Purpose To identify an anatomic structure predictive for acute (AUT) and late (LUT) urinary toxicity in patients with prostate cancer treated with low-dose-rate brachytherapy (LDR) with or without external beam radiation therapy (EBRT). Materials and Methods From 7/2002 to 1/2013, 927 patients with prostate cancer (median age, 66) underwent LDR brachytherapy using I-125 (n=753) or Pd-103 (n=174) as definitive treatment (n=478) and as a boost (n=449) followed by supplemental EBRT (median dose, 50.4 Gy). Structures contoured on Day 0 postimplant CT scan included prostate, urethra, bladder, and the bladder neck, defined as 5 mm around the urethra between the catheter balloon and the prostatic urethra. AUT and LUT were assessed using CTCAE v 4. Clinical and dosimetric factors associated with AUT and LUT were analyzed using Cox regression and receiver-operating characteristic analysis to calculate area under the receiver operator curve (ROC) (AUC). Results Grade ≥2 AUT and grade ≥2 LUT occurred in 520 (56%) patients and 154 (20%) patients, respectively. No grade 4 toxicities were observed. Bladder neck D2cc retained significant association with AUT (hazard ratio [HR], 1.03; 95% CI, 1.03–1.04) (P<.0001) and LUT (HR, 1.01; 95% CI, 1.00–1.03 (P=.014) on multivariable analysis. When comparing bladder neck with the standard dosimetric variables using ROC analysis (prostate V100>90%, D90>100%, V150>60%, urethra D20>130%), bladder neck D2cc>50% was shown to have the strongest prognostic power for AUT (AUC, 0.697; P<0.0001) and LUT (AUC, 0.620; P<.001). Conclusions Bladder neck D2cc>50% was the strongest predictor for grade ≥2 AUT and LUT in patients treated with LDR brachytherapy. These data support inclusion of bladder neck constraints into brachytherapy planning to decrease urinary toxicity.

No abstract

No abstract

No abstract