ESTRO 2025 - Abstract Book

S242

Brachytherapy - Gynaecology

ESTRO 2025

on dose-volume parameters, rectum and bladder toxicities, and quality of life (QOL) in cervical cancer patients undergoing MR-IGABT.

Material/Methods: A prospective randomized controlled trial was conducted with 20 patients randomized into HGI and non-HGI group. In HGI group, 2-6 cc of HG was injected into retrocervical space to maintain at least 1-cm distance between cervix and rectum during each fraction of brachytherapy. Dose-volume parameters including high-risk clinical target volume (CTV HR ) D90, CTV HR D98, rectum D2cc and bladder D2cc were reported as total equivalent dose in 2 Gy fractions, combining a whole pelvic radiation dose of 50.4 Gy in 28 fractions with brachytherapy dose of 8 Gy for 3 fractions.

Results: Mean rectum D2cc was 64.9±5.7 Gy in HGI group and 66.8±4.7 Gy in non-HGI group (p=0.446). Mean bladder D2cc was 79±3 Gy and 83±6 Gy (p=0.094) in HGI and non-HGI group. There was no significant difference in CTV HR D90 (91.6±4.4 Gy and 92.3±2.9 Gy, p=0.698) and CTV HR D98 (83.4±3.5 Gy and 82.8±2.9 Gy, p=0.686) between HGI and non-HGI group. Mean gel volume per injection was 3.6±2.2 cc, gel thickness was 1.3±0.6 cm and change of the distance from CTV HR to rectum between pre-brachytherapy and post-HGI was 1.8±1.1 cm. Analysis revealed a correlation between gel thickness and change of the distance from CTV HR to rectum (R=0.54, p=0.004), as well as between rectum D2cc and distance from CTV HR to rectum (R=-0.58, p=0.002). Rectum D2cc showed a trend towards correlation with gel thickness (R=-0.38, p=0.051). Cumulative grade 2 early rectal toxicities were 3.5% and 2.8% in HGI and non-HGI group. No grade 3-4 early rectal toxicity was reported. There was no early grade ≥2 bladder toxicity. Changes in QOL score at 1 and 3-month post-treatment were comparable between groups. There was no serious adverse event from HGI and gel was undetectable on follow-up MRI at 3 months. Conclusion: HGI is safe and feasible for cervical cancer patients undergoing MR-IGABT. Although HGI did not significantly reduce rectum dose, correlations were observed between rectum D2cc, distance from CTV HR to rectum and gel thickness. Further studies are needed to investigate the efficacy of HGI and determine factors for patient selection in this context.

Keywords: Spacer, Hyaluronate gel, MR-IGABT, Cervical cancer