Clinical outcomes of stereotactic body radiation therapy to the liver.

565 Background: Stereotactic body radiation therapy (SBRT) can accurately and effectively target liver lesions with an ablative dose. However, prior studies suggest that SBRT directed at tumors near the central hepatobiliary tract may lead to downstream toxicity including biliary stricture and impaired liver function. This study aims to evaluate clinical outcomes and hepatobiliary toxicities associated with SBRT to the liver. Methods: This retrospective study reviews 177 patients who received CT- or MR-guided SBRT to the liver at Dana-Farber Cancer Institute and Brigham and Women’s Hospital from 2010 to 2024. Patient demographics, treatment characteristics, and clinical outcomes were extracted from electronic medical records. Local control, regional control, and overall survival were assessed using Kaplan-Meier methods. Toxicity was evaluated by tracking the incidence of biliary stricture requiring intervention and Child-Pugh (CP) scores pre- and post-SBRT. Results: Of the 177 patients, 47 (26.6%) had primary disease and 130 (73.4%) had metastatic disease, with a median follow-up of 58.7 months. Among those with primary disease, 9 (19.1%) had post-SBRT local progression (median time to progression not reached, 95% CI: 47.3, NA) and 26 (55.3%) had regional progression (median time to progression of 20.5 months, 95% CI: 6.5, 58.1). Of patients with metastatic disease, 44 (33.8%) had local progression (median time to progression of 40.2 months, 95% CI: 23.0, NA) and 96 (73.8%) had regional progression (median time to progression of 5.9 months, 95% CI: 4.8, 9.3). Median overall survival post-SBRT was 34.6 months for primary disease (95% CI: 20.2, 57.7) and 23.6 months for metastatic disease (95% CI: 19.0, 28.8). 18 patients (10.1%) later developed biliary stricture requiring intervention (12.8% of primary disease and 9.2% of metastatic disease). Of the 119 patients with CP scores available, 59 patients (49.6%) had a maximum post-SBRT CP score increase of 2 or more (55.0% of primary disease, 46.8% of metastatic disease). Conclusions: This study demonstrates that SBRT is an effective treatment option for local control in the liver, with better survival and progression outcomes for primary disease compared to metastatic disease. Among potential post-SBRT toxicities, initial analysis indicates frequent increase in CP score and low incidence of biliary stricture requiring intervention. An ongoing analysis will explore whether the dose to central bile ducts correlates with late strictures and toxicities.