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Validation of IBS-GEC ESTRO-ABS Computed Tomography–Based Contouring Recommendations Using Prebrachytherapy Magnetic Resonance Imaging in Patients With Cervical Cancer Treated With Definitive Radiation Therapy

Year: 2026

Type: article

Abstract: Purpose: Consensus guidelines from IBS-GEC ESTRO-ABS (Indian Brachytherapy Society- Groupe Européen de Curiethérapie - European Society for Radiotherapy and Oncology- American Brachytherapy Society) for computed tomography (CT)-based contouring have recently introduced possibilities of CT-based adaptive brachytherapy (BT) for cervical cancer. The present study attempts to validate the guidelines by using magnetic resonance imaging (MRI) at diagnosis and in a pre-BT environment. Methods and Materials: The study involved patients with stages IIB to IVA carcinoma of the cervix who had pretreatment MRI and were treated with definitive chemoradiation and hybrid-interstitial BT from April 1, 2022, to October 1, 2023. The target volumes-high-risk clinical target volume (HRCTV), intermediate-risk clinical target volume (IRCTV), and organs-at-risk that included bladder, rectum, and sigmoid-were prospectively delineated on BT planning CT using BT planning MRI for guidance, as per IBS-GEC ESTRO-ABS recommendations by a radiation oncologist. The dimensions, volumes, doses, and Dice similarity coefficient on CT were compared with those on MRI images. Results: values of <.001 and .003, respectively. There was an insignificant difference in HRCTV and IRCTV doses between CT and MR images. The median Dice similarity coefficients of HRCTV, IRCTV, bladder, rectum, and sigmoid were 0.72, 0.78, 0.76, 0.68, and 0.46, respectively. Conclusions: Despite the dimensional differences, there was no dosimetric difference in HRCTV and IRCTV. CT-based contouring using IBS-GEC ESTRO-ABS recommendations, with MRI at diagnosis and BT, similar to the MRI at diagnosis + pre-BT MRI + CT at brachytherapy environment, is safe, convenient, and addresses logistic issues in institutions, especially in low- and middle-income countries.

Source: Advances in Radiation Oncology

DOI: 10.1016/j.adro.2026.102044