ESTRO 2025 - Abstract Book

S825

Clinical - Gynaecology

ESTRO 2025

Conclusion: In this series, adjuvant radiotherapy for EC achieved excellent local control rates and global QoL, but poor sexual health outcomes.

Keywords: Quality of life, Sexual Health, Adjuvant RT

References: Concin N. Int J Gynecol Cancer 2021;31:12 39 Samper Ots PM. Clin Transl Oncol. 2021 Jun;23(6):1193 1200

León-Castillo A, de Boer SM, Powell ME, Mileshkin LR, Mackay HJ, Leary A, et al. Molecular Classification of the PORTEC-3 Trial for HighRisk Endometrial Cancer: Impact on Prognosis and Benefit From Adjuvant Therapy. J Clin Oncol 2020;38(29):3388-97. Gil Haro B., Cordoba Largo S, Rodriguez I, et al. Let´s talk about sex: Consensus guidelines of the GINECOR working group of the Spanish Society of Radiation Oncology. Clinical recommendations after pelvic radiotherapy. In press.

2292

Mini-Oral Impact of bone marrow sparing on normal tissue complication probability of haematological toxicity for VMAT in locally advanced cervical cancer Po Tsz Wong 1 , Nelson Tsz Cheong Fung 2 , Elki Sze Nga Cheung 1 , Philip Yuguang Wu 1 1 Department of Clinical Oncology, Pamela Youde Nethersole Eastern Hospital, Hong Kong, Hong Kong. 2 Department of Medical Physics, Pamela Youde Nethersole Eastern Hospital, Hong Kong, Hong Kong Purpose/Objective: Hematological toxicity (HT) is a significant but often underreported effect of external beam radiotherapy in locally advanced cervical cancer (LACC), which may bring detrimental impact on treatment tolerance and compliance. Despite growing interest in bone marrow sparing (BMS), clear dose-response relationships for HT have not been established, particularly in extended-field radiotherapy (EFRT). This study aims to investigate the dosimetric and clinical impact of BMS in LACC, and derive a feasible BMS strategy for clinical utilization. Material/Methods: LACC patients receiving EFRT (N=37) or pelvis-only radiotherapy (PORT) (N=37) with concurrent chemotherapy followed by brachytherapy were included for retrospective analyses. Radiotherapy techniques followed the EMBRACE-II study. The outer contour of bones were delineated as a surrogate for BM. Incidence of HT from baseline to 2 months post-treatment were graded according to NCI-CTCAE v5.0. BM dose and HT were compared between the EFRT and PORT groups. Dose-response relationships for HT were examined using univariate logistic regression analysis. Lyman-Kutcher-Burman normal tissue complication probability (NTCP) models were developed for HT prediction. VMAT plans were generated to simulate the dosimetric effect of BMS in 20 EFRT and 20 PORT cases to establish BM dose constraints, based on pre-requisites of achieving mandatory planning aims while maintaining plan quality similar to the original plans. Results: Compared to PORT, patients receiving EFRT had 10-17% higher BM dose across V 5-35Gy and experienced higher incidence of ≥ G3 neutropenia (p=0.047) and G4 lymphopenia (p<0.001). Overall, various dose-volume parameters of BM across 5-45Gy were found to be associated with ≥ G3 leukopenia, ≥ G2 thrombocytopenia, ≥ G3 neutropenia and G4 lymphopenia. Age and baseline marrow function showed no correlation. With BMS, the NTCP of ≥ G2 thrombocytopenia, ≥ G3 neutropenia and G4 lymphopenia could be reduced by 15-38% for EFRT and 6-8% for PORT, at the expense of an acceptable increase in bowel dose. For EFRT, it is recommended to limit the BM V 10Gy , V 20Gy and V 35Gy to <80%, <60% and <30%, respectively, to reduce the NTCP of thrombocytopenia, neutropenia and lymphopenia