3412 - Feasibility of 3 Fraction Treatment Using Stereotactic Magnetic Resonance - Guided Adaptive Radiation Therapy in Single or Three Fractions for Oligometastases in the Abdomen and Pelvis: Results from the Phase I SMART-STOP 3-Fraction Cohort
Presenter(s)
Z. L. Cosner1, Y. H. Chen2, D. D. Yang3, G. Benham4, S. Chirmade4, K. J. Fitzgerald5, R. H. Mak6, S. Tanguturi3, J. E. Leeman7, R. van Dams3, Z. Han7, and M. A. Huynh8; 1Harvard Radiation Oncology Program, Boston, MA, 2Dana Farber Cancer Institute, Boston, MA, 3Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA, 4Department of Radiation Oncology, Brigham and Women’s Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, 5Department of Radiation Oncology, Brigham and Women’s Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, NY, 6Department of Radiation Oncology, Brigham and Women's Hospital/Dana-Farber Cancer Institute, Boston, MA, 7Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, 8Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA
Purpose/Objective(s): Stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) using a 5-fraction approach has been shown to be a feasible and effective method for delivering ablative radiation therapy to abdominopelvic metastases. The goal of this study was to determine the feasibility, and safety of a three-fraction approach to SMART.
Materials/Methods: 10 patients with abdominopelvic oligometastases were consecutively enrolled on SMART-STOP under the 3-fraction arm (NCT04115254). These patients were treated with 3 fraction SMART-STOP on a 0.35T magnetic resonance linear accelerator (MR linac) at a single institution from September 2022 to October 2024. Local failure, progression and survival rates were analyzed using Kaplan-Meier statistics.
Results: Overall, 11 tumors were treated in 10 patients, with the most common histology being prostate adenocarcinoma (7 patients, 70%). Six sites (55%) were centered in the abdomen, and 5 (45%) in the pelvis. Two tumors (18%) were at sites of prior radiation. Nine tumors (82%) were treated to 10Gy x3, and 2 (18%) were treated with 9Gy x 3. Online adaptation resulted in a clinically significant improvement in coverage or organ sparing in 79% of delivered fractions. Breath hold respiratory gating was used in 4 cases (36%). The median time required for adaptation was 15 minutes, and the median time in the treatment room was 41 minutes. Zero patients experienced local failure, with 1-year local control of 100% and a median follow-up of 11.6 months. Four patients had distant failure with 1 year progression free survival rate of 64.3%, and median time to progression of 22 months. One-year survival rate was 100%. No patients developed Grade 3 or higher toxic effects, 2 patients (20%) experienced grade 2 toxicity (nausea, rectal frequency). The most common toxicity was grade 1 fatigue in 7 patients (70%). There is no significant change in patient reported outcome measures from baseline compared to follow up assessments immediately after treatment and up to 1 year post-treatment.
Conclusion: 3 fraction SMART was feasible and safe for delivering ablative radiation therapy to abdominopelvic oligometastases. Adaptive planning was necessary for the majority of cases to either improve target coverage or spare organs-at-risk. Preliminary data provides evidence of efficacy which will be further tested in a Phase II trial.