Risk of Late Urinary Complications Following Image Guided Adaptive Brachytherapy for Locally Advanced Cervical Cancer: Refining Bladder Dose-Volume Parameters

Abstract

To study correlations between dose-volume parameters of the whole bladder and bladder trigone and late urinary toxicity in locally advanced cervical cancer patients treated with pulsed-dose-rate brachytherapy. Patients with locally advanced cervical cancer treated with chemoradiation therapy and pulsed-dose-rate brachytherapy from 2004 to 2015 were included. Cumulative dose-volume parameters of the whole bladder and bladder trigone were converted into 2-Gy/fraction equivalents (EQD2, with α/β=3Gy); these parameters, as well as clinical factors, were analyzed as predictors of toxicity in patients without local relapse. A total of 297 patients fulfilled the inclusion criteria. The median follow-up period was 4.9years (95% confidence interval 4.5-5.3years). In patients without local relapse (n = 251), the Kaplan-Meier estimated grade 2 or higher urinary toxicity rates at 3years and 5years were 25.4% and 32.1%, respectively. Minimal dose to the most exposed 2cm3 of the whole bladder [Formula: see text] , bladder International Commission on Radiation Units & Measurements (ICRU) (BICRU) dose, and trigone dose-volume parameters correlated with grade 2 or higher toxicity. At 3years, the cumulative incidence of grade 2 or higher complications was 22.8% (standard error, 2.9%) for bladder [Formula: see text] <80 GyEQD2 versus 61.8% (standard error, 12.7%) for [Formula: see text] ≥80 GyEQD2 (P=.001). In the subgroup of patients with bladder [Formula: see text] ≤80 GyEQD2, a trigone dose delivered to 50% of the volume (D50%)>60 GyEQD2 was significant for grade 2 or higher toxicity (P=.027). The probability of grade 3 or higher toxicities increased with bladder [Formula: see text] >80 GyEQD2 (16.7% vs 1.6%; hazard ratio [HR], 5.77; P=.039), BICRU dose>65 GyEQD2 (4.9% vs 1.3%; HR, 6.36; P=.018), and trigone D50%>60 GyEQD2 (3.1% vs 1.2%; HR, 6.29; P=.028). Pearson correlation coefficients showed a moderate correlation between bladder [Formula: see text] , BICRU dose, and bladder trigone D50% (P<.0001). These data suggest that [Formula: see text] ≤80 GyEQD2 should be advised for minimizing the risk of severe urinary complications (<15%). Bladder trigone dose was also predictive of severe late urinary toxicity. These constraints need further confirmation in a multicenter prospective setting.