Main Session
Sep
27
PQA 01 - Gastrointestinal Cancer and Central Nervous System
2208 - Ablative Stereotactic MR-Guided Adaptive Radiation Therapy for Anatomically Unfavorable Metastatic Colorectal Cancer
Presenter(s)
Kavita Sehrawat, MD - Baptist Health, Miami, FL
K. Sehrawat1, R. Herrera2, M. Ayala3, E. Y. Y. Akdemir4, T. Bejarano2, A. Kaiser1, R. Kotecha2, Y. Lee2, M. Hall2, S. Davis2, Y. Weiss2, A. Ucar5, F. de Zarraga5, S. Aparo5, R. P. Tolakanahalli1, A. Gutierrez1, K. E. Mittauer2, S. H. Demissie3, and M. D. Chuong1; 1Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 2Department of Oncological Sciences, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, 3Baptist Health South Florida, Miami, FL, 4Miami Cancer Institute, Miami, FL, 5Department of Medical Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL
Purpose/Objective(s):
Metastatic colorectal cancer (mCRC) is radioresistant and durable local control (LC) is most likely achieved with dose escalation to a biologically effective dose (BED10) >100 Gy10. However, treatment of mCRC lesions in proximity to radiosensitive organs-at-risk (OARs) often requires dose reduction to prioritize safety. Stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) may facilitate safe dose escalation for mCRC although published clinical outcomes are limited.Materials/Methods:
We performed a single institution retrospective cohort study of SMART for mCRC delivered on a 0.35-T MR-Linac between 2018-2025. SMART was delivered with continuous cine-MRI, soft tissue tracking, automatic beam gating, and online adaptive radiation therapy (oART) as needed from the GTV, respectively. Treatment response was assessed by RECIST 1.1 criteria. LC, progression-free survival (PFS), and overall survival (OS) were calculated using the Kaplan–Meier method. Prognostic factors for each were assessed using univariate (UVA). Toxicities were graded per CTCAE v5.0 as acute (=90 days) or late (>90 days) following SMART.Results:
62 patients with 98 metastatic lesions treated across 88 plans were analyzed. Median age was 67 years (range, 37-87). Most had metachronous metastases (87.5%), KRAS wild (54.5%), and microsatellite stable (75.5%) disease. 82% had chemotherapy prior to SMART. Target lesions included abdominal/pelvic lymph nodes (n=34), liver (n=30), lung (n=25), adrenal gland (n=5), abdominal wall (n=2), retroperitoneum (n=1), and pelvic implant (n=1). 39 (44.3%) were within 5 mm of a dose-limiting OAR. Median dose was 50.0 Gy (range, 25.0-60.0 Gy) in a median 5 fractions (range, 1-6); median BED10 was 100 Gy10 (range, 37.5-200 Gy10). Almost one-third of plans were prescribed 1 fraction to a median 34 Gy (BED10 149.6 Gy10). Median GTV and PTV volumes were 7.99(IQR, 2.75-18.94) and 19.45 cc (IQR, 10.21-41.73), respectively. Median follow up was 19.7 months. 2-year LC, PFS, and OS from SMART were 98.6%, 12.5%, and 87.6%, respectively. One local failure occurred in a lung metastasis nearly 2 years after SMART. No factors were associated with LC or PFS. On UVA, worse OS was associated with larger GTV (HR 1.005, 95% CI: 1.002-1.009; P=0.003) and KRAS mutation (HR 3.516, 95% CI: 0.964-12.822; P=0.057) while improved OS was associated with 2 vs. 0-1 lines of prior systemic therapy (HR 0.0188, 95%: CI 0.076-0.792; P=0.019). Acute and late grade 3 toxicities occurred in 0 and 1 patient (abdominal pain), respectively, and there were no grade 4-5 events.Conclusion:
To our knowledge, this is the largest analysis of SMART for mCRC in which durable LC was safely achieved in nearly all patients despite most lesions being mobile and in proximity to dose-limiting OARs.