1054 - Prospective Four Year Single Institution Outcomes of 1.5 Tesla MR Linac Based Radiotherapy from the MOMENTUM Study

A. M. Schottstaedt¹, L. A. Daamen², E. S. Paulson¹, X. Chen¹, E. A. Omari¹, A. Li¹, E. E. Ahunbay¹, B. A. Erickson¹, C. A. F. Lawton¹, C. J. Schultz³, L. Puckett¹, E. M. Gore¹, M. J. Awan¹, M. W. Straza Jr⁴, H. Verkooijen⁵, and W. A. Hall¹; ¹Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, ²Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, Netherlands, ³Medical College of Wisconsin, Milwaukee, WI, ⁴Department of Radiation Oncology, Froedtert & the Medical College of Wisconsin, Milwaukee, WI, ⁵University Medical Center Utrecht, Utrecht, Netherlands

Purpose/Objective(s): Treatment with external beam radiation therapy (RT) using a 1.5 Tesla (T) magnetic resonance linear accelerator (MRL) is a novel treatment modality that allows for real time, adaptive RT while taking advantage of improved contrast afforded by MR. Reported outcomes for MR guided RT (MRgRT) are scarce, generally low-field MRgRT (i.e. 0.35 T magnet), and have limited follow up of a few disease sites. We hypothesize good completion rate, toxicity, patient reported quality of life outcomes (PROs) and clinical outcomes for all patients treated at a single institution in the United States on the MRL. Materials/

Methods: Patients enrolled on the prospective MOMENTUM Study (NCT04075305) from July 2019 – March 2023 and treated at a single institution were included in the analysis. Prospective clinical data, technical data, Common Terminology Criteria for Adverse Events (CTCAEs) and PROs were obtained. Data was collected at baseline, 3, 6, 12, and 24 month follow-up. PROs collected included the EuroQol Five Dimension Five Level (EQ5D5L) and European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaires (QLQ).
Results: 186 total patients were enrolled, of which 96.5% completed treatment. Follow-up was completed by 91.4%, 78.0%, 62.9%, and 34.4% of patients at 3, 6, 12, and 24 months. The most frequently treated disease sites were pancreas (26%), liver (24%), prostate (15%), and brain (11%). Other treated sites (24%) include breast, lung, esophagus, head/neck, vagina, nodal regions, retroperitoneum, adrenal glands, bones, spinal cord, gallbladder, and pelvis. Adapt to position (ATP) was used in 69%, 29%, 36%, and 100% of liver, pancreas, prostate and brain patients. A total of 18 grade 3+ (G3) toxicities possibly or related to RT were reported. Acute G3 toxicity was seen in two liver, two pancreas, two prostate, and seven H&N treatments, and late G3 toxicity was seen in five pancreas treatments. PROs were completed in 51.4%, 45.8%, 48.2%, 46.5%, and 34.1% at baseline, 3, 6, 12, and 24 months follow-up for liver, pancreas, prostate, and brain patients. Statistically significant differences over time were increased pancreas PR25 pain scores, improved brain QLQC30 global health and physical functioning scores, decreased brain BN20 motor dysfunction and bladder control, and increased brain BN20 pruritus. EQ5D5L visual analog scale scores ranged from 70-78, 76-82, and 74-83 for liver, pancreas, and prostate, and improved from 71 at baseline to 79-88 during follow up for brain treatments.
Conclusion: We have presented single US institution prospective outcomes utilizing the 1.5 Tesla MRL, one of few experiences with high-field MRgRT. These results show a high completion rate with overall acceptable toxicity, clinical outcomes, and PROs in a cohort with a broad variety of malignancies, fractionation schedules, and treatment intentions.