Geometrical Sparing Factors for the Rectum and Bladder in the Prediction of Grade 2 and Higher Complications After High-Dose-Rate Brachytherapy for Cervical Cancer

Abstract

This study aimed to assess the predictive values of geometrical sparing factors for the rectum and bladder in high-dose-rate intracavitary brachytherapy (HDRICB) for Grade 2 and higher late sequelae in patients with cervical cancer. A total of 392 patients were enrolled in this study. They were treated with external beam radiotherapy to the pelvis, after which HDRICB was performed using Ir-192 remote after-loading at 1-week intervals for three or four sessions. The geometrical sparing factor (GSF) was defined as the average of the ratios between the reference doses and the Point A dose. A total of 46 patients (11.7%) had Grade 2 or higher late rectal complications (36 Grade 2, 9 Grade 3, and 1 Grade 4). In all, 32 patients (8.2%) had Grade 2 or higher late bladder complications (14 Grade 2, 16 Grade 3, and 2 Grade 4). Multivariate analysis demonstrated a high risk of rectal sequelae in patients who developed bladder complications (p = 0.0004, hazard ratio 3.54) and had a rectal GSF greater than 0.7 (p = 0.01, hazard ratio 1.99). The high risk factors for bladder complications were development of rectal complications (p = 0.0004, hazard ratio 3.74), concurrent chemotherapy (p = 0.0001, relative risk 3.94), and a bladder GSF greater than 0.9 (p = 0.01, hazard ratio, 2.53). This study demonstrates the predictive value of GSFs in HDRICB for cervical cancer. Patients with rectal GSFs greater than 0.7 or bladder GSFs greater than 0.9 are at risk for Grade 2 and higher late sequelae.