18F-FDG PET/CT guided salvage radiotherapy strategies for lymph-nodal relapses in gynecological cancers: SBRT vs ENRT

Objective: To identify outcome differences between extended nodal radiotherapy (ENRT) with simultaneous integrated boost (SIB) and stereotactic body radiotherapy (SBRT), performed with advanced radiotherapy techniques, both of which were 18F-Fluoro-Deoxy-Glucose (FDG) PET/CT guided, for lymph-node (LN) relapses of gynecological tumors, and to identify the most important determining factors. Methods: Records of gynecologic patients treated in a single-institution with FDG PET/CT guided intensity-modulated radiotherapy (IMRT), image-guided radiotherapy (IGRT), or SBRT, were reviewed, and only patients at first salvage radiotherapy for LN relapses were considered. Local relapse-free- (LRFS), regional relapse-free- (RRFS), distant metastasis-free- (DMFS), disease-free-(DFS) and overall-survival (OS), as well as acute and late toxicity (with CTCAE v5.0 score), were determined. Results: Fifty-eight patients (23 ENRT+SIB; 35 SBRT) treated for 178 LNs from February 2007-April 2023, were identified. Median biological equivalent dose (BED10) delivered to PET-positive LNs was 76.5 Gy (Interquartile range-IQR- 74.4;78.7) for ENRT, and 72 Gy (IQR 59.5;75.6) for SBRT. Median follow-up was 81.1(IQR 48.5; 117.2) and 37.0 (IQR 21.3; 58.4) months for ENRT and SBRT, respectively. Thirty-six-month estimated LRFS was 90.2% for ENRT and 82.6% for SBRT; RRFS was 69% and 63.4%, DMFS 26.1% and 44.3%, and OS 73.7% and 60.4%; no statistically significant differences were found between the two groups (logrank test, p= 0.29). ENRT recorded more acute (p⩽0.033), but not late, toxicities. Conclusions: ENRT+SIB and SBRT for gynecological LN tumor relapses obtain similar results in terms of disease-free and OS, with fair toxicity. Prospective studies with higher patient numbers are needed.