3496 - Comparing Stereotactic Body Radiation Therapy and Hypofractionated Radiation for Unresectable Intrahepatic and Perihilar Cholangiocarcinoma: A Retrospective Analysis

Purpose/Objective(s): While conventional radiation dosing has historically been correlated with poor rates of local control for cholangiocarcinoma, both high-dose hypofractionated (HRT) and Stereotactic Body Radiation (SBRT) appear more promising, though with limited available data in this rare disease. This study aims to evaluate local control (LC), treatment-related toxicity, and other oncologic outcomes in patients treated with HRT or SBRT for stage I-III intrahepatic and perihilar cholangiocarcinoma.

Materials/Methods: We reviewed 87 patients treated with definitive-intent radiation within a multi-center hospital system (2011–2024), excluding those receiving conventional fractionation, mixed treatment techniques and those with nodal or distant metastasis, leaving 50 for analysis. Treatment decision for HRT or SBRT was made by the treating radiation oncologist based on meeting perceived normal tissue tolerance constraints. Baseline characteristics, radiation details, and outcomes were assessed. The primary endpoint was LC; secondary endpoints included overall survival (OS) and toxicity. LC and OS were estimated using Kaplan-Meier methodology.

Results: Median age was 67 years (range: 29–97), median KPS 90 (range 70-90), and median follow-up 7.9 months (range: 0.4–154.5). Patients received either HRT [51–67.5 Gy in 12–15 fractions, median 60 Gy/15 fractions] or SBRT [30–60 Gy in 3–5 fractions, median 50 Gy in 5 fractions (n=11)]. Mean tumor size was larger in the HRT cohort (6.3 cm vs. 3.3 cm, p=0.0002). LC at 9 months was 59.3% for HRT and 88.7% for SBRT (p = 0.008). OS at 1 and 2 years was 63.9% and 32.0% for HRT vs. 65.3% and 54.4% for SBRT (p=0.26).

For further analysis, patients were stratified based on BED10: Group A (mean 80, range 48-90, n = 18), Group B (mean 103, range 95-115, n = 21), and Group C (mean 172, range 150-180, n = 11). Mean tumor size was largest in Group A (5.4 cm vs 4.3 cm vs 3.4 cm). Pre-RT systemic therapy was used in 66% (Group A), 23% (Group B), and 45% (Group C). Local control at 2 years was 55% (Group A), 81.7% (Group B), and 83.3% (Group C) (p=0.26). Overall survival at 2 years was 53% (Group A), 51% (Group B), and 50% (Group C) (p=0.72), with median survival of 31.1, 24.3, and 27.6 months, respectively. Toxicity included two grade 2 events (Group A, Group B) and one grade 3 event (Group C).

Conclusion: While the use of SBRT and higher BED radiation appear to be correlated with improved local control this is confounded by tumor size and location in this retrospective review with risk-adapted dosing. Given overall limited treatment-related toxicity and similar overall survival in all groups, this appears to support the use of a risk-adapted dose strategy aiming for the highest possible BED, though converting to a hypofractionated approach when unable to achieve SBRT dose constraints due to tumor size or location.