1097 - Comparison of Online Adaptive SBRT to Non-Adaptive SBRT in the Treatment of Abdominal and Pelvic Oligometastasis: A Single-Institution Retrospective Analysis
Presenter(s)
T. W. Raclin1, O. Sager2, P. Dalwadi3, R. Beckert2, B. Kalaghchi2, J. W. Randall4, A. K. Bhatt2, M. Mahmood2, C. J. DeSelm5, F. Forghani2, E. Morris2, X. Zhao6, C. G. Robinson2, E. Laugeman2, P. Samson2, H. Kim7, and M. R. Waters2; 1WashU Medicine, Saint Louis, MO, 2WashU Medicine, Department of Radiation Oncology, St. Louis, MO, 3Washington University/B-JH/SLCH Consortium, St. Louis, MO, 4Department of Radiation Oncology, Northwestern University, Chicago, IL, 5Siteman Cancer Center, Barnes Jewish Hospital, Saint Louis, MO, 6Washington University in St. Louis School of Medicine, Department of Radiation Oncology, St. Louis, MO, 7Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA
Purpose/Objective(s): Online adaptive radiotherapy may improve the therapeutic ratio of stereotactic body radiotherapy (SBRT) for abdominopelvic metastases by accounting for daily anatomic variation and reducing organ-at-risk constraint violations. We compared local control, survival, and toxicity after online adaptive versus non-adaptive SBRT.
Materials/Methods: We retrospectively reviewed 365 consecutive patients treated with SBRT to abdominal or pelvic metastatic targets (2017-2025) at one institution. Online adaptive treatment was defined by an adaptive planning workflow performed at each fraction (n=201) versus non-adaptive image-guided SBRT (n=164). Time-to-event endpoints were measured from treatment end date. Local control (LC) was defined as time to local recurrence and censored at last follow-up or death. Overall survival (OS) was censored at last follow-up for living patients. Toxicity was recorded as maximum grade. Kaplan-Meier and Cox regression were used.
Results: Median age was 71 years. Online adaptive SBRT more frequently treated abdominal targets (78.6% vs 44.5%) and delivered higher median dose (50 Gy/5 fractions; BED10 100 Gy) than non-adaptive SBRT (35 Gy/5 fractions; BED10 59.5 Gy). Most patients were treated to a single metastatic lesion. At a median follow-up of 694 days among survivors, 23 local recurrences occurred. One-year local control was higher with online adaptive SBRT (98.5% vs 93.3%; log-rank p=0.013). In an exploratory multivariable Cox model excluding prostate cancer due to absence of local failures and adjusting for anatomic site, BED10, nodal status, and post-SBRT chemotherapy, online adaptive SBRT remained associated with improved local control (HR 0.30, p=0.012). One-year progression-free survival was numerically higher with online adaptive SBRT (55% vs 47%) but did not differ significantly (log-rank p˜0.18) and was not independently associated with treatment modality after adjustment on multivariate model. Grade =2 toxicity was uncommon and similar between groups (4.0% vs 6.1%, p=0.47); no grade =3 toxicity occurred after online adaptive SBRT.
Conclusion: In this large single-institution cohort of abdominopelvic metastases treated with SBRT, online adaptive radiotherapy was associated with improved local control without an increase in clinically significant toxicity, despite higher delivered dose. Prospective studies and methods to mitigate confounding are warranted.