ESTRO 2025 - Abstract Book

S274

Brachytherapy - Gynaecology

ESTRO 2025

References: 1. Pötter R, Chargari C, et al. MRI-guided adaptive brachytherapy in locally advanced cervical cancer (EMBRACE-I): a multicentre prospective cohort study. Lancet Oncol. 2021;22(4):538-547. 2. Sturdza A, Pötter R, Fokdal LU, Haie-Meder C, Tan LT, Mazeron R, Petric P, Šegedin B, Jurgenliemk-Schulz IM, Nomden C, et al. Image guided brachytherapy in locally advanced cervical cancer: Improved pelvic control and survival in RetroEMBRACE, a multicenter cohort study. Radiother Oncol. 2016;120(3):428-433. doi:10.1016/j.radonc.2016.03.011.

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Digital Poster Interfraction dosimetric evaluation method in image-guided-adaptive brachytherapy in locally advanced cervical cancer. Sara Montemuiño Muñiz 1 , Aldara Candal Meléndrez 1 , Francisco Mosquera-Pena Sánchez 2 , Benito Andrade Álvarez 2 , Daniela Medal Francesh 2 , Beatriz Vázquez Barreiro 1 , Elena Hernández Piñeiro 1 , Guillermo Cameselle Gallego 1 , Victor Muñoz Garzón 1 1 Radiation Oncology, Hospital do Meixoeiro, Vigo, Spain. 2 Radiation Physics, Hospital do Meixoeiro, Vigo, Spain Purpose/Objective: We conducted an Interfraction Dosimetric Evaluation (IDE) method to evaluate the clinical target volumes (CTV) and organs at risk (OAR ) in cervical Image-Guided-Adaptive HDR-Brachytherapy (HDR-IGABT). Material/Methods: Locally advanced cervical cancer were treated with Cisplatin-based chemoradiotherapy (ChRT) followed by 7Gy x 4 fractions of HDR-IGABT. We performed two applications one week apart, with 2 daily fractions separated by at least 6 hours. First intracavitary BT-application plan was performed on MRI/CT data set with Oncentra System®. In the second fraction of each application, a new CT was performed to verify the implant position, contour the OARs and transfer the CTVs and isodose curves from the previous CT. After 12 procedures performing a visual clinic method, we implemented the following method: the intersections of 7.8 and 7.2Gy isodoses (Equivalent Dose in 2Gy Fractions (EQD2) 90 and 85Gy respectively) with CTV-HR (high risk) and 3.5Gy (60Gy EQD2) with CTV-IR (intermediate risk) were identified. For OARs, the intersection of 5Gy isodose (75Gy EQD2) with rectum, small-bowel, and sigmoid, and 6.3 Gy intersection with the bladder (90Gy EQD2) were identified. Plans were optimized when OAR exceeded 2 cm 3 and/or targets coverage was compromised. Results: 41 procedures in 21 patients treated between april 2023-2024 were analysed, 29 procedures using the IDE method. The mean V90Gy and V85Gy CTV-HR and V60Gy CTV-IR coverage was 84.9%, 88% and 98.3%, respectively. The intersection isodose level with bladder, rectum, sigmoid and small-bowel was: (0.7+0.9)cc, (0.7+1.6)cc, (0.7+1.4)cc, (1+1.9)cc, respectively (mean+SD). For the OAR, 4 procedures did not meet criteria in bladder, 5 in rectum, 3 in sigmoid and 5 in small bowel. Action was only required (treatment replan) in 5 (17%) procedures evaluated with IDE method. In cases where action was not required were: impossibility for achieving CTV coverage in the morning plan, not repercussion in cumulative EQD2 and change in conditions (e.g. gas phased out).