2195 - MR-Guided Adaptive Radiotherapy (MRgART): A Multidisciplinary, Parallel Workflow Approach to Adaptive SABR Treatment.

02:30pm - 04:00pm PT

Hall F

Screen: 3

POSTER

Presenter(s)

Daniel Pham, PhD, CMD - Stanford Health Care, Stanford, CA

D. Pham¹, A. Pranoto², S. Godfrey², N. Ngo², Y. Gao¹, L. Skinner³, L. Vitzthum⁴, E. Rahimy⁵, and E. L. Pollom⁵; ¹Department of Radiation Oncology, Stanford University, Stanford, CA, ²Stanford Health Care, Palo Alto, CA, ³Department of Radiation Oncology, Stanford University, Palo Alto, CA, ⁴Stanford University School of Medicine, Stanford, CA, ⁵Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA

Purpose/Objective(s):

MR-guided adaptive radiotherapy (MRgART) provides an opportunity to re-optimize a treatment plan based on changes to patient anatomy on the day of treatment. The aim of this study is to report the resource utilization for SABR-based adaptive protocols within an academic institution.

Materials/Methods:

At our institution, a 0.35T MR-guided adaptive radiotherapy machine was updated in August 2024, allowing for parallel workflows by a multidisciplinary team for on-table adaptive treatment. All patients undergoing MRgART treatment were simulated on the MR-linac, prior to undergoing a CT scan for electron density mapping. In general, gastro-intestinal SABR patients were simulated with arms by the side. Patients were asked to fast at least 2 hours prior to MR simulation, and again for all subsequent treatment appointments. For liver lesions, Eovist was administered at least 15 minutes prior to MR imaging. All plans were generated using a 6MV FFF beam with fields ranging from 20 to 45, avoiding the arms. For treatment adaptation, the multidisciplinary team consisted of two radiation therapists, a dosimetrist, a medical physicist, and the attending physician. The adaptive workflow can be summarized into three stages with work done in parallel at each stage:

Stage 1 Patient setup and verification: Therapist and dosimetrist confirm localization to target with arms in correct position. Stage 2 Planning and QA: Dosimetrist/physicist update OARS and electron density map, physician update GTV volume and review OARs. Re-planning by dosimetrist, reviewed and QA’d by physician and physicist. Stage 3 Tracking setup and treatment: Target tracking structures confirmed and updated by therapist and physician.

Reports generated from each adaptive treatment session were reviewed to record time stamps at 1) initial target localization 2) planning approval and 3) end of treatment delivery.

Results:

From Sept 2024 through to Jan 2025, 47 patients with combined total of 203 fractions underwent MRgART. In order of most common sites treated to the least were liver, pancreas, abdominal node, and adrenals at 46.8%, 31.9%, 17%, and 4.3%, respectively. The dose prescriptions used varied by site: Pancreas/adrenals were prescribed 33- 50 Gy in 5 fractions; Liver 30 - 54Gy in 1 to 5 fractions; and abdominal nodes 40 – 60 Gy in 5 to 6 fractions. The median treatment duration, as measured from target localization through to end of treatment was 49 minutes (range: 19 min – 1hr 58min). The median planning and QA process was 21 minutes (range: 7 min – 54 min), and median time for target tracking setup and beam delivery was 25 minutes (range: 15 min – 1 hour 32 minutes). Overall, 83.3% (169 of 203) of fractions were within a 1-hour adaptive session.

Conclusion:

MRgART treatment is a complex process requiring communication between members of the multidisciplinary team. Our review of institutional data indicates that implementing a multidisciplinary approach with a parallel workflow can result in treatments within a one-hour timeframe.