Dose to the bladder neck in MRI-guided high-dose-rate prostate brachytherapy: Impact on acute urinary toxicity and health-related quality of life.

PURPOSE: To assess the impact of the dose to the bladder neck (BN) on acute urinary toxicity (AUT) and health-related quality of life (uHRQoL) in patients with prostate cancer treated with MRI-guided high-dose-rate brachytherapy combined to external beam radiotherapy.

METHODS AND MATERIALS: Sixty-one patients were treated with a single 15-Gy MRI-guided high-dose-rate brachytherapy followed by external beam radiotherapy as part of a prospective Phase II trial. The BN was delineated in retrospect on T2-weighted images. AUT and uHRQoL data were collected prospectively using Common Terminology Criteria for Adverse Events version 4.0 and the expanded prostate index composite. A minimally important difference (MID) was defined as a deterioration of uHRQoL scores at 3 months ≥ 0.5 standard deviation of baseline score. Linear and logistic regression models were used.

RESULTS: The median BN volume was 0.6 cc. The median BN and urethral maximum dose (BNDmax and UDmax) were 22 Gy and 20 Gy, respectively. BNDmax was significantly associated with UDmax (p = 0.03). AUT Grade 2 + was observed in 32% of patients. Among those, 4 patients had an acute urinary retention (AUR). No Grade 4 + toxicity was reported. At 3 months, 47% of patients reported an MID in urinary uHRQoL. None of the dosimetric parameters including BNDmax was associated with acute Grade 2 + urinary toxicity or MID. However, 3 of 4 patients with AUR had a BNDmax in the highest quartile; >175% of prescription dose.

CONCLUSIONS: Although a high BN dose was observed in patients who had an AUR, the predictive value of this parameter is yet to be determined in a larger cohort.