E. Y. Y. Akdemir1, M. D. Chuong1,2, R. Herrera1, A. Kaiser1,2, T. Kutuk1, A. La Rosa1, K. E. Mittauer1,2, N. Bassiri-Gharb1,2, R. P. Tolakanahalli1,2, A. Gutierrez1,2, M. P. Mehta1,2, and R. Kotecha1,2; 1Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 2Florida International University, Herbert Wertheim College of Medicine, Miami, FL
Purpose/Objective(s): Magnetic resonance (MR)-guided stereotactic body radiation therapy (MR-SBRT) facilitates dose escalation to oligometastatic targets in close proximity to gastrointestinal organs-at-risk (OARs) given excellent soft tissue visualization, automatic beam gating, and on-table adaptive workflow to account for interfraction anatomic change. The objective of this study was to report the outcomes of patients treated with MR-SBRT in the infra-diaphragmatic (ID) region to characterize dose-response relationships associated with tumor control, characterize patterns of failure, and report on long-term treatment-related toxicities. Materials/
Methods: We retrospectively evaluated patients =18 years old treated for up to 5 oligometastases (OM) treated with MR-SBRT between May 2018 and August 2023. Patients were categorized as oligorecurrent, oligoprogressive, or oligopersistent. Local control (LC) and distant progression-free survival (DPFS) from the time of MR-SBRT were calculated using the Kaplan-Meier method. Results: In total, 143 patients were prescribed a median 50 Gy in 5 fractions (Range: 25-60 Gy; 1-6 fractions) to 181 targets over 170 SBRT courses. On-table treatment adaptation was required for 635/860 (73.8%) of delivered fractions. The most common primary tumors were lung (37.7%), colorectal (18.2%), and gynecologic (14%). Target lesions mainly included lymph nodes (LNs) or peritoneal implants (39.2%), adrenal glands (30.4%), and liver (21%). Most patients (46.1%) presented with oligorecurrent disease, followed by oligoprogressive (42.0%) and oligopersistent disease (11.9%). The 1-, 2-, and 3-year actuarial LC rates were 89.3% (95% CI: 84-94.6%), 78% (95% CI: 69.7-86.1%), and 73.1% (95% CI: 63.1-83.1%), respectively. Longer median DPFS trended towards significance for non-oligoprogressive vs. oligoprogressive OM (10.9 vs. 5.9 months), p=0.062. The prescribed dose for colorectal and non-colorectal cancers was similar; the prescribed median BED10 was 101.1 Gy (Range: 38.9-225.5) vs. 103.2 Gy (Range: 39.6-184.2), respectively, and 2-year LC was 77.7% (95% CI: 60-94%) and 77.6% (95% CI: 68.2-87%), respectively. Almost all patients with local failure also had concurrent distant failure (DF) (21/22, 95%). Grade 3 or higher late toxicity was uncommon, with a 1 to 3-year actuarial rate of 1.4% (95% CI: 0-4.1%). Conclusion: In this large and heterogenous cohort of patients with ID metastases treated with ablative intent MR-SBRT, we found high and durable rates of local control regardless of histology, modest DPFS rates, and an excellent toxicity profile. Adaptive replanning was frequently required due to anatomically unfavorable target lesion locations. Expectedly, DF continues to be an important issue in the management of oligo-progressive patients.
