Purpose/Objective(s) Men with Grade Group 2 (GG2) intermediate risk (IR) prostate cancer (PCa) have multiple curative radiation (RT) options. Compared to conventional external beam photon RT (XRT), including 3D-conformal RT (3DCRT) and IMRT, highly conformal RT techniques may provide less integral RT dose to normal tissue, including brachytherapy (BT), SBRT, and proton beam radiation therapy (PBT). These treatments require either advanced equipment and/or specialized training. Here we analyzed national trends in utilization of XRT, BT monotherapy, SBRT, and PBT, and assessed potential factors associated with receiving each technique. We hypothesize that socioeconomic and/or racial disparities are associated with differences in utilization of these specialized techniques. Materials/Methods Men diagnosed with favorable IR PCa cancer, defined as Gleason 3+4 disease, PSA < 20 and clinical stage T1-T2 N0 M0, between 2004-2017 were identified in the National Cancer Database. Cohorts were defined as: XRT (3DCRT+IMRT, hypofractionated (HF) or standard fractionation (SF)), BT monotherapy (HDR, LDR), SBRT (5 fx) and PBT (HF or SF). Trends in utilization were examined. Associations between technique and patient, clinical disease, and sociodemographic characteristics were assessed by multivariable logistic regression, with P<0.05 considered significant. Results 71,140 patients met inclusion criteria of which 72.4% received standard XRT and 27.6 % received specialized radiation modalities (18.5% brachytherapy, 6.0% SBRT, & 3.1% PBT). Utilization of XRT and BT declined from 71.0% (XRT) and 27.5% (BT) in 2004 to 69.7% (XRT) and 17.2% (BT) in 2017. Receipt of SBRT and PBT increased from 0% (SBRT) and 1.45% (PBT) in 2004 to 9.9% (SBRT) and 3.3% (PBT) in 2017, respectively. On multivariable logistic regression, Black patients were less likely to receive BT (adjusted OR 0.79; 95%CI 0.74-0.83), SBRT (adjusted OR 0.77; 95%CI 0.70-0.85), or PBT (adjusted OR 0.39; 95%CI 0.33-0.47) compared to XRT (all P<0.0001). Socially disadvantaged seniors (SDS; age >65 years with Medicaid insurance) were less likely to receive specialized RT (adjusted OR 0.45; 95%CI 0.31-0.60; P<0.0001). Factors associated with increased likelihood of receiving BT, SBRT, or PBT included: treatment at Academic/Research center, treatment at a metropolitan facility, younger age, lower Charlson-Deyo Comorbidity Score, and lower PSA at presentation (all P < 0.01). Conclusion Trends in utilization of RT modalities have dramatically changed in recent years with a sharp decline in BT, a doubling of PBT, and rapid adoption of SBRT, as coded in the NCDB. Compared to White patients with GG2 IR PCa, there are disparities in utilization of BT, SBRT, and PBT for Black patients and for SDS. It is unclear whether similar disparities exist for other prostate cancer grade groups for which BT and SBRT are being utilized. Future efforts should address access-to-care challenges for the use of these specialized techniques as they are expanded into higher GG.

PURPOSE:The current approach to Linac beam dosimetry verification is typically performed utilizing a three-dimensional (3D) water tank system. The 3D beam scanning process is cumbersome, labor intensive, error-prone, and costly. This is especially challenging for the new Ethos system and MR Linacs with a ring gantry. This work proposes an alternative approach to verify 6FFF beam dosimetry for Ethos, ViewRay MRIdian® Linac, and other Linacs with 6FFF beam quality using two-dimensional (2D) ion chamber arrays.METHODS:Percentage depth dose (PDD) and profiles of an Ethos, an MRIdian® Linac, and several Linacs with 6FFF beams were measured at the nominal beam current. The beam energy was detuned by changing the bending magnet current on one TrueBeam. PDDs and profiles were measured for detuned beam energies. The peak shape of the 6FFF profile was defined by a "slope" parameter and unflatness. Correlations between peak slope and unflatness metrics vs PDDs were used to evaluate the sensitivity of beam energy to beam profile changes at different field sizes and depths.RESULTS:Strong correlations were found between peak slope and PDDs for all Linacs with 6FFF beam. The R-squared values in the linear regression fitting between PDD and peak slope and unflatness were 0.99 and 0.84, respectively. Both profile slope and unflatness were proportional to PDD at the 10 cm depth and the peak slope was 4.3 times more sensitive than PDD. We have identified that measurements with a shallow depth are preferred to quantify the beam energy consistency.CONCLUSIONS:Our work shows the feasibility of verifying 6FFF beam quality of Ethos, MR Linac, and other Linacs by defining a profile slope measured from 2D ionization chambers array devices. This new approach provides a simplified method for performing a routine beam quality check without using a 3D water tank system while maximizing cost effectiveness and efficiency.

The Coronavirus 2019 (COVID-19) pandemic has severely impacted healthcare systems by putting a massive strain on emergency, intensive care, internal medicine departments, and caregivers. Outpatient care, including radiation oncology, has also been disrupted, forcing departments to modify operations so that patients can continue to obtain treatment in the safest and most effective manner possible. This can be challenging to implement while balancing the goals of continuing to provide high-quality treatment, complete large-scale projects, and increase access to care in the community. Throughout this pandemic, our department has adjusted operations by leveraging technology and our diverse skills to ensure that high-quality patient care could be given while minimizing potential COVID-19 exposures to patients and staff. During this process, we have learned a great deal from our experience. The goal of this work is to share these lessons so they may be translated across a wide range of medical physics practices. Our physics group is organized around six main core values: patient care, integrity, teamwork, community, advancement, and us. These core values help steer the goals of our physics group across all three major branches of service: Clinical, Research, and Education. Our radiation oncology department spans 10 locations, including a large main academic center and nine community-based practices that range in size from small (single linac) to mid-size (up to three linacs and brachytherapy). The department as a whole treats approximately 450-550 patients per day with 100 to 200 patient plans in the planning process. Enterprise services include brachytherapy, external beam therapy, adaptive radiation therapy, quality assurance (QA), proton therapy, treatment planning, stereotactic body radiotherapy, (SBRT), stereotactic radiosurgery (SRS), and satellite operations covered by a team of nearly 40 physicists. The locations of these satellites surround the metro area with three regional satellite locations within a 3-hour drive. Most of the specialty services (e.g. protons, adaptive) are situated at the main campus, otherwise, the local satellites sites are all integrated into a single, shared external beam service, while the three regional satellites operate largely independently. This structure was designed several years ago to cover all the clinical needs, allow for flexibility in scheduling by having many interchangeable team members. This flexibility is very helpful to ensure robust coverage from week to week; however, it is easy to see this level of mobility could pose a severe risk to the spread of infection between services and locations, as a single physicist could potentially spread the virus very quickly across nearly every location and service. After the first reports of COVID-19 in the United States, it became clear that our traditional staffing structure had inherent risk and needed modification to minimize interaction and transmission of any infection among staff. If a single physicist could travel between up to five sites in a single week, there was an increased risk of virus transmission between sites. Immediate action was taken to minimize this, with the goal of still maintaining the full range of physics operations needed. A transmission minimization scheme was quickly created and deployed the first week the threat of COVID-19 in the United States became clear. Physicists were organized into groups, or "pods", to cover the different services and locations. All physicists were assigned to a single location and instructed to either work at that location ("on-site") or remote work from home ("off-site"). Each satellite was assigned at least two physicists who alternated coverage on a weekly basis: 1 week on-site and 1 week off-site (remote work from home) without overlapping with their partners. At the main campus, each service was treated largely as separate entities to avoid cross-pod interactions. On-site assignments were completed on a weekly basis and then rotated to off-site (home) for at least 1 week. Staffing was limited to only when physically needed in each area, and all other physicists were moved to remote work from home. While working from home, each physicist was expected to remotely apply their particular expertise wherever needed during the day. If a physicist needed to change sites due to a staffing need, a weeklong off-site coverage was utilized as a buffer when switching between sites. Initially, academic time was limited to only grant-funded personnel, with all department funded research efforts being temporarily put on hold to better support clinical efforts. This allowed time to carefully assess the pandemic while putting clinical operations at the forefront, and then focus on bringing back education and research operations as deemed safe. All physicists that were deemed by their physician to be medically at high risk for complications of COVID-19 were granted an accommodation and worked from home exclusively. The entire dosimetry team was moved to remote work from home. These policy changes coincided with the announcement of stay at home orders in the metro area on March 23, 2020, along with the School of Medicine hold on travel outside of a 60-mile radius of campus issued on March 18, 2020. To comply with this order, all vacation requests were temporarily revoked and faculty time off was handled on a case-by-case basis. All physicists working on-site were provided with personal protective equipment (PPE) deemed necessary per hospital policy. All physicists were instructed to practice social distancing, proper hand hygiene, and work area sanitation while on-site. Employee and patient pre-screening and mandatory face mask use were implemented across all facilities. To ensure effective communication and coordination of duties under the "pod" and remote work model, a standing 7 am daily COVID-19 remote huddle was established on March 16, 2020 between the different leaders of the department consisting of the radiation oncology department chair, radiation oncology clinical director, hospital director of radiation oncology, medical physics director, chief of clinical medical physics, department director of business operations, and director of business affairs. Daily remote physics huddles were established to quickly adapt to the ever-changing situation and disseminate information across all the clinical teams. As the pandemic continued and operations stabilized, daily huddles became weekly, and then as needed based on metro area case load surge and hospital operations. Faculty academic time and educational activities resumed as soon as possible with changes in our standard operating procedures, for example moving teaching to remote classes. Overall, this resulted in a return to a consistent clinical staffing level (i.e., in terms of full-time equivalent effort) as pre-pandemic. Areas where we historically thought only on-site support could occur can now be supported remotely as well as onsite.1, 2 For instance, one Gamma Knife physicist is on site per our NRC requirements but we can also have a second physicist logged in via remote network keyboard video mouse (IP-KVM) access and communicating via video conference to provide additional coverage that, pre-pandemic, would have been on-site only. Similarly, in brachytherapy, we can supplement on-site coverage with remote plan checks. Major projects such as commissioning of a linear accelerator, commissioning of a proton accelerator, and taking on a new regional satellite location were also completed during the pandemic. These were only possible by ensuring our staff stayed safe and healthy and our clinical coverage remained intact. Our staffing model and department culture helped to ensure the success of these challenging projects. Staffing and staff safety is obviously a challenge one could face during the pandemic. Even with the best preparations, it is very likely staffing will be affected by direct infection, quarantine due to exposure, or existence of any symptoms identified in the daily screening. Furthermore, these issues are extended to the staff's family. For example, if a daycare is closed with little notice due to a COVID-19 exposure and there is no back up childcare option, this can cause major issues in clinical coverage if a parent must take over child care and become unavailable for clinical duty. These unplanned changes in clinical coverage often need to be addressed and communicated out to the team quickly and concisely. This can be challenging and stressful to deal with if there is no built-in redundancy and backup system in the staffing model. Developing a clear and robust strategy to back fill these unscheduled absences is vital, and without a strong culture of teamwork this can be an immense challenge. Each pod was designed to consist of at least one on-site physicist and a partner who is rotated off-site; therefore, a logical first backup is the off-site physicist with redundant backup coverage from other services second. Adapting to ever-changing and uncertain conditions can be extremely frustrating and stressful. When the pandemic started there were many unanswered questions. A year later, some of these have been addressed but many more continue to emerge with regularity. As we learn new information and the action plan changes, effective team communication is crucial, including both dissemination of information from leadership to the team, and within the rest of the group. Keeping in mind these challenges, it is important to deal with the stress and anxiety that can come along with this uncertain and ever-changing environment. Without strong communication and support from leadership and within the team, this challenge can often feel overwhelming. A morning physics huddle has been a very useful forum to not only share information with the group, but also to get feedback, allow staff to alert leadership to problems, and enable group discussion and consensus on challenging issues. These video calls can help provide a more personal connection and support for each other while safely social distancing. A strong work culture has been instrumental in keeping our physics team functioning at a high level in the face of these immense challenges. This has not been easy, but the culture built around our core values is more important than the technology and strategies we have adopted during the pandemic. Our biggest piece of advice to any physics group is to build a strong culture by defining and embracing the core values, that are important to the team, and that will serve as the foundation to rest on. Effectively designing a remote work from home program was critical to the success of the "pod" model of staffing we implemented, as it helped manage on-site staffing while providing flexibility in coverage. Crucially, this involved a remote work from home rotation in small teams, ensuring each physicist spent a week of time on-site every 2 weeks. It is important to remember physicists do much more than QA and checking charts. Physicists are crucial care team members helping to ensure the clinic runs smoothly and safely. Physicists often help coordinate the process and communication amongst the multiple different team members (physicists, physicians, therapists, dosimetrists, etc.) for complicated cases and special procedures. These interactions are extremely valuable to building safe and effective radiation therapy programs. Thus, a remote work from home program for physicists must be carefully designed to ensure physicists are available and present in the clinical environment. For example, naively scheduling all chart check work to be remote and procedural work to be on site would likely result in a similar coverage risk as standard operations, would degrade the team culture, and would likely result in inferior quality. Employing the pod-based rotation between on-site versus remote work has largely been a great success to supplement on-site coverage while reducing the exposure risk without forcing pure isolation on individuals in the team. The team has embraced numerous remote meeting and communication technologies to bridge the team's physical gap. Leadership supported funds and technology to provide staff with effective remote computing and office tools while providing the necessary resources to ensure that crucial on-site physics support can continue safely. To date, not a single case has been cancelled due to a lack of physics availability. Certainly, the pandemic has been challenging for everyone, including our team, both professionally and personally. However, it has also brought the team together to step up to the challenge, strengthening our core values, and cementing our culture. Distributing the clinical workload across a larger group consisting of both on site and remote physicists while building in redundancy, and emphasizing a culture of teamwork, were all key components to our success in maintaining physics operations in the pandemic. Working together to support the entire team allowed us to not only sustain clinical operations but also complete major projects. The structure of the coverage pods ensures if there is an exposure, it is limited within a relatively small group and not across multiple sites. The pod members are isolated from the rest of the coverage teams, who could then rotate to fill this gap while the exposed group recovers. An exposed pod member also has a "built-in" minimum quarantine of 5 days due to the week-on-week-off model of coverage. This can easily be extended quickly if the need arises. This structure of working a week on-site and then a week off-site numerous times limited the impact of unplanned staffing issues that arose on clinical operations. It is important to note that in addition to social distancing, we implemented "expertise distancing", meaning the expertise holders remained on separate pods but were still able to effectively share their expertise for an assigned service. For instance, the brachytherapy physics service chief was not scheduled together with the assistant service chief if possible. This was designed to minimize the risk of both being out simultaneously and therefore limiting the available brachytherapy physics resources. Similarly, for staff at our single physicist centers, we paired them with multiple backup physicists who could provide remote support as well as on-site assistance if the need arose. This is obviously much easier for a large physics group to provide than a solo physicist working independently, but the current pandemic exposes the need for emergency backup coverage. As a group we have been extremely fortunate to have access to the COVID-19 vaccine. Even though operations are not likely to return to the pre-pandemic state soon, we are hopeful things will continue to improve over the coming months. From this experience, we see physics groups can continue to be effective in delivering high-quality and timely patient care while minimizing the risk of virus transmission to staff or patients across a diverse spectrum of radiation oncology practices. The challenges a department of our size faced are no doubt unique, but the actions taken are scalable and can be directly translated to any radiation oncology department. The lessons learned handling a global pandemic can help us and other centers respond effectively to similar emergency situations. The year of 2020 was a very difficult year, and the only way we were able to be successful was with strong support from our department leadership including: our department head Dr. Dennis Hallahan, business office leadership Dan Kinzel and Lisa DeBerry, director of radiation oncology at Barnes Jewish Hospital Sharon Endicott, and our clinical director Dr. Jeff Michalski. The mentorship and guidance from our former director of physics Dr. Sasa Mutic was crucial at the beginning of the pandemic. Finally, we would like to thank all our colleagues in radiation oncology particularly the clinical and support staff in our department. It has been a privilege to work with this group throughout this very challenging time. We thank Deputy Editors-in-Chief Timothy Solberg and Per Halvorsen for their valuable and perceptive comments.

Adaptive radiotherapy (ART) is a specialized, multi-step process requiring substantial physician time and expertise to satisfactorily treat patients. Implementing specialized technologies is difficult due to the time commitment and unique physician expertise required for successful completion of treatment. As use of ART increases, the ability to provide tele-ART may ease workflow burdens and improve overall patient access to specialty care within an institutional, regional, or broader network. To address this need, we designed and piloted a novel tele-ART system in a multi-satellite academic network. We hypothesized that multiple potential failure modes would exist within the tele-ART system and conducted a risk analysis to identify potential failures prior to deploying tele-ART for routine clinical care. The institutional tele-ART system includes a commercial grade frame-grabber capturing up to 1900x1200 at 60fps, to connect the treatment delivery system (TDS) to a secondary computer. The treatment team including physics then video calls the covering radiation oncologist (RO) via a HIPAA compliant commercial collaboration platform (CP), which shares the captured frames from the secondary computer. Evaluation of image registration metrics between the TDS screen and RO's shared screen was performed via cross-correlation, as was lag time through the CP. The RO can control the view-only secondary screen and communicate with the team through the audio of the video call, thus providing remote image and ART plan review in real time. Failure modes of this process were evaluated by FMEA analysis. Specifically, a process map was created assuming the RO is absent from the machine but available within the department or in-network satellites. FMEA scoring utilizing a risk priority number (RPN) process was individually completed by 2 physicists, 2 therapists, and 3 ROs, all experienced in ART. The cross correlation between the TDS screen and the RO shared screen was 0.96. The lag in the CP video sharing was 0.05s. 129 failure modes (FM) were identified in our process map. Multiple repeat FM were identified at different steps of the process. The FM most often scored in the top 20% of RPN scores was RO distraction during multiple ART workflow steps due to the possibility of an RO being in the midst of a competing task. Other FMs with RPNs in the top 20% included misinterpretation of data or missed data due to system lag or changes in visual/audio quality. A novel method to perform view-only tele-ART has been created at our institution. FMEA analysis successfully identified several high-risk aspects of a tele-ART system. Quality measures are now underway to address these failure modes prior to routine clinical implementation of this service, which is a first step in providing highly specialized ART treatment to the broader radiation oncology community.

Magnetic resonance (MR) image (MRI) guided radiation therapy (MRgRT) confers superior daily soft-tissue target visualization for many anatomic sites compared with traditional computed tomography (CT)–based radiation therapy and is increasingly used to manage inter- and intrafraction motion in a variety of cancer diagnoses.1,2 There is growing evidence that MRgRT may be used to improve the dosimetric therapeutic index of radiation treatment through improved daily setup accuracy, the opportunity for daily online plan adaptation, and real-time cine MRI tumor motion tracking with beam gating.

Purpose The superior soft-tissue contrast achieved using magnetic resonance imaging (MRI) compared to x-ray computed tomography (CT) has led to the popularization of MRI-guided radiation therapy (MR-IGRT), especially in recent years with the advent of first and second generation MRI-based therapy delivery systems for MR-IGRT. The expanding use of these systems is driving interest in MRI-only RT workflows in which MRI is the sole imaging modality used for treatment planning and dose calculations. To enable such a workflow, synthetic CT (sCT) data must be generated based on a patient's MRI data so that dose calculations may be performed using the electron density information derived from CT images. In this study, we propose a novel deep spatial pyramid convolutional framework for the MRI-to-CT image-to-image translation task and compare its performance to the well established U-Net architecture in a generative adversarial network (GAN) framework. Methods Our proposed framework utilizes atrous convolution in a method named atrous spatial pyramid pooling (ASPP) to significantly reduce the total number of parameters required to describe the model while effectively capturing rich, multi-scale structural information in a manner that is not possible in the conventional framework. The proposed framework consists of a generative model composed of stacked encoders and decoders separated by the ASPP module, where atrous convolution is applied at increasing rates in parallel to encode large-scale features. The performance of the proposed method is compared to that of the conventional GAN framework in terms of the time required to train the model and the image quality of the generated sCT as measured by the root mean square error (RMSE), structural similarity index (SSIM), and peak signal-to-noise ratio (PSNR) depending on the size of the training data set. Dose calculations based on sCT data generated using the proposed architecture are also compared to clinical plans to evaluate the dosimetric accuracy of the method. Results Significant reductions in training time and improvements in image quality are observed at every training data set size when the proposed framework is adopted instead of the conventional framework. Over 1042 test images, values of 17.7 +/- 4.3 HU, 0.9995 +/- 0.0003, and 71.7 +/- 2.3 are observed for the RMSE, SSIM, and PSNR metrics, respectively. Dose distributions calculated based on sCT data generated using the proposed framework demonstrate passing rates equal to or greater than 98% using the 3D gamma index with a 2%/2 mm criterion. Conclusions The deep spatial pyramid convolutional framework proposed here demonstrates improved performance compared to the conventional GAN framework that has been applied to the image-to-image translation task of sCT generation. Adopting the method is a first step toward an MRI-only RT workflow that enables widespread clinical applications for MR-IGRT including online adaptive therapy.

Purpose or ObjectiveIntensity-modulated proton therapy (IMPT) is very sensitive to small daily density variations along the pencil beam paths and variations in target and OAR shapes.This makes IMPT for sites with large inter-fraction target

The fast evolution of technology in radiotherapy (RT) enabled the realization of adaptive radiotherapy (ART). However, the new characteristics of ART pose unique challenges for efficiencies and effectiveness of quality assurance (QA) strategies. In this paper, we discuss the necessary QAs for ART and introduce a practical implementation. A previously published work on failure modes and effects analysis (FMEA) of ART is introduced first to explain the risks associated with ART sub-processes. After a brief discussion of QA challenges, we review the existing QA strategies and tools that might be suitable for each ART step. By introducing the MR-guided online ART QA processes developed at our institute, we demonstrate a practical implementation. The limitations and future works to develop more robust and efficient QA strategies are discussed at the end.

To simplify the adaptive treatment planning workflow while achieving the optimal tumor-dose coverage in pancreatic cancer patients undergoing daily adaptive magnetic resonance image guided radiation therapy (MR-IGRT).

PURPOSE:Episcleral plaque brachytherapy (EPB) planning is conventionally based on approximations of the implant geometry with no volumetric imaging following plaque implantation. We have developed an MRI-based technique for EPB treatment planning and dose delivery verification based on the actual patient-specific geometry. METHODS AND MATERIALS:MR images of 6 patients, prescribed 85 Gy over 96 hours from Collaborative Ocular Melanoma Study-based EPB, were acquired before and after implantation. Preimplant and postimplant scans were used to generate "preplans" and "postplans", respectively. In the preplans, a digital plaque model was positioned relative to the tumor, sclera, and nerve. In the postplans, the same plaque model was positioned based on the imaged plaque. Plaque position, point doses, percentage of tumor volume receiving 85 Gy (V100), and dose to 100% of tumor volume (Dmin) were compared between preplans and postplans. All isodose plans were computed using TG-43 formalism with no heterogeneity corrections. RESULTS:Shifts and tilts of the plaque ranged from 1.4 to 8.6 mm and 1.0 to 3.8 mm, respectively. V100 was ≥97% for 4 patients. Dmin for preplans and postplans ranged from 83 to 118 Gy and 45 to 110 Gy, respectively. Point doses for tumor apex and base were all found to decrease from the preimplant to the postimplant plan, with mean differences of 16.7 ± 8.6% and 30.5 ± 11.3%, respectively. CONCLUSIONS:By implementing MRI for EPB, we eliminate reliance on approximations of the eye and tumor shape and the assumption of idealized plaque placement. With MRI, one can perform preimplant as well as postimplant imaging, facilitating EPB treatment planning based on the actual patient-specific geometry and dose-delivery verification based on the imaged plaque position.

To provide quality radiation oncology service and patient care, a better understanding of the error reporting system and culture in radiotherapy facilities is vital in each step of the treatment process. Obstacles to reporting must be identified in order to provide awareness into potential areas for improvement. This study conducted a survey of radiotherapy staff to examine the error reporting cultures in a radiation oncology facility, as well as, staff comfort in reporting errors. This study conducted a survey on 38 personnel of the Department of Radiotherapy, Jose R. Reyes Memorial Medical Center, Manila, Philippines. The survey focused on overall communication between different professions in radiotherapy, awareness and comfort level on treatment error reporting, and obstacles on treatment error reporting. The survey results were analyzed using descriptive methods. A 74% of the staff are aware that there is an existing treatment error reporting system in the facility. All respondents agreed that the adaptation of the ASTRO framework on error reporting (adapted last 2016) is appropriate in their setup. The adaptation of the said framework has lead to a comprehensive reporting of the errors based on the following factors: stages on radiotherapy of process, direct causes and contributing factors leading to treatment errors. Based on the data of the department for the year 2016, each of the above factors were analyzed. The top stages of the RT process with the highest reported errors are during the treatment delivery (51%). Moreover, the top direct cause of treatment errors are incorrect data recorded (23%), while the top contributing factor to treatment errors are inattention to details (49%). The survey showed that majority have good personal overall communications with the other staff of the department ranging from 50% (administrators) to 84% (physicians). Also, the results showed a good overall interdisciplinary communication within the department staff ranging from 47% (medical physicists-administrators) to 74% (medical physicists-physicians). About 68% and 58% of the respondents are encouraged and comfortable to report errors, respectively. The top 3 obstacles to reporting errors are: fear of reprimand (42%), poor communication (34%), and lack of reporting system (26%). Although the system does not promote blaming, 16% of the respondents perceived that they have been personally reprimanded due to an error. The adaptation of the ASTRO framework on reporting errors resulted in better identification of areas and factors for improvement Majority of the interpersonal and interdisciplinary communications in the facility is good. Most of the personnel are encouraged and comfortable in reporting treatment errors, although, the top obstacles to error reporting identified need immediate actions in order to promote a better treatment error reporting environment.

To describe a linear accelerator (linac) based magnetic resonance image guided radiation therapy system (MR-IGRT) and demonstrate the feasibility of delivering stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC) treatment. The linac-based MR-IGRT (MRL) system currently being installed at our institution integrates a 0.35T MRI with a flattening-filter free (FFF) linac delivering 6MV at 600 cGy/min. A novel double-focused and double-stack multileaf collimator (MLC) with an effective leaf width of 4 mm provides modulation for step-and-shoot IMRT delivery. The ability of a similar Cobalt-based system for real time, real anatomy gating has already been demonstrated, and a number of patients with NSCLC were treated. Here, we investigate the feasibility of planning and delivery with the linac-based system for SBRT, primarily focusing on plan quality as compared to conventional linacs (CL) and delivery times. Four MRL plans were generated for NSCLC patients who were previously planned and treated on a CL using 6MV FFF beams with a total dose of 54 Gy in 3 fractions. MRL plans were compared to clinical plans (CP) by evaluating conformity numbers with 100% (CN100), 95% (CN95) of prescription dose (Rx), heterogeneity indices (HI), maximum dose and dose-volume histograms of organs-at-risks (OARs), and delivery times. All MRL plans achieved PTV coverage and OAR sparing within clinical constraints and were comparable to clinically-treated plans as indicated in Table 1. Three plans showed an average of 8% and 12% improvement on PTV conformity CN100 and CN95, respectively. There is no clear trend for treatment time comparison but in general they only differ by 3 mins for a 10-min long treatment. The MRL is capable of generating clinically acceptable SBRT plans targeting NSCLC. With real-time MR gating, novel double-stack MLC design and fast FFF delivery, the system is able to achieve a more conformal and precise dose to the target therefore having great potential for further lung tumor dose escalation and reduction of treated volumes. We expect that a higher dose rate version will be available soon to further reduce the treatment time.Abstract 3536IDPlanTumor LocationVPTV Rx (%)VPTV 95%Rx (%)HICN100CN95Max Cord (Gy)Max Esophagus (Gy)Max Heart (Gy)Max Carina (Gy)Mean Lung-ITV (Gy)V20 Lung-ITV (%)Treatment time (min)1MRLLeft upper lobe97.999.61.160.920.844.4910.5521.828.843.193.110.2CP97.399.91.230.860.785.779.6818.519.223.023.07.22MRLLeft lower lobe99.11001.160.800.641.268.3310.970.452.412.45.7CP98.71001.150.840.690.456.2210.010.281.872.27.83MRLRight upper lobe99.299.91.160.740.665.138.670.730.781.210.711.8CP99.81001.170.720.581.418.160.310.421.081.09.04MRLLeft lower lobe97.299.71.260.890.8313.8714.0712.8912.676.216.26.9CP96.6991.200.780.709.5218.0115.6816.576.319.310.0 Open table in a new tab

Magnetic resonance image-guided radiation therapy (MR-IGRT) has been implemented at our institution since 2014. We report on the two-and-a-half year clinical experience in treating patients utilizing the world's first commercially available MR-IGRT system. Patients selected for MR-IGRT were enrolled on an IRB-approved prospective registry between January 2014 and June 2016. Patients were treated with a variety of RT techniques, including IMRT and SBRT, using a MR-IGRT system which consists of a split 0.35T MR scanner straddling a ring gantry with 3 MLC-equipped 60Co heads. When applicable, online or offline adaptation was performed and exception gating on sagittal 2D cine MR was utilized. The charts of patients treated with MR-IGRT were reviewed to report clinical and treatment parameters of initial patients treated with this novel technique. A total of 316 patients have been treated on the MR-IGRT system. Seventy-six (24.1%) patients were treated with 3D conformal RT, 146 (46.2%) patients were treated with IMRT, and 94 (29.7%) patients with SBRT. The most common disease sites treated were abdomen, 88 (28%); breast, 82 (26%); pelvis, 67 (21%); thorax, 61 (19%); and head and neck, 17 (5%) patients. Fifty-five (17.4%) patients were treated with online adaptive radiation therapy (ART) over a total of 232 adapted fractions to a variety of predominantly gastrointestinal sites. Cine MRI treatment gating was utilized for a total of 81 (25.6%) patients. All breast patients were treated with APBI. Forty-seven patients were enrolled on a clinical trial. MR-IGRT has been successfully implemented 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 using such techniques as SBRT and ART.

PurposeThe purpose of this study was to investigate and characterize the performance of a Multi Leaf Collimator (MLC) designed for Cobalt‐60 based MR‐guided radiation therapy system in a 0.35 T magnetic field.MethodsThe MLC design and unique assembly features in the ViewRay MRIdian system were first reviewed. The RF cage shielding of MLC motor and cables were evaluated using ACR phantoms with real‐time imaging and quantified by signal‐to‐noise ratio. The dosimetric characterizations, including the leaf transmission, leaf penumbra, tongue‐and‐groove effect, were investigated using radiosensitive films. The output factor of MLC‐defined fields was measured with ionization chambers for both symmetric fields from 2.1 × 2.1 cm2 to 27.3 × 27.3 cm2 and asymmetric fields from 10.5 × 10.5 cm2 to 10.5 × 2.0 cm2. Multi leaf collimator (MLC) positional accuracy was assessed by delivering either a picket fence (PF) style pattern on radiochromic films with wire‐jig phantom or double and triple‐rectangular patterns on ArcCheck‐MR (Sun Nuclear, Melbourne, FL, USA) with gamma analysis as the pass/fail indicator. Leaf speed tests were performed to assess the capability of full range leaf travel within manufacture's specifications. Multi leaf collimator plan delivery reproducibility was tested by repeatedly delivering both open fields and fields with irregular shaped segments over 1‐month period.ResultsComparable SNRs within 4% were observed for MLC moving and stationary plans on vendor‐reconstructed images, and the direct k‐space reconstructed images showed that the three SNRs are within 1%. The maximum leaf transmission for all three MLCs was less than 0.35% and the average leakage was 0.153 ± 0.006%, 0.151 ± 0.008%, and 0.159 ± 0.015% for head 1, 2, and 3, respectively. Both the leaf edge and leaf end penumbra showed comparable values within 0.05 cm, and the measured values are within 0.1 cm with TPS values. The leaf edge TG effect indicated 10% underdose and the leaf end TG showed a shifted dose distribution with 0.3 cm offset. The leaf positioning test showed a 0.2 cm accuracy in the PF style test, and a gamma passing rate above 96% was observed with a 3%/2 mm criteria when comparing the measured double/triple‐rectangular pattern fluence with TPS calculated fluence. The average leaf speed when executing the test plan fell in a range from 1.86 to 1.95 cm/s. The measured and TPS calculated output factors were within 2% for squared fields and within 3% for rectangular fields. The reproducibility test showed the deviation of output factors were well within 2% for square fields and the gamma passing rate within 1.5% for fields with irregular segments. The Monte Carlo predicted output factors were within 2% compared to TPS values. 15 out of the 16 IMRT plans have gamma passing rate more than 98% compared to the TPS fluence with an average passing rate of 99.1 ± 0.6%.ConclusionThe MRIdian MLC has a good RF noise shielding design, low radiation leakage, good positioning accuracy, comparable TG effect, and can be modeled by an independent Monte Carlo calculation platform.