Highlights Radiation is not typical in the standard of care for cardiac metastases. MR-guided radiation uses real-time imaging and offers better soft tissue contrast. Real-time MR-guidance allows for safe high dose radiation to cardiac metastases. MR-guided stereotactic radiation can improve symptoms without acute toxicity.

Purpose/Objective(s): Whole brain radiotherapy with hippocampal avoidance (HA-WBRT) is a technique utilized to treat metastatic brain disease while preserving memory and neurocognitive function. We hypothesized that the treatment planning and delivery of HA-WBRT plans is feasible with an MRI-guided linear accelerator (linac) and compared plan results with clinical non-MRIguided C-Arm linac plans. Materials/Methods: Twelve HA-WBRT patients treated on a non-MRI-guided C-Arm linac were selected for retrospective analysis. Treatment plans were developed using a 0.35T MRI-guided linac system for comparison to clinical plans. Treatment planning goals were defined as provided in the Phase II Trial NRG CC001. MRI-guided radiotherapy (MRgRT) treatment plans were developed by a dosimetrist and compared with clinical plans. quality assurance (QA) plans were generated and delivered on the MRI-guided linac to a cylindrical diode detector array. Planning target volume (PTV) coverage was normalized to ∼95% to provide a control point for comparison of dose to the organs at risk. Results: MRgRT plans were deliverable and met all clinical goals. Mean values demonstrated that the clinical plans were less heterogeneous than MRgRT plans with mean PTV V37.5 Gy of 0.00% and 0.03% (p = 0.013), respectively. Average hippocampi maximum doses were 14.19 ± 1.29 Gy and 15.00 ± 1.51 Gy, respectively. The gamma analysis comparing planned and measured doses resulted in a mean of 99.9% ± 0.12% of passing points (3%/2mm criteria). MRgRT plans had an average of 38.33 beams with average total delivery time and beam-on time of 13.7 (11.2-17.5) min and 4.1 (3.2-5.4) min, respectively. Clinical plan delivery times ranged from 3 to 7 min depending on the number of noncoplanar arcs. Planning time between the clinical and MRgRT plans was comparable. Conclusion:This study demonstrates that HA-WBRT can be treated using an MRI-guided linear accelerator with comparable treatment plan quality and delivery accuracy.

Materials/Methods: Modern treatment planning systems (TPS) cannot design, calculate, or optimize treatment plans utilizing continuous couchbased delivery. Based on the current limitation of modern TPS, the need to plan dynamic couch-based dose delivery arises for our investigation. We implement an automatic method utilizing the TPS scripting application programming interface (ESAPI). Additionally, we introduce a novel gantry static couch motion technique (GsCM) with static gantry positions and dynamic couch motion for brain treatment. The script interface allows selection of PTV, adding MLCs and PTV margin, choosing the number of fields, and initiation of the dose calculation within the TPS environment. We can automatically design custom treatment plans with simple 3-dimentional (3D) planning and conformal arc. This script based automated planning was retrospectively applied to brain patients (n = 5) using 200 cGy for 23 fractions. Initial development required implementing a conversion from the TPS mechanical axes to that of the machine. The readable Extensible markup language (XML) files are generated in the TPS environment using ESAPI by combining the fields at each couch position into a single deliverable field for each gantry angle utilizing continuous couch motion. The entire workflow is feasible within our script interface. The last part of this study focused on verifying the dose delivery. We used an ion chamber array positioned in the vertical direction to avoid side beam entrance. Trajectory log files were also analyzed using root mean square error (RMSE) to verify the MLC, gantry, and couch position accuracy. Results: All treatment plans satisfy the criteria of V100% ≥ 95% and respect the dose to organs-at-risk (OARs). Automated script-based plans took less than a minute (excluding dose calculation) to design as compared to manual planning (2-8 hours per plan). The delivery was found to be less than 2 minutes for two 90 degrees partial arcs as compared to field-by-field delivery (15-30 minutes based on the plan type). All script-based plans (n = 5) passed patient-specific QA (> 95%) using the criteria of 2 mm distance to agreement and 2% dose difference. The couch rotational RMSE error for step and shoot and continuous delivery was 0.1 degrees and 0.12 degrees, respectively. MLC RMSE was 0.005 mm, and 0.006 mm for step and shoot and continuous delivery. Conclusion:The results of our study indicate that the automated custom planning with couch motion is feasible and comparable with clinical planning in terms of dosimetric quality. The developed methodology provides a tool that is integratable with the current TPS without any additional resources. It designs script-based plans for dynamic couch motion-based dose delivery.