2934 - Dose-Response Relationship across Radiotherapy Modalities In Recurrent and Metastatic Ovarian Cancer: A Retrospective Analysis

Purpose/Objective(s):

Radiotherapy (RT) is increasingly used for recurrent and metastatic ovarian cancer; however, comparative data across modalities and dose–response relationships remain limited. We evaluated clinical outcomes and associations between biologically effective dose and disease control across stereotactic body RT (SBRT), conventional external beam RT (cEBRT), and intracranial RT.

Materials/Methods:

We retrospectively reviewed 59 ovarian cancer patients treated with RT between 2006–2025. Patients were categorized as SBRT (n=22), cEBRT (n=30), or intracranial RT (n=7). Median age was 62 years, and most patients had received =2 prior systemic therapy lines. Treatments were delivered primarily for oligometastatic or oligoprogressive disease. EQD2 (a/ß=10) was calculated when complete dose data were available (n=56). Associations between EQD2 and outcomes were analyzed using Spearman correlation. Survival was estimated by Kaplan–Meier methodology. Given substantial differences in tumor volume between SBRT and cEBRT groups, comparisons between modalities were descriptive.

Results:

Median follow-up was 20.7 months. Treated sites were predominantly extracranial pelvic disease and nodal targets: pelvis/pelvic mass 14/59 (23.7%), vaginal cuff/vagina 6/59 (10.2%), pelvic/iliac nodes 7/59 (11.9%), and para-aortic/retroperitoneal nodes 7/59 (11.9%); intracranial RT targets comprised 7/59 (11.9%), with remaining treatments involving less frequent or heterogeneous locations. Median EQD2 was similar between SBRT and cEBRT (40.0 vs 36.5 Gy, p=0.305), but dose per fraction differed significantly (6 vs 2.5 Gy, p<0.001). Across the full cohort, higher EQD2 correlated with lower 1-year failure (rho=-0.311, p=0.020). Within the cEBRT subgroup, EQD2 was significantly associated with lower 1-year failure (rho=-0.477, p=0.009). No significant dose–response association was observed within SBRT. In-field control at last follow-up was highest with SBRT (90.9%), followed by cEBRT (76.7%) and intracranial RT (57.1%). Two-year overall survival was 74.4% (SBRT), 48.1% (cEBRT), and 28.6% (intracranial RT).

Conclusion:

Higher EQD2 was associated with reduced 1-year disease failure, particularly within conventionally fractionated RT. No dose–response relationship was detected within SBRT. Observed differences in local control and survival across modalities should be interpreted cautiously due to substantial tumor burden variance and limited sample size. These findings are hypothesis-generating and highlight the need for further study of dose–response relationships in ovarian cancer radiotherapy.