 and 0.029 (average of 0.020 ± 0.006) for doses above 8.0 Gy. SEM images show changes in crystal orientation within active layer in RCF exposed in a magnetic field. Conclusions: The presence of a magnetic field affects crystal orientation and polymerization during irradiation, where netOD decreased by an average of 8.7%, 8.0%, and 4.3% in the red, green, and blue channels, respectively. The under response was dependent on dose and differed by up to 15% at 17.6 Gy.

Purpose: To characterize the performance of the onboard imaging unit for the first clinical magnetic resonance image guided radiation therapy (MR-IGRT) system. Methods: The imaging performance characterization included four components: ACR (the American College of Radiology) phantom test, spatial integrity, coil signal to noise ratio (SNR) and uniformity, and magnetic field homogeneity. The ACR phantom test was performed in accordance with the ACR phantom test guidance. The spatial integrity test was evaluated using a 40.8 × 40.8 × 40.8 cm{sup 3} spatial integrity phantom. MR and computed tomography (CT) images of the phantom were acquired and coregistered. Objects were identified around the surfaces of 20 and 35 cm diameters of spherical volume (DSVs) on both the MR and CT images. Geometric distortion was quantified using deviation in object location between the MR and CT images. The coil SNR test was performed according to the national electrical manufacturers association (NEMA) standards MS-1 and MS-9. The magnetic field homogeneity test was measured using field camera and spectral peak methods. Results: For the ACR tests, the slice position error was less than 0.10 cm, the slice thickness error was less than 0.05 cm, the resolved high-contrast spatial resolution was 0.09 cm, the resolvedmore » low-contrast spokes were more than 25, the image intensity uniformity was above 93%, and the percentage ghosting was less than 0.22%. All were within the ACR recommended specifications. The maximum geometric distortions within the 20 and 35 cm DSVs were 0.10 and 0.18 cm for high spatial resolution three-dimensional images and 0.08 and 0.20 cm for high temporal resolution two dimensional cine images based on the distance-to-phantom-center method. The average SNR was 12.0 for the body coil, 42.9 for the combined torso coil, and 44.0 for the combined head and neck coil. Magnetic field homogeneities at gantry angles of 0°, 30°, 60°, 90°, and 120° were 23.55, 20.43, 18.76, 19.11, and 22.22 ppm, respectively, using the field camera method over the 45 cm DSV. Conclusions: The onboard imaging unit of the first commercial MR-IGRT system meets ACR, NEMA, and vendor specifications.« less

New technologies continue to be developed to improve the practice of radiation therapy. As several of these technologies have been implemented clinically, the Therapy Committee and the Quality Assurance and Outcomes Improvement Subcommittee of the American Association of Physicists in Medicine commissioned Task Group 147 to review the current nonradiographic technologies used for localization and tracking in radiotherapy. The specific charge of this task group was to make recommendations about the use of nonradiographic methods of localization, specifically; radiofrequency, infrared, laser, and video based patient localization and monitoring systems. The charge of this task group was to review the current use of these technologies and to write quality assurance guidelines for the use of these technologies in the clinical setting. Recommendations include testing of equipment for initial installation as well as ongoing quality assurance. As the equipment included in this task group continues to evolve, both in the type and sophistication of technology and in level of integration with treatment devices, some of the details of how one would conduct such testing will also continue to evolve. This task group, therefore, is focused on providing recommendations on the use of this equipment rather than on the equipment itself, and should be adaptable to each user's situation in helping develop a comprehensive quality assurance program.

The transfer of radiation therapy data among the various subsystems required for external beam treatments is subject to error. Hence, the establishment and management of a data transfer quality assurance program is strongly recommended. It should cover the QA of data transfers of patient specific treatments, imaging data, manually handled data and historical treatment records. QA of the database state (logical consistency and information integrity) is also addressed to ensure that accurate data are transferred. PACS numbers: 87.56.bd, 87.55.D, 87.55.Gh, 87.55.km, 87.55.Qr, 87.55.T

Purpose: The primary goal of this article is to formulate volumetric modulated arc therapy (VMAT) delivery problem and study interdependence between several parameters (beam dose rate, gantry angular speed, and MLC leaf speed) in the delivery of VMAT treatment plan. The secondary aim is to provide deliverysolution and prove optimality (minimal beam on time) of the solution. An additional goal of this study is to investigate alternative delivery approaches to VMAT (like constant beam dose rate and constant gantry angular speed delivery). Method: The problem of the VMAT delivery is formulated as a control problem with machine constraints. The relationships between parameters of arc therapy delivery are derived under the constraint of treatment plan invariance and limitations on delivery parameters. The nonuniqueness of arc therapy deliverysolutions is revealed from these relations. The most efficient delivery of arc therapy is then formulated as optimal control problem and solved by geometrical methods. A computer program is developed to find numerical solutions for deliveries of specific VMAT plan. Results: Explicit examples of VMAT plan deliveries are computed and illustrated with graphical representations of the variability of delivery parameters. Comparison of delivery parameters with that of Varian’s delivery are shown and discussed. Alternative delivery strategies such as constant gantry angular speed delivery and constant beam dose rate delivery are formulated and solutions are provided. The treatment times for all the deliverysolutions are provided. Conclusion: The investigations derive and prove time optimal VMAT deliveries. The relationships between delivery parameters are determined. The optimal alternative delivery strategies are discussed.

Purpose: We retrospectively evaluate the dosimetric impact of a 3.5% range uncertainty on CTV coverage and normal organ toxicity for a cohort of brain patients. Methods: Twenty treatment plans involving 20 brain cancer patients treated with Mevions S250 were reviewed. Forty uncertain plans were made by changing the ranges in original plans by ±3.5% while keeping all devices unchanged. Fidelity to the original plans was evaluated with gamma index. Changes in generalized equivalent uniform dose (gEUD) were reported for the following structures: CTV coverage, brainstem, optic chiasm, and optic nerves. Comparisons were made by plotting the relevant endpoints from the uncertain plans as a function of the same endpoints from the original clinical plan. Results: Gamma-index analysis resulted in a 50% pass rate of the uncertain plans using a 90% passing rate and 3%/3mm criterion. A 9.5% decrease in the slope of gEUD plot for the CTV was observed for the 3.5% downward range shift. However, the change in slope did not result in a gEUD change greater than 1.1% for the CTV. The slopes of the gEUD plots for normal structures increased by 3.1% 3.9% 2.4% and 0.2% for the chiasm, brainstem, left optic nerve and right optic nerve respectively. The maximum deviation from the gEUD of the clinical plan for normal structures was: 64% in the chiasm, 31% for the brainstem, and 19% for both optic nerves. Conclusion: A retrospective review shows moderate radiobiological impact of range uncertainty in passively scattered proton therapy with sporadic catastrophe. The linear regression analysis on the statistical data indicates a systematic deviation of gEUD from treatment planning in the light of range uncertainty.

Purpose: To implement image-guided proton therapy (IGPT) based on daily proton dose distribution. Methods: Unlike x-ray therapy, simple alignment based on anatomy cannot ensure proper dose coverage in proton therapy. Anatomy changes along the beam path may lead to underdosing the target, or overdosing the organ-at-risk (OAR). With an in-room mobile computed tomography (CT) system, we are developing a dose-based IGPT software tool that allows patient positioning and treatment adaption based on daily dose distributions. During an IGPT treatment, daily CT images are acquired in treatment position. After initial positioning based on rigid image registration, proton dose distribution is calculated on daily CT images. The target and OARs are automatically delineated via deformable image registration. Dose distributions are evaluated to decide if repositioning or plan adaptation is necessary in order to achieve proper coverage of the target and sparing of OARs. Besides online dose-based image guidance, the software tool can also map daily treatment doses to the treatment planning CT images for offline adaptive treatment. Results: An in-room helical CT system is commissioned for IGPT purposes. It produces accurate CT numbers that allow proton dose calculation. GPU-based deformable image registration algorithms are developed and evaluated for automatic ROI-delineation and dose mapping. The online and offline IGPT functionalities are evaluated with daily CT images of the proton patients. Conclusion: The online and offline IGPT software tool may improve the safety and quality of proton treatment by allowing dose-based IGPT and adaptive proton treatments. Research is partially supported by Mevion Medical Systems.

Purpose: Online adaptive therapy (ART) relies on auto-contouring using deformable image registration (DIR). DIR’s inherent uncertainties require user intervention and manual edits while the patient is on the table. We investigated the dosimetric impact of DIR errors on the quality of re-optimized plans, and used the findings to establish regions for focusing manual edits to where DIR errors can Result in clinically relevant dose differences. Methods: Our clinical implementation of online adaptive MR-IGRT involves using DIR to transfer contours from CT to daily MR, followed by a physicians’ edits. The plan is then re-optimized to meet the organs at risk (OARs) constraints. Re-optimized abdomen and pelvis plans generated based on physician edited OARs were selected as the baseline for evaluation. Plans were then re-optimized on auto-deformed contours with manual edits limited to pre-defined uniform rings (0 to 5cm) around the PTV. A 0cm ring indicates that the auto-deformed OARs were used without editing. The magnitude of the variations caused by the non-deterministic optimizer was quantified by repeat re-optimizations on the same geometry to determine the mean and standard deviation (STD). For each re-optimized plan, various volumetric parameters for the PTV, the OARs were extracted along with DVH and isodose evaluation. A plan was deemed acceptable if the variation from the baseline plan was within one STD. Results: Initial results show that for abdomen and pancreas cases, a minimum of 5cm margin around the PTV is required for contour corrections, while for pelvic and liver cases a 2–3 cm margin is sufficient. Conclusion: Focusing manual contour edits to regions of dosimetric relevance can reduce contouring time in the online ART process while maintaining a clinically comparable plan. Future work will further refine the contouring region by evaluating the path along the beams, dose gradients near the target and OAR dose metrics.

Purpose: To investigate the effects of magnetic fields in radiochromic films (RCF). Magnetokinetic changes may affect crystal orientation and polymerization within active layer of RCF, these effects are investigated in Magnetic Resonance Image-guided Radiotherapy (MR-IGRT). Methods: Gafchromic EBT2 RCF were irradiated in a 30×30×30 cm3 solid water phantom using a ViewRay MRIdian Co-60 MRI guided radiotherapy system (B=0.35 T). Fifteen 20.3×25.4 cm2 EBT2 film sheets were placed at three different depths (d=0.5, 5 and 10 cm) and irradiated using 5 different treatment plans. The plans were computed using the MRIdian treatment planning system to deliver 2, 4, 6, 8, and 10 Gy at a depth of 10 cm. The films were scanned using an Epson Expression 10000 XL flat-bed document scanner in transmission mode. Films were processed before and after irradiation to obtain a net optical density (netOD) for each color channel separately. Scanning electron microscope (SEM) images were obtained to compare the active layer of selected samples. Results: The results show the red channel netOD decreases between 1.3–12.3 % (average of 5.95 %) for doses above 2.8 Gy, with a linear increase in this effect for higher doses. Green channel netOD showed similar results with a decrease between 1.2–10.5 % (average of 4.09 %) for doses above 3.5 Gy. Blue channel showed the weakest effect between 1.3–2.9 % (average of 1.94 %) for doses above 8.0 Gy. SEM images show changes in crystal orientation within active layer in RCF exposed in a magnetic field. Conclusion: The presence of a magnetic field affects crystal orientation and polymerization during irradiation, decreasing netOD by an average of 5.95 % in the red channel. The under response is dependent on dose and differs by up to 12.3 % at 17.6 Gy. The results show that magnetokinetic effects should be carefully considered in MR-IGRT.

Purpose: There is growing recognition of need for increased clarity and consistency in the nomenclatures used for body and organ structures, DVH metrics, toxicity, dose and volume units, etc. Standardization has multiple benefits; e.g. facilitating data collection for clinical trials, enabling the pooling of data between institutions, making transfers (i.e. hand-offs) between centers safer, and enabling vendors to define “default” settings. Towards this goal, the American Association of Physicists in Medicine (AAPM) formed a task group (TG263) in July of 2014, operating under the Work Group on Clinical Trials to develop consensus statements. Guiding principles derived from the investigation and example nomenclatures will be presented for public feedback. Methods: We formed a multi-institutional and multi-vendor collaborative group of 39 physicists, physicians and others involved in clinical use and electronic transfer of information. Members include individuals from IROC, NRG, IHE-RO, DICOM WG-7, ASTRO and EORTC groups with overlapping interests to maximize the quality of the consensus and increase the likelihood of adoption. Surveys of group and NRG members were used to define current nomenclatures and requirements. Technical requirements of vendor systems and the proposed DICOM standards were examined. Results: There is a marked degree of inter and intra institutional variation inmore » current approaches, resulting from inter-vendor differences in capabilities, clinic specific conceptualizations and inconsistencies. Using a consensus approach, the group defined optimal formats for the naming of targets and normal structures. A formal objective assessment of 13 existing clinically-used software packages show that all had capabilities to accommodate these recommended nomenclatures. Conclusions: A multi-stakeholder effort is making significant steps forward in developing a standard nomenclature that will work across platforms. Our current working list includes > 550 structures. Outreach efforts are ongoing to ensure broader participation in evaluating and testing the principles as they are developed by TG263.« less

Patients treated using a magnetic-resonance image guided radiation therapy (MR-IGRT) system received both CT and MR simulations. During planning, the CT is used to determine relative electron density (RED) using a calibration table. This study aims to investigate the feasibility of MR-only treatments by comparing CT-computed dose distributions to those computed with combinations of water (1.0), lung (0.26), tissue (1.02), and bone (1.12) bulk RED overrides, and to identify the effects of the magnetic field on the RED-overridden doses. Methods: Four patients who received treatment using a commercial MR-IGRT system were analyzed (1 lung, 2 abdomen, and 1 pelvis). The clinical plans were computed using the first fraction MRI as primary, and the simulation CT as secondary for REDs. Plans were reoptimized using default bulk RED overrides (water/lung and tissue/lung for the lung patient, water/bone, tissue/bone, water only, and tissue only for the abdomen and pelvis patients). Additionally, each plan was re-optimized to include the static magnetic field. All plans were normalized to the same PTV coverage as the clinical plan. Dose-difference volumes and DVHs were computed for bulk density override plans, and 3D gamma analyses between each plan and its accompanying magnetic field plan were performed using 3%/3 mmmore » dose difference and distance-to-agreement criteria using the PTV and Skin as masking structures. Results: The average differences in PTV and organs-at-risk mean dose for all RED combinations tested were −0.19 Gy (−0.62 – 0.06 Gy) and −0.34 Gy (−1.76 – 0.33 Gy), respectively. The average PTV and Skin gamma pass rates for all RED combinations tested were 99.88% (99.5% – 100%) and 98. 35% (96.3% – 99.6%). No systematic differences in DVHs or isodoses were observed. Conclusions: It is likely that that a commercial MR-IGRT system may produce high quality treatment plans without the need for CT scans. Authors of this abstract are members of the Washington University Radiation Oncology department, which has a research agreement with ViewRay, Inc.« less

Purpose: In December, 2013 we treated our first patient with the Mevion S250 Proton Therapy System. This followed seven months of acceptance testing and commissioning, including; dosimetric data acquisition, safety checks, establishment of QA programs, mechanical and imaging checks, modeling validation, etc. Methods: The Mevion S250 possesses a compact synchrocyclotron attached to a gantry due to its small size (1.8m diameter) and light weight (22 tons). The system includes a 6D robotic couch allowing for any beam trajectory. The system provides 3D-2D imaging via fixed x-rays. Our TPS is Varian Eclipse, for which modeling and validation comprised most of the commissioning. The electronic medical record system is Elekta’s MOSIAQ 2.5, which provides connectivity for setup, imaging and treatment. Results: The modeling and validation met gamma of 3%/1mm for 98% of points. The imaging quality is superior than our other existing systems. Neutron dose was 95%. Over the first 14 months, for our first 150 cases, were predominantly; adult CNS, pediatrics (including CSI), lung, and liver. Thorax patients receive weekly scans for adaptive planning. Conclusion: The Mevion S250 has added a vital option to compliment our other modalities within our NCI Comprehensive Cancer Center.

Purpose: To develop a methodology for commissioning the real-time tumor tracking and beam control capabilities of a magnetic resonance imaging radiation therapy (MR-IGRT) system. Methods: The MRIdian (ViewRay, Inc., Oakwood Village, OH) MR-IGRT machine consists of a 0.35-T magnet and a three-head Co-60 delivery system capable of real-time sagittal plane acquisition at 4 frames per second (fps). After obtaining a volumetric MR image, a “target” is chosen by contouring an area of interest with different signal intensity than the surrounding medium. A “boundary” is created by expanding the target by some margin or using a previous contour. After a sagittal plane is chosen, during delivery the system deforms the target contour on each acquired plane, and compares it to the boundary - if the target contour is observed outside the boundary, the beam is turned off. Since the system uses no external or internal surrogates, careful tests of the individual system components had to be created and executed to characterize the accuracy and potential dosimetric errors associated with real-time gating on real anatomy. Results: Tests for spatial, temporal, and dosimetric accuracy were devised; these included latency, spatial integrity of the magnetic field, film, and ionization chamber measurements. A new set of phantoms was created, including a CIRS (Norfolk, VA) motion phantom that was modified to function in the magnetic field and have appropriate signal intensities. This phantom also included optical sensors that allowed for signal readout of its target position, and subsequent comparison to “beam off” signal on the heads. Boundary margins and other parameters were evaluated with film dosimetry by comparing the spatial distribution of the dose for static vs. gated deliveries. Ionization chambers were used to confirm an implemented shutter dose correction. Conclusion: The first commercially-available MR-IGRT system’s gating capabilities were characterized and successfully implemented in the clinic. Drs. Green, Kashani, and Mutic have held non-compensated consultant roles, received honoraria, and had travel expenses paid by ViewRay, Inc.

Purpose: To evaluate the need for adjusting the respiratory gating window on a daily basis due to variability of intrafraction motion of abdominal tumorstreated with stereotactic and conventional fractionated radiotherapy. Methods: Thirteen patients (8 with livercancer and 5 with pancreatic cancer) were implanted with visicoil fiducials and treated with amplitude based respiratory gated (RPM) radiation therapy on a Varian Trilogy linear accelerator (Varian Medical, Inc.). A total of 225 fluoroscopic movies were recorded using an Intrafraction Motion Review Software (Varian Medical, Inc.) over 106 fractions with an average length of ∼15s each. Intrafraction tumor motion was represented by the amplitude (peak‐to‐trough) of the fiducial motion trace extracted from each fluoroscopic movie. The superior‐inferior motion over the course of radiotherapy was compared to the maximum motion from 4D‐Computed Tomography (4DCT). Results: All patients showed predominant motion in superior‐inferior direction ranging from 1mm to 29 mm. The motion varied on a day to day basis, with changes of amplitude up to 6.7±5.4 mm for liver‐SBRT patients and 7.8±2.0 mm for pancreas‐fractionated patients. The maximum motion from 4DCT was compared to individual fractions for all patients. For liver‐SBRT patients, 4DCT overestimated the motion on 5/ 27 fractions (average 6.4 mm); and underestimated motion on 11/27 fractions (average 6.8 mm). For pancreas‐fractionated patients, 4DCT overestimated the motion on 60/79 fractions (average 13.6mm); and underestimated the motion on 16/79 fractions (average 7.9 mm). Conclusions: Observed intrafraction motion range varied from fraction to fraction and majority of treatment fractions (88%) were either overestimated or underestimated by 4DCT. These results suggest the need for daily respiratory gating window adjustment for a more accurate and efficient delivery.

Purpose: To describe a process for learning from radiation treatment plan(RTP) rejections by physicians and physicists for improvement of quality, safety, and efficiency of treatment planning. In our clinic IMRTtreatment plans are pre‐checked by physicists for technical and quality validation before review by the physician. Any problems identified during physics or physician reviews of RTPs offer an opportunity to identify systematic and random deviations and to develop tools, processes, and training to eliminate or reduce such problems in the future. We describe a process wherein the collection of plan rejections and related reasons is considered a part of normal process and not as additional work. Methods: In our clinic we use the DMAIC formalism for management of our operations, whereby processes are understood as comprising of define, measure, analyze, improve and control activities. Systematically quantifying plan rejections and the corresponding reasons offers an opportunity for improvement of treatment planning process and monitoring the effectiveness of corrective measures. This was accomplished through a set of features in our electronic whiteboards that seamlessly and effectively collect rejection information that were further analyzed for identification of improvement opportunities. Efficacy of any implemented improvement measures can then also be evaluated by quantifying future rejections. In this study we concentrate on plan rejections by physicists. Results: There were 110 plan rejections by physicists from September 2010 to Mar 2011. The rejections were due to plan‐quality, plan technical integrity and in some cases data‐entry errors. These rejections were used to identify systematic opportunities for training and better education and for design of in‐house developed auto‐planning and quality‐control scripts. Conclusions: Systematic and sustainable collection of treatment plan rejections for purposes of process improvement is possible. We have demonstrated that this data collection can be seamlessly integrated in normal treatment planning process through the use of electronic white boards.

Purpose: Electromagnetic tracking has been used to continuously monitor intra‐fraction prostate motion. We report on the commissioning of a clinical electromagnetictracking system with linear accelerator gating (DynamicEdge™GatingInterface, Calypso Medical Technologies, WA). Methods: Routinely, the motion of the Varian Respiratory Position Management(RPM) block, an external surrogate, is used for gating. With the Dynamic Gating Interface(DGI), the positions of the internal transponders implanted in the tumor are used for gating. The gating limits, defined as +/− thresholds in all three axes around the machine isocenter, define the beam on/off boundary, with a beam hold when the limit is exceeded. An in‐house developed 4D stage and a fixture containing three radiofrequency transponders were used for measurements. Beam stability, IMRT dose verification and latency were measured. The 4D stage was set to move in a repetitive sinusoidal pattern with peak amplitude of 1cm at 15 cycles per minute. For beam stability, the charge for non‐gated vs gated beam delivery was compared. For IMRT dose verification, a solid water phantom with films sandwiched between planes was used. A gating window (±0.2cm) was set for all five IMRT plans and gated dosimetric accuracy compared to static delivery. For latency measurements, a series of gated lateral MV integrated images were taken at an acquisition rate of 1fps. By knowing the actual motion trajectory measured with electromagnetic tracking, one can compare the trajectory of the gated integrated image to obtain latency. Results: The output stability for gated vs non‐gated fields was within 1%. For IMRT fields, on average 90% of the points passed the 3% dose, 3mm DTA criteria. The average system latency was measured to be within 281ms. Conclusions: The DGI has been commissioned and is being used clinically for prostate cancer patients to manage intra‐fraction motion. The latency may not currently be optimized for tumor sites exhibiting respiratory motion.

Purpose: Intensity-modulated adaptive radiotherapy (ART) has been the focus of considerable research and developmental work due to its potential therapeutic benefits. However, in light of its unique quality assurance (QA) challenges, no one has described a robust framework for its clinical implementation. In fact, recent position papers by ASTRO and AAPM have firmly endorsed pretreatment patient-specific IMRT QA, which limits the feasibility of online ART. The authors aim to address these obstacles by applying failure mode and effects analysis (FMEA) to identify high-priority errors and appropriate risk-mitigation strategies for clinical implementation of intensity-modulated ART. Methods: An experienced team of two clinical medical physicists, one clinical engineer, and one radiation oncologist was assembled to perform a standard FMEA for intensity-modulated ART. A set of 216 potential radiotherapy failures composed by the forthcoming AAPM task group 100 (TG-100) was used as the basis. Of the 216 failures, 127 were identified as most relevant to an ART scheme. Using the associated TG-100 FMEA values as a baseline, the team considered how the likeliness of occurrence (O), outcome severity (S), and likeliness of failure being undetected (D) would change for ART. New risk priority numbers (RPN) were calculated. Failures characterized by RPN ≥ 200 were identified as potentially critical. Results: FMEA revealed that ART RPN increased for 38% (n = 48/127) of potential failures, with 75% (n = 36/48) attributed to failures in the segmentation and treatment planning processes. Forty-three of 127 failures were identified as potentially critical. Risk-mitigation strategies include implementing a suite of quality control and decision support software, specialty QA software/hardware tools, and an increase in specially trained personnel. Conclusions: Results of the FMEA-based risk assessment demonstrate that intensity-modulated ART introduces different (but not necessarily more) risks than standard IMRT and may be safely implemented with the proper mitigations.

Purpose: The aims of this work are to describe the workflow and initial clinical experience treating patients with an MRI-guided radiotherapy (MRIGRT) system. Methods: Patient treatments with a novel MR-IGRT system started at our institution in mid-January. The system consists of an on-board 0.35-T MRI, with IMRT-capable delivery via doubly-focused MLCs on three 6 0 Co heads. In addition to volumetric MR-imaging, real-time planar imaging is performed during treatment. So far, eleven patients started treatment (six finished), ranging from bladder to lung SBRT. While the system is capable of online adaptive radiotherapy and gating, a conventional workflow was used to start, consisting of volumetric imaging for patient setup using visible tumor, evaluation of tumor motion outside of PTV on cine images, and real-time imaging. Workflow times were collected and evaluated to increase efficiency and evaluate feasibility of adding the adaptive and gating features while maintaining a reasonable patient throughput. Results: For the first month, physicians attended every fraction to provide guidance on identifying the tumor and an acceptable level of positioning and anatomical deviation. Average total treatment times (including setup) were reduced from 55 to 45 min after physician presence was no longer required and the therapists had learned to align patients based on soft-tissue imaging. Presently, the source strengths were at half maximum (7.7K Ci each), therefore beam-on times will be reduced after source replacement. Current patient load is 10 per day, with increase to 25 anticipated in the near future. Conclusion: On-board, real-time MRI-guided RT has been incorporated into clinical use. Treatment times were kept to reasonable lengths while including volumetric imaging, previews of tumor movement, and physician evaluation. Workflow and timing is being continuously evaluated to increase efficiency. In near future, adaptive and gating capabilities of the system will be implemented.

Purpose: The objective is to develop a rapid and comprehensive daily QA procedure implemented at the S. Lee Kling Proton Therapy Center at Barnes-Jewish Hospital. Methods: A scribed phantom with imbedded fiducials is used for checking lasers accuracy followed by couch isocentricity and for X-ray imaging congruence with isocenter. A Daily QA3 device (Sun Nuclear, FL) was used to check output, range and profiles. Five chambers in the central region possess various build-ups. After converting the thickness of the inherent build-ups into water equivalent thickness (WET) for proton, range of any beam can be checked with additional build-up on the Daily QA3 device. In our procedure, 3 beams from 3 bands (large, small and deep) with nominal range of 20 cm are checked daily. 17cm plastic water with WET of 16.92cm are used as additional build-up so that four chambers sit on the SOBP plateau at various depths and one sit on the distal fall off. Reading from the five chambers are fitted to an error function that has been parameterized to match the SOBP with the same nominal range. Shifting of the error function to maximize the correlation between measurements and the error function is deemed as the rangemore » shift from the nominal value. Results: We have found couch isocentricity maintained over 180 degrees. Imaging system exhibits accuracy in regard to imaging and mechanical isocenters. Ranges are within 1mm accuracy from measurements in water tank, and sensitive to change of sub-millimeter. Data acquired since the start of operation show outputs, profiles and range stay within 1% or 1mm from baselines. The whole procedure takes about 40 minutes. Conclusion: Taking advantage of the design of Daily QA3 device turns the device originally designed for photon and electron into a comprehensive and rapid tool for proton daily QA.« less

Purpose: A single-room proton system, the Mevion S250, was introduced into the arena of proton radiotherapy by Mevion Medical Systems. The first unit was installed and operates at the S. Lee Kling Proton Therapy Center at Barnes-Jewish Hospital. The objective of this abstract is to report the system's beam characteristics and Eclipse commissioning. Methods: Commissioning data were acquired for modelling longitudinal fluence, virtual source position, effective source position, source size and Bragg peaks in Eclipse. Stoichiometric CT calibration was generated via ICRU44 human. Spread-out Bragg peaks (SOBP) were measured with Parallel Plate Chamber and profiles with solid state detector for model validation. Heterogeneity effects were measured with bone and lung inserts in the beam line. RT dose was computed in a virtual water phantom, and exported from Eclipse to compare with measurements at various depths and axis. SOBPs were fine-tuned with partial shining correction and entry correction to match measurements. Output factor was measured for each individual field with an ADCL ion chamber in a water tank and fitted to a polynomial function to cross-check the monitor unit verification. Results: Ranges of all 24 options were measured within ±1mm tolerance. Modulations met a ±1mm or ±2% tolerance. SOBP flatness met a ±3% tolerance. Distal fall off (80%-20%) were measured between 6mm and 7mm for all options. Virtual source positions varied between 177cm and 195cm, decreasing with field size and range. SOBP generated by Eclipse agreed with measurements within ±3% in the entry region, and ±1%/±1mm in other regions. Sanity check for output achieved 5% accuracy in 98% of cases. Conclusion: The commissioning of the first Mevions S250 proton therapy system met specifications. The unit has been put in clinical operation since 12/17/2013.

Purpose: The Mevion S250 proton therapy unit is equipped with a 6D-robotic couch and IGRT system (Verity). The patient alignment process allows corrections in six degrees of freedom: translation {x,y,z}, pitch, roll, and yaw {θ,ϑ,ψ}. Geometric accuracy of couch corrections and imaging vs. radiation isocenter coincidence were quantified before clinical implementation. Methods: A commercial phantom with sixteen 2mm tungsten BBs was rigidly couch-mounted and imaged with CT. Seventeen rigid translations/rotations of known magnitude were digitally applied to the original CT image using commercial software, validated with Varian OBI system. For each altered image, phantom was mounted on robotic couch in original position, then Verity 2D:2D match (PA-LLAT) was performed using DRRs from altered images. Corrections were recorded and applied, phantom was imaged a second time and residual corrections recorded. Physical measurements verified that applied couch corrections coincided with both physical couch shifts/rotations and known CT image translations/rotations. Additionally, image vs. radiation isocenter coicidence was quantified over couch treatment angles (±90° from setup position) using radiochromic film and an image-guided couch star-shot. Posterior-anterior and left-lateral kV radiographs were taken before each beam was delivered to verify imaging/radiation isocentricity. Results: Verity suggested couch corrections and known CT shifts/rotations agreed within ±1mm (average: Δ lat=0.5mm; Δ vert=0.4mm; Δ long=0.3mm) and ± 0.4° (average: Δ pitch=0.24° Δ roll=0.01°; Δ yaw=0.10°). Physical couch measurements and Verity applied corrections agreed within ± 1mm (average: Δlat=0.5mm; Δvert=0.4mm; Δlong=0.2mm) and ±0.2° (average: Δpitch=0.03°; Δ roll=0.04°; Δ yaw=0.04°). The directionality of all translations and rotations were qualitatively verified. The image vs. radiation isocenter coincidence was

Purpose: Proton treatment planning systems are not able to accurately predict output factors and do not calculate monitor units (MU) for proton fields. Output factors (cGy/MU) for patient-specific fields are usually measured in phantoms or modeled empirically. The purpose of this study is to predict the output factors (OFs) for a given proton (R90) and modulation width (Mod) for the first Mevion S250 proton therapy system. Methods: Using water phantoms and a calibrated ionization chamber-electrometer, over 100 OFs were measured for various R90 and Mod combinations for 24 different options. OFs were measured at the center of the Mod, which coincided with the isocenter. The measured OFs were fitted using an analytic model developed by Kooy (Phys.Med.Biol. 50, 2005) for each option and a derived universal empirical-based polynomial as a function of R90 and Mod for all options. Options are devised for ranges of R90 and Mod. The predicted OFs from both models were compared to measurements. Results: Using the empirical-based model, the values could be predicted to within 3% for at least 90% of measurements and within 5% for 98% of the measurements. Using the analytic model to fit each option with the same effective source position, the predictionmore » is much more accurate. The maximal uncertainty between measured and predicted is within 2% and the averaged root-mean-square is 1.5%. Conclusion: Although the measured data was not exhaustive, both models predicted OFs within acceptable uncertainty. Both models are currently used for a sanity check of our continual patient field OF measurements. As we acquire more patient-field OFs, the model will be refined with an ultimate goal of eliminating the time-consuming patient-specific OF measurements.« less

Purpose: On‐board kilovoltage imaging is being used for accurate fiducial‐based alignment of tumors. However, these systems deliver additional dose to the patient and do not allow interactive repositioning with the therapist in the room. The purpose of this study is to measure and compare static localization accuracy of a commercial on‐board kilovoltage imaging system and a novel ACelectromagnetictracking system.Materials and Methods: A kilovoltage imaging system (Trilogy™ System, Varian, Palo Alto, CA) and an electromagnetictracking system (Calypso® 4D Localization System, Calypso Medical, Seattle, WA) which provides a continuous measurement of the implanted transponder positions, were compared for localization accuracy. A phantom containing three radiofrequency transponders was moved, using an in‐house developed 4D phantom (with a 0.4 mm position accuracy), in steps from 0.4 cm to 5 cm in the lateral, longitudinal, and vertical directions. The transponder positions were measured using the commercial matching software using antero‐posterior and lateral images and comparing against DRRs. These results were compared against the Calypso System measurements. Results: The localization accuracy, defined as the average difference of the measured positions (by the localization systems) to the actual positions (as determined by 4D‐ phantom positioning system) was found to be 0.0 ± 0.00 cm, 0.1 ± 0.1 cm and 0.1 ± 0.0 cm in three directions for KV system and 0.0 ± 0.0 cm for the Calypso system. Results showed that both systems provided excellent positioning accuracy.

Purpose: To quantify the potential impact of implementation of IHE‐RO Quality Assurance Plan Veto (QAPV) profile on patient safety of external beam radiation therapy operations. Methods: An institutional database of events (errors and near misses) was used to evaluate the ability of QAPV to prevent the clinically observed events.. We analyzed those reported events which were related to inconsistencies between DICOM RT plan parameters between the intended treatment (treatment planning system) and the delivered treatment (treatment machine). Critical DICOM RT plan parameters were identified. Each event was scored for importance using the Failure Mode & Effects Analysis (FMEA) methodology. Potential error occurrence (frequency) was derived based on the collected event data, along with the potential event severity, and probability of detection with and without the theoretical implementation of QAPV plan comparison check. FMEA Risk Priority Numbers (RPNs) with and without QAPV were compared to quantify the potential benefit of clinical implementation of QAPV. This analysis considered the highest risk parameters with RPN>200. Results: The clinical implementation of the IHE‐RO QAPV reduced RPN scores to below 200 for 7 (out of 8) high‐risk parameters. For example, RPN values reduced from 324 to 108 for ‘beam MU's’ inconsistencies, 288 to 96 for ‘treatment machine’ inconsistencies, 200 to 40 for ‘beam limiting device type’ inconsistencies, and 252 to 72 for ‘wedge’ inconsistencies. Conclusion: This analysis quantifies the value of the IHE‐RO QAPV implementation in clinical workflow. We demonstrate that although QAPV does not provide a comprehensive solution for error prevention in radiation therapy, it can have a significant impact on a subset of the most severe clinically observed events.

Integrating the Healthcare Enterprise in Radiation Oncology (IHE‐RO) is an ASTRO sponsored initiative, composed of vendors, physicists and clinicians dedicated to improving equipment and software integration issues related to radiation treatment. The objective of this initiative is to improve the way computer based systems in radiation oncology share information using well‐defined data exchange standards (DICOM / HL7). The Radiotherapy process requires integration of software and hardware from a variety of vendors using a multitude of systems. For this integration to be done successfully a series of data transfers must occur with 100% fidelity and reliability. Here there can be a significant problem of lack of interconnectivity and interoperability of electronic infrastructure. The follow‐up care of radiation oncology patients extends over time and multiple care facilities. Therefore, it is critical that all patients' healthcare data be readily available on demand to individuals and their changing healthcare providers. The IHE‐RO initiative has solved several interconnectivity and interoperability issues amongst Treatment Planning Systems, Treatment Management Systems and Treatment Delivery Systems. However, it is not easy for end users to discern the lack of interconnectivity amongst RT devices available in the market place. IHE‐RO testing events and test tools have enabled vendors to successfully test and demonstrate interoperability between their products. These solutions will improve patient safety in concordance to the ASTRO ‘Target Safely’ initiative in addition to improving workflow efficiency in the clinic.In 2004, ASTRO formed a multi‐society, multi‐national, and multi‐specialty IHE‐RO task force to address issues of interoperability and information sharing between various healthcare systems in radiation oncology and is working to resolve them in a systematic way using established industry standards. The IHE‐RO task force consists of a planning committee (PC) and a technical committee (TC). The membership of these committees along with schedules of activities, meeting agendas and minutes, and working documents can be found on the IHE Wiki at http://wiki.ihe.net.This lecture will provide an overview of the activities of IHE‐RO and how this initiative has helped the Radiation Oncology community to solve the interoperability issues of the clinic. Learning Objectives: 1. Understand the history of IHE‐RO and the need behind it. 2. Review current IHE‐RO Profiles & user cases and how they help solve interoperability issues in the clinic. 3. Understand the future direction of IHE‐RO and how you can contribute to its success. Partial funding from ASTRO

Purpose: To determine the effect of the magnetic field on surface and buildup dose in radiotherapy using MR‐IGRT, specifically measured with a Co‐60 system. Methods: A commercially‐available MR‐IGRT system was used to measure surface, peripheral, and build‐up dose due to thermoplastic head immobilization masks. Both radiographic (Kodak EDR2) and radiochromic (EBT2) film types were used for surface measurements. A small‐volume ionization chamber was used for peripheral dose measurements. Several types of thermoplastic masks from three different manufacturers were chosen; radiochromic film was used to measure possible dose to skin under the masks. Comparisons were made using these masks with 6‐MV photon beams delivered by a Varian Truebeam machine. Results: For a 10×10 cm field size at 100 SSD, the surface dose as normalized to maximum dose (at 0.5 cm) was determined to be about 30% as measured by both EDR and EBT2 films. Peripheral dose with an open 10x10 field at 10 cm depth matched previously published data for Co‐60. Skin dose due to thermoplastic mask buildup was at least 30% higher (depending on mask construction) with Co‐60 as compared to 6‐MV due to its lower energy. Conclusion: While the magnetic field of an integrated MR‐IGRT system is expected to reduce skin dose by sweeping away contamination electrons, the use of Co‐60 introduces the added challenge of carefully choosing immobilization devices in order to preserve the skin‐sparing effect of the MR. Drs. Green, Hu, and Mutic have served as consultants to ViewRay, Inc.

Purpose: Traditional manual quality assurance checks of a patient treatment plan beam parameters transfer involve visually checking the information printed from the treatment planning system against the record‐and verify system for one‐to‐one correspondence. To provide the efficiency and accuracy of data transfer check, we have utilized the Varian TrueBeam log files which contain the complete delivery parameters. Methods: The approved plans are transferred to the Record and Verify (R&V) system, and the beams are delivered in the Truebeam Linac. The expected and actual status of TrueBeam delivery parameters are recorded during the delivery. Compared to traditional dynalog files from Varian, TrueBeam log files offer complete delivery parameters, which enable complete data transfer QA. An automatic program was designed to read the planned parameters from TPS and delivered parameters from Linac workstation. The program can verify the delivered parameters for all the external deliveries, including 3D conformal, EDW delivery, IMRT, VMAT, and electrons treatments. Results: The patient ID, beam ID, photon or electron energy, beam MU, gantry angle, couch angle, cough positions, collimator angle, jaw positions, EDW wedge angle and orientations, MLC positions, number of segments, gantry speed, dose rate, applicator size are all checked. The data transfer and/or delivery errors are flagged in the report for each type of delivery. Conclusion: The end‐to‐end data transfer check using TrueBeam log files provides an efficient, reliable and complete beam parameter plan check process for variety of radiation delivery technique. It is more efficient than human chart checking and improves the robustness and quality of chart checking.

Purpose: Traditional IMRTquality assurance (QA) methods are incapable of providing complete information about IMRT delivery. Most methods consist of a planar film or diode array measurement for relative dosimetry and 1 ‐2 ionization chamber (IC) measurements made in a homogeneous medium for absolute dosimetry. A new model‐ and measurement‐based IMRT QA tool makes 3D delivered‐dose verification possible through independent dose calculation and 2D fluence measurements, which combine to provide reconstructed dose on a 3D heterogeneous patient dataset. This work aims to commission this new IMRT QA tool and validate its performance relative to traditional QA methods. Methods: The COMPASS system (IBA Dosimetry) consists of a software package for dose calculation and visualization/analysis of measured data acquired using a gantry‐mounted MatriXX Evolution detector array (1020 ICs) and gantry angle sensor. Commissioning included modeling a Varian Truebeam 6 MV photon beam. The system computation algorithm was validated via direct comparison of the COMPASS and Pinnacle‐TPS calculated dose distributions for twelve previously‐treated patient plans (sites: lung, breast, pancreas, head and neck, prostate; delivery types: SMLC‐DMPO, SmartArc). These same plans were measured at the actual treatment beam angles using both the gantry‐mounted MatriXX detector and two ICs placed in a standard cuboidal IMRT solid‐ water phantom. The COMPASS reconstructed dose was validated by comparison of the average PTV dose to the average IC dose measurement, each relative to the TPS expected dose. Results: The COMPASS calculated dose differed from the TPS calculated dose by 0.71+\−0.37%. On average, the measured dose differed from the TPS expected dose by 2.04+\−0.93% for COMPASS and 1.45+\−0.94% for the ICs. Conclusion: The COMPASS computation algorithm is valid and the measured results are comparable with those of the traditional IMRT QA method, while providing more dosimetry information (absolute and relative) in a single measurement and taking patient tissue heterogeneity into account.

Purpose: The changes in the head design of the new Varian TrueBeam compared to the C‐series linear accelerators, required modification of the electron scattering foils and their placement in the beam line. As a result, the electron beam characteristics cannot be matched to existing Varian accelerator models (C‐series). Extensive measurements were needed for determining the beam characteristics for comparison and for commissioning purposes. We present a detailed analysis of the various dosimetric parameters measured for Truebeam compared to C‐series linacs. Methods: A Wellhoffer scanning system was used to measure PDDs and profiles at various depths and source to surface distances (SSD) for all applicators and all energies. Output measurements were performed for all electron applicators and different blocks with field sizes ranging from 2×2 to 15×15 cm depending on the applicator, at standard and extended SSDs, using a 0.03 cc ionization chamber (IBA Dosimetry CC04 chamber) in water, at the dmax depth for each energy. In‐air measurements of cross‐plane profiles were performed using a scanning system, to determine the effective SSD and electron dispersion (sigma‐theta‐x) which describes the angular scattering of electrons. Results: No significant changes were observed in the PDDs between the two accelerator systems. The effective SSD increased as a function of energy by 0.6 to 2.5 cm for TrueBeam (25×25 cm applicator), while the electron dispersion factor showed no change. The change in output factors was most significant for large applicators (20×20 and 25×25 cm), and low energies ranging from 1.5 to 6%. This difference increased systematically with increasing SSD. Conclusions: The changes in the electron beam parameters of the Varian TrueBeam compared to the C‐series linacs are significant enough to require unique modeling of electrons in our treatment planningsystem, as well as unique output factors for monitor unit calculations.

Purpose: To develop an infrastructure to perform digital, automatic, intelligent, process‐oriented, and patient safety‐oriented quality control in radiation oncology. To leverage an electronic infrastructure to use advanced information processing techniques, proactive quality control tools, employ automated and intelligent systems and facilitate standardization, data sharing & benchmarking in radiation oncologyquality control program Method: An web based centralized data management system called Mallinckrodt Institute of Radiology Quality AssuranceInformation System ( MIR‐QAIS) was developed to collect manage and analyzequality assurance data. Several tools that could leverage the electronic environment was developed such as automated quality control for patient specific IMRT delivery, electronic chart checking, workflow monitor and manager, status reporting with dashboards, calculation based quality assurance,data mining tools for data informatics, document management component, incident reporting for organizational learning etc. This infrastructure has facilitated us to go completely paperless including all quality assurance tasks. Also all the test that are in developed is to perform quality control rather than quality assurance. The infrastructure was designed for easy record keeping, auditing, and compliance and to facilitate standardization and benchmarking. Results: We have developed a web based infrastructure to practice quality control in radiation oncology. Several tools were developed leveraging this infrastructure. Web‐based QA documents for Machine QA with statistical analysis tools, alerts and warnings, Dynalog based automated patient specific QA, Electronic chart check, automatic QA plan generation through scripts, intelligent review of plan quality, technical aspects of plan and logical consistency using scripts are to name a few. Conclusion: The electronic web based QAIS infrastructure has facilitated and would continue to aid in developing effective quality control program to practice better and safer radiation therapy.

Purpose: To evaluate the adequacy of constant dose rate (CDR) VMAT plans for clinical use of commonly treated sites. The clinical acceptability of CDR VMAT plans was evaluated based on plan quality comparisons against clinically used IMRT plans. Methods: Several patient treatments planned using IMRT were considered for the study and replanned using Pinnacle 9.0 (SmartArc) treatment planning system. Several clinical sites were considered for this study — prostate and prostate bed (4 patients), pelvis (1), breast (1) and head and neck (H&N) (2). The quality of CDR plans normalized to PTV mean dose was compared against static field IMRT plans based on dose conformality, planning target volume (PTV) coverage and dose volume histograms (DVHs) of organs at risk (OAR). Results: Plan qualities of prostate, prostate bed and pelvis plans were evaluated based on rectum and bladder DVHs, PTV coverage and dose conformality. Prostate and prostate bed: CDR plan was found to be clinically acceptable with better OAR sparing and delivery time. Pelvis: CDR plan was lacking coverage and conformality and didn't have a significant advantage over the IMRT plan. Breast: Plan quality was evaluated based on PTV coverage, isodose conformality and DVHs generated for OARs — lungs,heart and cord. The CDR plan was clinically unacceptable, primarily due to low doses (

Purpose: Currently, electromagnetic tracking cannot be done inside a CT scanner. We wanted to determine if wireless electromagnetic tracking can be performed accurately in the CT environment. Method and Materials: A research version of the Calypso® 4D Localization System™ (Calypso Medical Technologies, Seattle, WA) was utilized in a Brilliance Big Bore CT scanner (Philips Healthcare, Cleveland OH) with the carbon fiber table removed. Three transponders were oriented vertically (Z orientation) or parallel (Y orientation) to the sensor array and fixed at 20cm below the array. Standard deviation of the positioning data was observed and comparison was made for array position high (toward the top of the gantry) versus low, array gain high versus low, transponder orientation Y versus Z. 60 seconds of tracking data was collected for each measurement. The standard deviation was used to determine precision, and the transponders were imaged with the CT scanner to determine accuracy. Standard deviation below 0.2 cm was considered appropriate for clinical use. Results: The standard deviation became higher when distance between array and transponders increased. The system performed best when array position was low, beacon orientation in the Y axis, and sensor gain set to low. In all cases with the array position low and array gain low, the system met the clinical goal of standard deviation less than 0.2 cm for a 12×12×12 cm3 volume. Conclusion: This work describes the first electromagnetic tracking system that works in a CT environment. Potential applications include using implanted transponders to guide correlated imaging measurements of respiratory motion (‘tumor correlated imaging’ versus ‘respiratory correlated imaging’) as well as wireless tools for intervention procedures in the CT bore. Further mechanical work will be necessary to optimize the ergonomics, and signal processing work to optimize the performance, of a combined tracking/imaging system. Conflict of Interest: Calypso Medical

Purpose: A novel electromagnetictracking system is being used for real‐time tracking during treatment delivery. On board cone‐beam CTimaging is routinely being used for real‐time imaging and localization. Concurrent use of these two modalities might prove beneficial for correlating imaging and tracking information. The purpose of this study is to investigate the effect of the presence of the electromagnetictracking system on the CBCTimage quality. Method and Materials: A commercial CT performance phantom (Catphan, Phantom Laboratory, Salem, NY) containing various image quality assessment tools was imaged using a kilovoltage on‐board cone‐beam CT system (Varian Medical Systems, Palo Alto). An electromagnetictracking system (Calypso® 4D Localization System, Calypso Medical, Seattle, WA) uses an electromagnetic array for tracking transponder positions. The imaging quality assessment phantom was imaged with and without the electromagnetictracking system in place. To quantify the effect on the image quality, the CT number accuracy, spatial integrity, image uniformity, high and low contrast resolution were compared. Results: CT number accuracy, spatial linearity and high contrast resolution were unaffected by the presence of the array. The visibility of the 1% cylindrical low contrast resolution targets was 15 mm and 7 mm for with and without the array respectively. The inherent streaking artifacts degraded the low contrastimage quality significantly. Conclusion: Presence of an electromagnetic array significantly degrades CBCT low contrast resolution while other image performance parameters are minimally affected. For imaging human anatomy, algorithms to improve image quality may need to be developed. Conflict of Interest: This work is supported in part from a grant from Calypso Medical Systems.

Purpose: To develop a general image processing and dose computation procedure that allows for the accumulation of accurate dose distributions for purposes of both outcome research and IG‐ART (image guided adaptive radiation therapy). We applied the procedure to cone‐beam CT head‐neck cancertreatment cases, as well as Tomotherapy MVCT (mega‐voltage CT) GYN and prostate cancertreatment cases. Method and Materials: The image processing procedures include preprocessing, rigid and deformable registration, mesh‐ based structure contour propagation, and image volume composition for dose re‐computation. The dose processing includes dose recomputation on the daily CT or the composed CT volume, deforming and register the daily dose to the planning dose space, dose accumulation, evaluating of the accumulated dose against the planned dose. Accuracy of image registration is very important for the entire procedure because it determines the accuracy of all later subsequent steps. In order to improve the accuracy, we preprocessed the CTimages before the registration step by using various methods, including edge‐preserving smoothing, Gaussian lowpass smoothing, contrast enhancement, window‐level intensity transformation, and bowel gas pocket painting for abdominal regions. We used MI (mutual information) based algorithm for rigid image registration, and applied the Horn‐Schunck optical flow algorithm for deformable image registration. We used a mesh‐based algorithm for structure contour deformation, interpolation and smoothing. Results: By applying these preprocessing procedures we were able to achieve improved image registration results. The computed image deformation fields were then used to propagate the structure contours from the kVCT to the current daily CTimage, which could be used for dose deformation or re‐computation. Conclusion: We have developed a procedure of image processing and dose computation to support the accumulation of ‘true’ dose distributions. These methods could be used in both radiotherapy outcome research and adaptive radiotherapy applications. Partially supported by NIH R01 grant CA85181.

Purpose: The objectives of this study are to describe the 4D treatment planning process for moving targets and to evaluate the dosimetric consequences caused by target motion during tomotherapy delivery. Method and Materials: A lungcancer patient was CT scanned using our standard 4D‐CT protocols on Phillips brilliance 64 slice CT scanner. A maximum intensity projection CT dataset was used for treatment planning.Tumor motion trajectory and amplitude was determined from the inhale and exhale phases of the 4DCT. A three‐dimensional motion pattern was created by scaling the breathing form to an average magnitude of the target motion. The three‐dimensional trajectory was programmed into the Washington University 4D Phantom to simulate target motion. Eight EDR2 films were loaded into a phantom for dosimetric verification. Measurements were performed on a static phantom and then repeated on the oscillating phantom. Experiments were repeated for their reproducibility. Films were analyzed using Hi‐Art TPS. Results: To quantify the dose errors, gamma analysis was performed. In static phantom study, >97% of the points passed with a gamma criteria of 3% and 3mm. When the same criterion was applied for the oscillating phantom, 15–25% of the points failed. When the gamma threshold was increased to 8% and the gamma analysis window was tailored to be within the CTV, >98% of the points passed indicating that the dose errors are of the order of 5% for majority of the points. In order to find the maximum dose errors, the tolerance was increased until 100% of points passing the criteria. Conclusion: 4D treatment planning process for helical tomotherapy is discussed. Gamma analysis revealed that, the dose errors are of the order of 5% for majority of the points and the maximum dose error within the CTV was 11%. This work is supported in part by Tomotherapy Inc.

Purpose: An automated portal vision based quality assurance method is implemented to replace the labor intensive manual used to ensure the collimator alignment accuracy prior to performing stereotactic radiosurgery.Method and Materials: We use Varian PortalVision™ EPID on a Varian Trilogy™ linear accelerator to acquire the projection images of an isocentrically‐placed tungsten sphere produced during Winston‐Lutz Alignment Test that includes multiple gantry and couch combinations. The analysis routine applied to each acquired image consists of 1) search for the sphere and collimator edges 2) fitting them to a circle and 3) calculation of distance between the collimator and sphere optimized center points. The method, based on the properties of pseudo‐inverse matrices, is implemented to calculate the cumulative 3D shift of the sphere center relative to the isocenter of the Trilogy machine. The graphic interface was created using MatLab™ that permits the choice of the type of the QA procedure (daily or weekly), performs image analysis and allows visual examination, saving and printing of the results. Results: The in‐house software was tested in 17 trials by comparing it to the conventional SRS QA technique based on film image acquisition with subsequent manual shift measurements. The calculated mean of the difference between film and portal vision — based methods was: 0.07±0.11mm vertical, −0.11±0.17mm lateral, 0.02±0.08 mm longitudinal shift components. The mean of 0.11±0.13 mm was shown for the absolute value of the vector shift differences in 3D. Conclusion: The automated QA procedure for SRSLINAC QA is created, tested and proven to be fast, precise and efficient replacement for the conventional film‐based quality assurance technique. The use of the presented routine should allow more frequent SRS QA tests, which ensures high accuracy and quality of the patient treatments. Conflict of Interest: Partial support by Varian Medical Systems, Inc. acknowledged.

Purpose: A graphical and quantitative procedure for amplitude‐gated treatment planned using phase based 4DCT of free breathing patients using the Varian RPM gating system has been developed as a part of the study of phase and amplitude based imaging and treatment. There are several phase‐based CT scanning systems that produce phase‐based images for gated treatments, but for free breathing phase may not be a reliable predictor of tumor location. Good correlation has been shown between abdomen height and diaphragm position, making it a promising treatment modality. Method and Materials: A phase‐based retrospective CT scan from a Philips large bore 16 slice CT scanner is obtained and the phase markers are adjusted to delineate actual breaths. A gating window that is a subset of the whole CT scan is set and a visual representation of gated motion called a MIP(maximum intensity projection) is created to visualize any anatomical excursions. The Varian RPM data is then compared with the scan data to quantify the actual marker block motion(or chest height) during the gating window as well as for an entire phase. The scan data is then presented not only as a percentage of an average breath, but as a chest height range within the total. This information is checked on treatment days and adjusted if necessary. The gating signal and fluoroscopy are compared to a 4D DRR generated from the MIP to check for geographic as well as systematic misses. Before treatment a gated port film (gated over several breaths and dose limited) can be captured to verify gating of the treatment beam. Results: For phantom based studies of regular breathing the method is robust. The model converts phase to amplitude of abdomen height. Conclusion: This method can validate a gated treatment using different imaging modalities.

Purpose: The Calypso® Medical 4D Localization system is capable of tracking real‐time dynamic motion without ionizing radiation. A limitation of any fiducial based system is the inability to visualize surrounding tissues. Cone beam CT(CBCT) of moving objects results in image blurring due to long acquisition times. We investigated the use of the Calypso® 4D localization system to improve motion artifacts obtained from the Varian Trilogy CBCT.Materials and Methods:. A research Calypso® 4D tracking system was installed in a Varian Trilogy vault. A rectangular phantom with implanted transponders was attached to an internally‐developed 4D stage. A CBCT was obtained while moving the phantom under the Calypso® measurement array using a patient tumor derived trajectory. The projection images were obtained and shifted using the corresponding Calypso® transponder positioning information and then reconstructed into CBCTimages. This process was repeated for a dog with transponders implanted in the lung as part of an IRB‐approved study. Results: The Calypso® based image shifts caused the radiographic projection of the transponders remained stable in sinogram space. CBCTimages from the shifted sinogram exhibited reduced image motion artifacts. Without artifact reduction, the transponders were visualized as multiple streaks and the surface of the phantom was heavily deformed. With artifact reduction, the transponders were accurately localized, and the deformation was removed. The dog's breathing cycle made qualitative image motion artifact reduction review difficult. Quantitative analysis of the reconstructedCT numbers showed sharper gradients through the transponders, indicating that the shifting process had improved the image quality. Conclusions: Use of a wireless electromagnetic implanted transponder system for motion correction of CBCT is possible. This preliminary sinogram shifting technique was very effective for non‐deforming objects. Further work will increase the synergy between real‐time tracking systems and volumetric imaging. This work was supported by Calypso® Medical Technologies.

Purpose: On‐board cone‐beam imaging is being used to collect kilovoltage CTimages for treatment position verification and analysis of tumor response. One challenge of cone‐beam imaging is that full sinogram acquisition takes more than 1 minute. While breathing motion in the lungs, influence both cone‐beam and fan‐beam modalities, its profound effects in cone‐beam CT are well known. However, there are many portions of the body where voluntary and involuntary processes can yield small motions. The purpose of this study is to investigate the influence of small motions on cone‐beam reconstruction quality. Materials and Methods: A commercial CT performance phantom (Catphan, Phantom Laboratory, Salem, NY) containing various image quality assessment tools was imaged using a kilovoltage on‐board cone‐beam CT system (Varian Medical Systems, Palo Alto). The imaging phantom was moved using an in‐house developed “4D phantom” (with a 0.4 mm position accuracy), in sinusoidal patterns with amplitudes of 1.25mm and 2.5 mm in the three orthogonal directions and elliptical patterns with axes from 1 mm to 2.5 mm in steps of 0.5 mm. To quantify the effect on the image quality, the CT number accuracy, spatial integrity, image uniformity, high and low contrast resolution were compared. Results:CT number accuracy and spatial linearity were unaffected by motion. While single‐dimensional motion did not affect the low‐contrast resolution, elliptical motion yielded degradation. The visibility of the 1% cylindrical low contrast resolution targets was 7 mm, 8 mm and 15 mm for static through 1 mm, 2.0 mm, and 2.5 mm ellipses. High contrastspatial resolution was improved slightly for in‐plane motion, but degraded sharply with out‐of‐plane motion. Conclusions: This information will allow investigators to evaluate the ultimate utility of cone‐beam imaging for imaging studies when patient immobilization is not perfect.

Purpose: Tomotherapy is a form of intensity modulated radiation therapy(IMRT) that utilizes rotating fan beams modulated by a binary‐multileaf collimator. The radiation is delivered either serially or helically as the patient is moved in a craniocaudal sequence for tumor coverage. While Tomotherapy can deliver highly conformal dose distributions, it yields the lowest delivery efficiency (tumordose per MU) of current IMRT‐delivery options. This relatively low efficiency has the potential for delivering high total‐body doses due to head leakage, so a quantitative evaluation of the whole‐body dose is warranted. Methods and Materials: We conducted this evaluation for a dedicated helical Tomotherapy delivery device (Hi‐Art System®, Tomotherapy Inc) and compared the results against the previously published serial Tomotherapy system (Corvus, NOMOS Corporation) and traditional IMRT whole‐body data. A typical head‐and‐neck treatment plan (2Gy per fraction, 6622MU) was prepared and delivered to a large water‐equivalent phantom. An ADCL‐calibrated large‐volume ionization chamber (A17 Exradin) was used to measure the low doses. The dose was measured at both 1.5cm (dmax) and at the center of the phantom. Results: From 10cm to 48cm from the inferior target edge (the most proximal serial tomotherapy point was at 10 cm), the helical tomotherapy dose was less than 0.5% of the target dose, and was between 20% and 30% of the serial tomotherapy leakage dose. This study showed that the whole‐body dose for the 70Gy is approximately 140mSv. This dose is less than the 560mSv for a 70Gy treatment as published by Followill, et al. (Int.J.Radiat.Oncol.Biol.Phys. 38, 667). Conclusions: This study indicates that the commercial helical Tomotherapy system provides less whole‐body dose than serial Tomotherapy or conventional IMRT. This is probably due to the internal linear accelerator shielding design and the use of 6 MV photons. This work was supported in part by funding from Tomotherapy, Inc.

Purpose: Multiple technologies are being utilized to improve real‐time tumor tracking. To date, there have not been methods to prospectively compare different technologies with realistic tumor trajectories. We evaluated the capabilities of the Calypso® Medical 4D Localization System (Calypso Medical, Seattle, WA) and Varian Trilogy System (Varian Medical Systems, Palo Alto, CA) fluoroscopy in tracking dynamic objects. Method and Materials: Initially, a quality assurance fixture containing three implantable transponders was moved by an in‐house developed 4D phantom through an ellipse and a non‐uniform human lungtumor path modeled with CTimaging and spirometry. Subsequently, three transponders that had been implanted in a canine lung were tracked. In both experiments, the transponders were fluoroscopically imaged on a Trilogy system while simultaneously being tracked by the Calypso® 4D localization system. The fluoroscopic images were recorded and later analyzed using a custom‐written (MATLAB) image processing program to determine the transponder projection positions with respect to time. The trajectories derived from the fluoroscopic images were synchronized with and compared to the Calypso System position data. Results: The root mean square (RMS) position differences were less than 0.03 mm for all tested measurement system combinations. While both were small, the Calypso System RMS error was slightly lower than that of the fluoroscopy when compared against the 4D phantom positions. Of the three trajectories, the RMS error between imaging modalities was largest for the patient trajectory and smallest for the ellipses. Conclusion: This work indicates that both tracking methods provide excellent positioning accuracy. Although the accuracy discrepancy between the two systems is negligible, the Calypso® System also offers the ability to localize in three dimensions and has the advantage of being able to track a target continuously without the use of ionizing radiation.Conflict of Interest: Supported in part by Calypso Medical Technologies, Inc.

Purpose: Common quality assurance procedures for intensity modulated radiotherapy include ionization chamber and/or film measurements in phantom for comparison with point doses and dose distributions predicted by the treatment planning system. We have developed a method to quantitatively compare individual intended fluence maps with measured intensity distributions using an aS500 amorphous silicon electronic portal imager (EPI). Method and Materials: A software program recognizes the intensity map and extracts the intensity in each bixel relative to the maximum bixel value. A simple single‐bixel scatter model was applied to account for scatter in the imager. The software quantitatively compares normalized bixel values in the EPI intensity map with the fluence map exported from the Corvus treatment planning system after correction for scatter. Results: Applying the scatter correction reduces the deviation between EPI maps and planned fluence maps, decreasing the correlation coefficient from 0.59 to 0.24. For 14 gantry angles and a total of 1663 bixels, we compared EPI intensity maps with scatter‐corrected planned fluence maps. The mean error was 1.0% ± 4.1% (1σ) with scatter correction, and 2.4% ± 4.9% (1σ) without scatter correction. Our clinical intensity maps utilize ten intensity levels. When rounded to the nearest intensity level, 69% of all bixels agree with the predicted intensity level, while 99% of bixels are within 10% of the predicted intensity. The majority of bixels in disagreement have low intensity. The mean error for bixels with a planned relative intensity of 10% was 6.3% ± 5.2%. Conclusion: Future refinement of the normalization and scatter correction methods will improve agreement in the low intensity bixels. This would improve the sensitivity of this tool and potentially allow it to replace the more time consuming film and ionization chamber techniques commonly used for IMRTquality assurance.

Intensity modulated radiotherapy(IMRT) provides an improvement in the conformality of radiotherapydose distributions. Its application to photonradiotherapy for prostate adenocarcinoma is well established. A quality assurance tool for verifying photonIMRT treatment and the potential application of intensity modulation to neutronradiotherapy (IMNRT) to prostate cancer are investigated here. This study evaluates the use of an amorphous silicon flat panel imager for dose verification of photonIMRT fields. Various correction factors were developed to allow accurate estimation of the absorbed dose using this portal imager. The ratio of the dose measured with the portal imager to that measured using an ionization chamber was found to be 0.991 ± 0.026 for 23 measured IMRT fields. The study also yielded an accurate estimate of the relative beamlet intensity (fluence) at the plane of the detector. The raw difference between the relative beamlet intensity predicted by the EPID and that of the planning system for 23 IMRT fields was found to be − 0.65 ± 2.69 . These results demonstrate the capabilities of this imager as a robust IMRTquality assurance tool. An in-house optimization algorithm was used to optimize forward planned segments for the treatment of prostate cancer using IMNRT. The applicability of two different algorithms was investigated for IMNRT dose calculation, namely, the differential scatter air ratio (DSAR) and the finite size pencil beam (FSPB) algorithms. Measured profiles and absolute point doses were compared to results calculated by the treatment planning system. Dual ion-chamber measurements were performed to determine the individual neutron and gamma doses and to estimate the whole body dose equivalent. IMNRT plans retrospectively calculated for five prostate cancer patients provided dose distributions superior to conventional fast neutron therapy. When normalized to provide equivalent target coverage, the volume of the rectum and bladder receiving 80% of the prescription dose in the IMNRT plans was reduced by an average of 16% and 13%, respectively. Measured and calculated profiles for IMNRT fields matched to within ± 3 % with the exception of the penumbral region. Absolute point dose measurements also agreed with calculated doses to within ± 3 % at various points within the modulated dose distribution. Whole body dose estimates for IMNRT plans generated in this study were only an average of 16% higher than conventional fast neutron therapy and no significant variations in RBE are expected based on current measurements. Based on the results presented here, clinical implementation of IMNRT is currently achievable.