ESTRO 2025 - Abstract Book

S249

Brachytherapy - Gynaecology

ESTRO 2025

Keywords: Deep Learning, automated applicator reconstruction

References: [1] van Vliet-Pérez SM, van Paassen R, Wauben LSGL, et al. Time-action and patient experience analyses of locally advanced cervical cancer brachytherapy. Brachytherapy. 2024;23(3):274-281. [2] Isensee F, Jaeger PF, Kohl SAA, et al. nnU-Net: a self-configuring method for deep learning-based biomedical image segmentation. Nat Methods. 2021;18:203-211. [3] Klein S, Staring M, Murphy K, Viergever MA, Pluim JPW. elastix: a toolbox for intensity based medical image registration. IEEE Trans Med Imaging. 2010;29(1):196-205.

2598

Digital Poster MRI-guided brachytherapy for cervical cancer - is 3 or 4 fractions best?

Clare Taylor 1 , Mary Burke 2 , Lauren Slater 1 , Lisa Barraclough 2 , Peter Hoskins 2 , Siobhan Morrison 2 , GIllian Aldred 1 , James Cummings 1 , William Gillespie 1 , Lisa Hallett 1 , Claudia Hill 1 , Rachel Joshi 1 , Niamh O'Hara 1 , Rebekah Pearce 1 , Michelle Rourke 1 , Laura Lane 1 , Kate Haslett 2 1 Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, United Kingdom. 2 Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom Purpose/Objective: Image-guided adaptive brachytherapy is the standard of care for locally advanced cervical cancer. The Royal College of Radiologists recommends the brachytherapy schedule 7.7Gy x 3 fractions (F), or 7Gy x 4F, to achieve a D90 of 85 90 Gy EQD2 to the HR-CTV [1]. Previous studies show that 3F produced comparable target and OAR doses [2]. This study aimed to find identifiable factors to determine the suitability of 3F or 4F, and to confirm outcomes. Material/Methods: Between February and September (2023), 43 patients underwent high dose-rate brachytherapy (HDR-BT), following radical chemoradiotherapy/radiotherapy. For each HDR-BT fraction, MR imaging and brachytherapy planning was performed. Delineation of targets and OARs followed the EMBRACE-II protocol [3] and international guidelines [4]. Plan doses were normalised to Point A, allowing a plan of 7.7Gy x 3F and 7Gy x 4F to be simultaneously generated. In-house software calculated the predicted final EQD2 dose to the HR-CTV and OARs, enabling the clinician to choose the optimal schedule for each patient at fraction 1. Following this decision, a brachytherapy course of 3F or 4F was delivered. Results: 33 patients (77%) received 3F of HDR-BT and 10 patients (23%) received 4F. The average HR-CTV volume was 30cm 3 (range 9-60cm 3 ) for 3F, compared to 51cm 3 (range 25-92cm 3 ) for 4F. In 41 (93%) patients, the HR-CTV D90 received at least 90 Gy EQD2. The average HR-CTV D90 for 3F was 94.5Gy EQD2 (range 87 – 99Gy), 1 patient received < 90Gy. The average HR-CTV D90 for 4F was 93Gy EQD2 (range 85 – 102Gy), 2 patients received < 90Gy. Comparing the OAR doses for 3F with 4F showed little to no significant difference. The predicted and final HR-CTV EQD2 for both 3F and 4F treatments correlated well, the average difference <1%. 91% of patients completed their treatment within 50 days. 31 patients underwent follow up at our centre. At one-year, local control was achieved in 94% patients. The 2 patients who failed to achieve local control each had 4 fractions, with HR-CTV volumes of 81cm 3 and 92cm 3 .

Conclusion: