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

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.

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.

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.

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.