ESTRO 2025 - Abstract Book

S237

Brachytherapy - Gynaecology

ESTRO 2025

Results: Dose de-escalation simulations in EMBRACE-II showed a reduction of organs-at-risk doses by 2-3Gy and 4 6GyEQD2 3 when CTV HR D90% was set to 85Gy versus 90GyEQD2 10 . On average, CTV HR D98% was 9-10Gy lower than CTV HR D90%. Consequently, for the RAPID protocol the ideal dose to CTV HR D98% was set to 80Gy for GTV res >5cm 3 and 75Gy when GTV res ≤5cm 3 . RAPID target doses, including ideal values and bounds are shown in Figure1. The planning study demonstrated the feasibility of implementing this protocol in all patients, resulting in very narrow variations in target prescription dose (Table1). For ‘small’ and ‘large’ GTV res , mean(1SD) CTV HR D98% were 75(0.5)Gy and 81(1.2)Gy, respectively, with similarly low variation for CTV HR D90% at 83(0.5)Gy and 91(0.8)Gy. This shows a reduced target dose variation (1SD<1Gy) compared to EMBRACE-II (1SD>3.5Gy). Likewise, for ‘small’/’large’ GTV res , bladder, rectum, sigmoid, and bowel D2cm 3 were 62Gy/63Gy, 53Gy/53Gy, 51Gy/62Gy, and 49Gy/50Gy, respectively, reflecting average OAR dose reductions of 8Gy, 6.5Gy, 9.0/0Gy, and 10Gy compared to the EMBRACE-II favorable risk-cohort treated with standard-of-care (1).

Conclusion: Transitioning from CTV HR D90% to D98% ensures a consistent BT dose prescription, providing a dose that represents the peripheral tumor region. Retrospective replanning demonstrated the feasibility of the new prescription protocol. The new prescription will be prospectively tested in the RAPID study.

Keywords: dose de-escalation, BT dose prescription

References: 1. Serban M, Gallois M, Urtubey T, Nout R, de Leeuw A, Fokdal L, et al. OC-0503 Effect of dose and fractionation de escalation in low-risk cervix cancer treated with EBRT and BT. Radiotherapy and Oncology. 2022;170:S451-S3

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Digital Poster MR-Guided Adaptive Brachytherapy using Geneva Applicator with or without Needle Loading in Locally Advanced Cancer Cervix - A Dosimetry Analysis Tanvee Singla 1,2 , Satyajit Pradhan 1,2 , Abhishek Shinghal 1,2 , Ankita Rungta Kapoor 1,2 , Chandrima Mukherjee 1,2 , Sanju Sanju 1,2 , Vinay Saini 1,2 , Ankita Pal 3,4 , Prashanth Giridhar 1,2 , Lincoln Pujari 1,2 , Ashutosh Mukherji 1,2