Lack of the Dose-Rate Effect of ¹⁹²Ir Source Activity on Pelvic Control and Late Complications After High-Dose-Rate Brachytherapy for Cervical Cancer

Abstract

This study aimed to assess the dose-rate effect of ¹⁹²Ir source activity on pelvic control and late complications following high-dose-rate intracavitary brachytherapy (HDRICB) for cervical cancer patients. Two hundred and twelve patients were enrolled in this study. They were treated with external beam radiotherapy to the pelvis, after which HDRICB was performed using ¹⁹²Ir remote after-loading at 1-week intervals for 4 or 5 sessions. Source activity was defined as the average of source activity in each HDRICB session. Dose-rate effect was analyzed after stratification of stage and biologically effective dose (BED). The 5-year pelvic relapse-free survival was 88% for all patients. Forty-two patients developed late rectal complications (13 grade 1, 23 grade 2, 6 grade 3–4). Twenty-seven patients had grade 2 and higher late bladder complications (14 grade 2, 13 grade 3–4). There was no dose-rate effect on pelvic control or complications when source activity was stratified. Multivariate analysis demonstrated a high risk of grade 2 and higher rectal sequelae in patients whose rectal BED ≥ 110 Gy₃ (p = 0.039, hazard ratio 2.05). The high risk factors for grade 2 and higher bladder complications were a bladder BED ≥ 100 Gy₃ (p = 0.03, hazard ratio 4.37). This study demonstrated no dose-rate effect of ¹⁹²Ir source in HDRICB for cervical cancer in terms of pelvic control or radiation injuries. Careful monitoring of the BED values for rectum and bladder is a scrutinizing factor for minimizing late sequelae.