The Role of Stereotactic Body Radiotherapy (SBRT) in Oligometastatic and Oligoprogressive Gynecologic Malignancies: A Multi-Institutional Pooled Analysis

Abstract

The optimal use of stereotactic body radiotherapy (SBRT) for the diverse group of patients with gynecologic malignancies has not been clearly defined. This multi-institutional pooled analysis aims to characterize the use of SBRT for different primary disease types and indications within the gynecologic cancer population.Patients treated with SBRT at three institutions with oligometastatic (OM) disease (5 or fewer sites), oligoprogressive (OP) disease (limited areas of progression with controlled systemic disease), or progression in an eloquent area were included. Descriptive statistics were used to report patient and treatment characteristics and toxicity. Local recurrence-free survival (LRFS), distant progression-free survival (DPFS), salvage chemotherapy-free survival (CFS, excluding patients on systemic therapy at time of SBRT) and overall survival (OS) probabilities following SBRT were calculated using Kaplan-Meier methods. Associations with disease and tumor factors were examined using Cox regression methods.One hundred forty-four patients (144) with gynecologic cancers were treated with SBRT to 206 lesions. The median age was 61 (range 46-86) and median follow up was 16.6 months (range 0.5-106.8). Patients had cancers of the uterus (n = 101), ovary (n = 67), cervix (n = 27), and vulva or vagina (n = 8). Lesions were considered OM (n = 124), OP (n = 68), or progressive in an eloquent area (n = 14). Treatment was delivered to lesions in the pelvis (n = 50), lung (n = 40), para-aortic region (n = 37), abdomen or liver (n = 36), bone (n = 31), and distant nodes (n = 10). SBRT dose ranged from 20-60Gy (median 40Gy) in 2-5 fractions. Twenty-three (11.1%) lesions recurred locally after SBRT. Median LRFS was 23.9 months (95% CI 20.2-27.5), DPFS was 10.7 months (95% CI 10.7-16.9), and OS 22.9 months (95% CI 12.8-31.3). LRFS was 73.0% and 47.8%, DPFS was 44.2% and 19.6%, and OS was at 72.9% and 46.6% 1 and 2 years respectively. Twenty-nine percent of patients received salvage systemic therapy, and median CFS was 14.1 months (95% CI 10.4-17.8). On multi-variable analysis, only higher BED (OR 0.98, P = 0.013) was associated with LRFS. Primary disease type, tumor size, dose of radiotherapy, nodal versus non-nodal target, and DFI were not significantly associated with OS or DPFS on MVA.This large cohort of patients receiving SBRT for oligometastatic and oligoprogressive gynecologic cancers had excellent tumor control, and promising DPFS and OS. Local control appears to be related to SBRT dose. SBRT may have the potential to delay time to initiation of chemotherapy or targeted therapies in select gynecologic cancer populations. Further prospective studies are required to determine which primary disease types benefit most from SBRT, and to establish the optimal sequencing of SBRT with other oncologic treatments.