Role of the gel spacer in safely delivering whole pelvic radiation therapy without central shielding in computed tomography-based image-guided adaptive brachytherapy for uterine cervical cancer patients

Abstract

BackgroundTo protect the rectum and bladder from high dose exposure, the Japanese guidelines for managing uterine cervical carcinoma recommend pelvic irradiation with central shielding (CS). Conversely, the European Society for Radiotherapy and Oncology (ESTRO) and the American Brachytherapy Society (ABS) guidelines recommend delivering ≥ 85 Gy to high-risk clinical target volume D90 (CTVHR D90%). In this study, we investigated whether a gel spacer can enable the safe delivery of the ESTRO/ABS-recommended doses to the target while observing dose constraints for the OARs without using CS in external beam radiation therapy (EBRT). Materials and MethodsTwenty patients who received definitive radiation therapy without CS and were treated by brachytherapy with a gel spacer between April 2017 and May 2022 were retrospectively reviewed. The cumulative doses of EBRT and brachytherapy expressed in the form of the equivalent dose in 2 Gy fractions (EQD2) were calculated. Treatment outcomes and incidence of adverse events were also examined. ResultsThe median cumulative CTVHR D90%, rectum D2cm3, and bladder D2cm3 were 86.6 Gy (range, 69.8–103.7), 62.9 Gy (range, 55.3–72.5), and 72.0 Gy (range, 62.9–84.1), respectively. The median follow-up was 35.9 months (range, 10.9–70.3). The 2-year local control rate was 95% (95% CI: [69–99%]). There were no CTCAE ≥Grade 3 late gastrointestinal or genitourinary adverse events. ConclusionsThe use of gel spacer can enable ESTRO/ABS-recommended dose constraints even without using CS in EBRT, with favorable outcomes and low adverse event rates.