Perceptions on and roadblocks to implementation of standardized nomenclature in radiation oncology: A survey from TG-263U1.

PURPOSE: AAPM Task Group No. 263U1 (Update to Report No. 263 - Standardizing Nomenclatures in Radiation Oncology) disseminated a survey to receive feedback on utilization, gaps, and means to facilitate further adoption. METHODS: The survey was created by TG-263U1 members to solicit feedback from physicists, dosimetrists, and physicians working in radiation oncology. Questions on the adoption of the TG-263 standard were coupled with demographic information, such as clinical role, place of primary employment (e.g., private hospital, academic center), and size of institution. The survey was emailed to all AAPM, AAMD, and ASTRO members. RESULTS: The survey received 463 responses with 310 completed survey responses used for analysis, of whom most had the clinical role of medical physicist (73%) and the majority were from the United States (83%). There were 83% of respondents who indicated that they believe that having a nomenclature standard is important or very important and 61% had adopted all or portions of TG-263 in their clinics. For those yet to adopt TG-263, the staffing and implementation efforts were the main cause for delaying adoption. Fewer respondents had trouble adopting TG-263 for organs at risk (29%) versus target (44%) nomenclature. Common themes in written feedback were lack of physician support and available resources, especially in vendor systems, to facilitate adoption. CONCLUSIONS: While there is strong support and belief in the benefit of standardized nomenclature, the widespread adoption of TG-263 has been hindered by the effort needed by staff for implementation.  Feedback from the survey is being utilized to drive the focus of the update efforts and create tools to facilitate easier adoption of TG-263.

Results from the AAPM Task Group 324 respiratory motion management in radiation oncology survey.

PURPOSE: To quantify the clinical practice of respiratory motion management in radiation oncology. METHODS: A respiratory motion management survey was designed and conducted based on clinician survey guidelines. The survey was administered to American Association of Physicists in Medicine (AAPM) members on 17 August 2020 and closed on 13 September 2020. RESULTS: A total of 527 respondents completed the entire survey and 651 respondents completed part of the survey, with the partially completed surveys included in the analysis. Overall, 84% of survey respondents used deep inspiration breath hold for left-sided breast cancer. Overall, 83% of respondents perceived respiratory motion management for thoracic and abdominal cancer radiotherapy patients to be either very important or required. Overall, 95% of respondents used respiratory motion management for thoracic and abdominal sites, with 36% of respondents using respiratory motion management for at least 90% of thoracic and abdominal patients. The majority (60%) of respondents used the internal target volume method to treat thoracic and abdominal cancer patients, with 25% using breath hold or abdominal compression and 13% using gating or tracking. CONCLUSIONS: A respiratory motion management survey has been completed by AAPM members. Respiratory motion management is generally considered very important or required and is widely used for breast, thoracic, and abdominal cancer treatments.

Quality and Safety Considerations in Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy: An ASTRO Safety White Paper Update.

PURPOSE: This updated report on stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) is part of a series of consensus-based white papers previously published addressing patient safety. Since the first white papers were published, SRS and SBRT technology and procedures have progressed significantly such that these procedures are now more commonly used. The complexity and submillimeter accuracy, and delivery of a higher dose per fraction requires an emphasis on best practices for technical, dosimetric, and quality assurance. Therefore, quality and patient safety considerations for these techniques remain an important area of focus. METHOD: The American Society for Radiation Oncology convened a task force to assess the original SRS/SBRT white paper and update content where appropriate. Recommendations were created using a consensus-building methodology and task force members indicated their level of agreement based on a 5-point Likert scale, from "strongly agree" to "strongly disagree." A prespecified threshold of ≥75% of raters who select "strongly agree" or "agree" indicated consensus. SUMMARY: This white paper builds on the previous version and uses of other guidance documents to broadly address SRS and SBRT delivery, primarily focusing on processes related to quality and safety. SRS and SBRT require a team-based approach, staffed by appropriately trained and credentialed specialists as well as significant personnel resources, specialized technology, and implementation time. A thorough feasibility analysis of resources is required to achieve the clinical and technical goals and thoroughly discussed with all personnel before undertaking new disease sites. A comprehensive quality assurance program must be developed, using established treatment guidelines, to ensure SRS and SBRT are performed in a safe and effective manner. Patient safety in SRS/SBRT is everyone's responsibility and professional organizations, regulators, vendors, and end-users must demonstrate a clear commitment to working together to ensure the highest levels of safety.

Report of Task Group 201 of the American Association of Physicists in Medicine: Quality management of external beam therapy data transfer.

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.

AAPM Task Group 264: The safe clinical implementation of MLC tracking in radiotherapy.

The era of real-time radiotherapy is upon us. Robotic and gimbaled linac tracking are clinically established technologies with the clinical realization of couch tracking in development. Multileaf collimators (MLCs) are a standard equipment for most cancer radiotherapy systems, and therefore MLC tracking is a potentially widely available technology. MLC tracking has been the subject of theoretical and experimental research for decades and was first implemented for patient treatments in 2013. The AAPM Task Group 264 Safe Clinical Implementation of MLC Tracking in Radiotherapy Report was charged to proactively provide the broader radiation oncology community with (a) clinical implementation guidelines including hardware, software, and clinical indications for use, (b) commissioning and quality assurance recommendations based on early user experience, as well as guidelines on Failure Mode and Effects Analysis, and (c) a discussion of potential future developments. The deliverables from this report include: an explanation of MLC tracking and its historical development; terms and definitions relevant to MLC tracking; the clinical benefit of, clinical experience with and clinical implementation guidelines for MLC tracking; quality assurance guidelines, including example quality assurance worksheets; a clinical decision pathway, future outlook and overall recommendations.

Evaluation of a new secondary dose calculation software for Gamma Knife radiosurgery.

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 < 0.0001. With respect to patients treated at nonstandard gamma angles, the new software was largely independent of patient setup, while the commercial software showed a significant dependence (P-value < 0.0001). The new secondary dose calculation software showed a moderate correlation with calculation depth, while the commercial software showed a weak correlation (Tau = -.322 and Tau = -.217 respectively). Overall, the new secondary software has better agreement with the TPS than the commercially available secondary calculation software over a range of diverse treatment geometries.

Characterization and validation of an intra-fraction motion management system for masked-based radiosurgery.

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 <0.1 mm. The measured latency was <200 ms. The dose difference with five interruptions was <0.5%. CONCLUSION: This work provides a quantitative characterization of the GKI IFMM system as required by the Nuclear Regulatory Commission. This provides a methodology for GKI users to satisfy these requirements using common laboratory equipment in lieu of a commercial solution.

First clinical implementation of real-time, real anatomy tracking and radiation beam control.

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.

American Association of Physicists in Medicine Task Group 263: Standardizing Nomenclatures in Radiation Oncology.

A substantial barrier to the single- and multi-institutional aggregation of data to supporting clinical trials, practice quality improvement efforts, and development of big data analytics resource systems is the lack of standardized nomenclatures for expressing dosimetric data. To address this issue, the American Association of Physicists in Medicine (AAPM) Task Group 263 was charged with providing nomenclature guidelines and values in radiation oncology for use in clinical trials, data-pooling initiatives, population-based studies, and routine clinical care by standardizing: (1) structure names across image processing and treatment planning system platforms; (2) nomenclature for dosimetric data (eg, dose-volume histogram [DVH]-based metrics); (3) templates for clinical trial groups and users of an initial subset of software platforms to facilitate adoption of the standards; (4) formalism for nomenclature schema, which can accommodate the addition of other structures defined in the future. A multisociety, multidisciplinary, multinational group of 57 members representing stake holders ranging from large academic centers to community clinics and vendors was assembled, including physicists, physicians, dosimetrists, and vendors. The stakeholder groups represented in the membership included the AAPM, American Society for Radiation Oncology (ASTRO), NRG Oncology, European Society for Radiation Oncology (ESTRO), Radiation Therapy Oncology Group (RTOG), Children's Oncology Group (COG), Integrating Healthcare Enterprise in Radiation Oncology (IHE-RO), and Digital Imaging and Communications in Medicine working group (DICOM WG); A nomenclature system for target and organ at risk volumes and DVH nomenclature was developed and piloted to demonstrate viability across a range of clinics and within the framework of clinical trials. The final report was approved by AAPM in October 2017. The approval process included review by 8 AAPM committees, with additional review by ASTRO, European Society for Radiation Oncology (ESTRO), and American Association of Medical Dosimetrists (AAMD). This Executive Summary of the report highlights the key recommendations for clinical practice, research, and trials.

Completion of Gamma Knife radiosurgery for AVM treatment after unplanned interruption-technical note.

BACKGROUND AND IMPORTANCE: Gamma Knife radiosurgery is an established technique for non-urgent treatment of various intracranial pathologies. Intra-procedural dislodgement of the stereotactic frame is an uncommon occurrence that could lead to abortion of ongoing treatment and necessitate more invasive treatment strategies. CLINICAL PRESENTATION: In this case report, we describe a novel method for resumption of Gamma Knife treatment after an unplanned intra-procedural interruption. The case example involves a radiosurgical treatment of a Spetzler-Martin grade I arteriovenous malformation. CONCLUSION: Our technique involves integration of scans and coordinate systems from two imaging sessions using the composite isodose line to resolve translational differences, thereby limiting delivery of remaining shots to the untreated region of the lesion. MRI follow-up at 13 months showed a reduction in the nidus size with no evidence of any radiation injury to the surrounding brain parenchyma. We believe this technique will allow care teams to effectively salvage interrupted Gamma Knife procedures and reduce progression to more invasive treatment options.

Common error pathways seen in the RO-ILS data that demonstrate opportunities for improving treatment safety.

PURPOSE: The Radiation Oncology Incident Learning System (RO-ILS) receives event reports from facilities across the country. This effort extracted common error pathways seen in the data. These pathways, expressed as fault trees, demonstrate the need for, and opportunities for, preventing these errors and/or limiting their propagation to treatment. METHODS AND MATERIALS: As of the third quarter of 2016, 2344 event reports had been submitted to RO-ILS and reviewed. A total of 396 of the reports judged highest priority were rereviewed and assigned up to 3 keywords to classify events. Based on patterns among the keyword assignments, the data were further aggregated into pathways leading to 3 general error types: "problematic plan approved for treatment," "wrong shift instructions given to therapists," and "wrong shift performed at treatment." Fault trees were created showing how different errors at different stages in the treatment process combine to flow into these general error types. RESULTS: A total of 173 of the 396 (44%) events were characterized as belonging to 1 of these 3 general error types. Ninety-nine events were defined as "problematic plan approved for treatment," 40 as "wrong shift instructions given to therapists," and 34 as "wrong shift performed at treatment." Seventy-six of these events (44%) resulted in incorrectly delivered treatment. Event discovery was by therapists (n = 76), physicists (n = 45), physicians (n = 23), dosimetrists (n = 15), or not identified (n = 9); 5 events were found as a result of the patient questioning the staff. For the event type "problematic plan approved for treatment," 64 of the 99 (65%) events were attributable to physician error: incorrect target or dosing pattern prescribed. CONCLUSIONS: Data extracted from RO-ILS event reports demonstrate common error pathways in radiation oncology that propagate all the way to treatment. Additional study and coordination of efforts is needed to develop and share best practices to address the sources of these errors and curtail their propagation.

Two-and-a-half-year clinical experience with the world's first magnetic resonance image guided radiation therapy system.

PURPOSE: Magnetic resonance image guided radiation therapy (MR-IGRT) has been used at our institution since 2014. We report on more than 2 years of clinical experience in treating patients with the world's first MR-IGRT system. METHODS AND MATERIALS: A clinical service was opened for MR-IGRT in January 2014 with an MR-IGRT system consisting of a split 0.35T magnetic resonance scanner that straddles a ring gantry with 3 multileaf collimator-equipped 60Co heads. The service was expanded to include online adaptive radiation therapy (ART) MR-IGRT and cine gating after 6 and 9 months, respectively. Patients selected for MR-IGRT were enrolled in a prospective registry between January 2014 and June 2016. Patients were treated with a variety of radiation therapy techniques including intensity modulated radiation therapy and stereotactic body radiation therapy (SBRT). When applicable, online ART was performed and gating on sagittal 2-dimensional cine MR was used. The charts of patients treated with MR-IGRT were reviewed to report on the clinical and treatment characteristics of the initial patients who were treated with this novel technique. RESULTS: A total of 316 patients have been treated with the MR-IGRT system, which has been integrated into a high-volume clinic. The cases were most commonly selected for improved soft tissue visualization, ART, and cine gating. Seventy-six patients were treated with 3-dimensional conformal radiation therapy, 146 patients with intensity modulated radiation therapy, and 94 patients with SBRT. The most commonly treated disease sites were the abdomen (28%), breast (26%), pelvis (22%), thorax (19%), and head and neck (5%). Sixty-seven patients were treated with online ART over a total of 244 adapted fractions. Cine treatment gating was used for a total of 81 patients. CONCLUSIONS: MR-IGRT has been successfully implemented in a high-volume radiation clinic and provides unique advantages in the treatment of a variety of malignancies. Additional clinical trials are in development to formally evaluate MR-IGRT in the treatment of multiple disease sites with techniques such as SBRT and ART.

Rapid acceptance testing of modern linac using on-board MV and kV imaging systems.

PURPOSE: The purpose of this study was to develop a novel process for using on-board MV and kV Electronic Portal Imaging Devices (EPIDs) to perform linac acceptance testing (AT) for two reasons: (a) to standardize the assessment of new equipment performance, and (b) to reduce the time to clinical use while reducing physicist workload. METHODS AND MATERIALS: In this study, Varian TrueBeam linacs equipped with amorphous silicon-based EPID (aS1000) were used. The conventional set of AT tests and tolerances were used as a baseline guide. A novel methodology was developed or adopted from published literature to perform as many tests as possible using the MV and kV EPIDs. The developer mode on Varian TrueBeam linacs was used to automate the process. In the EPID-based approach, most of mechanical tests were conducted by acquiring images through a custom phantom and software tools were developed for quantitative analysis to extract different performance parameters. The embedded steel-spheres in a custom phantom provided both visual and radiographic guidance for beam geometry testing. For photon beams, open field EPID images were used to extract inline/crossline profiles to verify the beam energy, flatness and symmetry. EPID images through a double wedge phantom were used for evaluating electron beam properties via diagonal profile. Testing was augmented with a commercial automated application (Machine Performance Check) which was used to perform several geometric accuracy tests such as gantry, collimator rotations, and couch rotations/translations. RESULTS: The developed process demonstrated that the tests, which required customer demonstration, were efficiently performed using EPIDs. The AT tests that were performed using EPIDs were fully automated using the developer mode on the Varian TrueBeam system, while some tests, such as the light field versus radiation field congruence, and collision interlock checks required user interaction. CONCLUSIONS: On-board imagers are quite suitable for both geometric and dosimetric testing of linac system involved in AT. Electronic format of the acquired data lends itself to benchmarking, transparency, as well as longitudinal use of AT data. While the tests were performed on a specific model of a linear accelerator, the proposed approach can be extended to other linacs.

Technical Note: Magnetic field effects on Gafchromic-film response in MR-IGRT.

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.

Commissioning and initial experience with the first clinical gantry-mounted proton therapy system.

The purpose of this study is to describe the comprehensive commissioning process and initial clinical experience of the Mevion S250 proton therapy system, a gantry-mounted, single-room proton therapy platform clinically implemented in the S. Lee Kling Proton Therapy Center at Barnes-Jewish Hospital in St. Louis, MO, USA. The Mevion S250 system integrates a compact synchrocyclotron with a C-inner gantry, an image guidance system and a 6D robotic couch into a beam delivery platform. We present our commissioning process and initial clinical experience, including i) CT calibration; ii) beam data acquisition and machine characteristics; iii) dosimetric commissioning of the treatment planning system; iv) validation through the Imaging and Radiation Oncology Core credentialing process, including irradiations on the spine, prostate, brain, and lung phantoms; v) evaluation of localization accuracy of the image guidance system; and vi) initial clinical experience. Clinically, the system operates well and has provided an excellent platform for the treatment of diseases with protons.

Cone-Beam Computed Tomography Internal Motion Tracking Should Be Used to Validate 4-Dimensional Computed Tomography for Abdominal Radiation Therapy Patients.

PURPOSE: To demonstrate that fiducial tracking during pretreatment Cone-Beam CT (CBCT) can accurately measure tumor motion and that this method should be used to validate 4-dimensional CT (4DCT) margins before each treatment fraction. METHODS AND MATERIALS: For 31 patients with abdominal tumors and implanted fiducial markers, tumor motion was measured daily with CBCT and fluoroscopy for 202 treatment fractions. Fiducial tracking and maximum-likelihood algorithms extracted 3-dimensional fiducial trajectories from CBCT projections. The daily internal margin (IM) (ie, range of fiducial motion) was calculated for CBCT and fluoroscopy as the 5th-95th percentiles of displacement in each cardinal direction. The planning IM from simulation 4DCT (IM4DCT) was considered adequate when within ±1.2 mm (anterior-posterior, left-right) and ±3 mm (superior-inferior) of the daily measured IM. We validated CBCT fiducial tracking as an accurate predictive measure of intrafraction motion by comparing the daily measured IMCBCT with the daily IM measured by pretreatment fluoroscopy (IMpre-fluoro); these were compared with pre- and posttreatment fluoroscopy (IMfluoro) to identify those patients who could benefit from imaging during treatment. RESULTS: Four-dimensional CT could not accurately predict intrafractional tumor motion for ≥80% of fractions in 94% (IMCBCT), 97% (IMpre-fluoro), and 100% (IMfluoro) of patients. The IMCBCT was significantly closer to IMpre-fluoro than IM4DCT (P<.01). For patients with median treatment time t < 7.5 minutes, IMCBCT was in agreement with IMfluoro for 93% of fractions (superior-inferior), compared with 63% for the t > 7.5 minutes group, demonstrating the need for patient-specific intratreatment imaging. CONCLUSIONS: Tumor motion determined from 4DCT simulation does not accurately predict the daily motion observed on CBCT or fluoroscopy. Cone-beam CT could replace fluoroscopy for pretreatment verification of simulation IM4DCT, reducing patient setup time and imaging dose. Patients with treatment time t > 7.5 minutes could benefit from the addition of intratreatment imaging.

Characterization of the onboard imaging unit for the first clinical magnetic resonance image guided radiation therapy system.

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(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 resolved 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.