Detailed urethral dosimetry in the evaluation of prostate brachytherapy-related urinary morbidity

Abstract

4712 Background: To evaluate the relationship between urinary morbidity following prostate brachytherapy and segmental urethral doses. Methods: From February 1998 through July 2002, 186 consecutive patients without a prior history of a transurethral resection underwent monotherapeutic brachytherapy (no supplemental XRT or androgen deprivation therapy) with urethral sparing techniques (average urethral dose 100–140% mPD) for clinical T1c-T2b (2002 AJCC) prostate cancer. The median follow-up was 45.5 months. Urinary morbidity was defined by time to I-PSS resolution, maximum increase in I-PSS, catheter dependency and the need for postimplant surgical intervention. An alpha blocker was initiated approximately 2 weeks prior to implantation and continued at least until the I-PSS returned to baseline. Evaluated parameters included overall urethral dose (average and maximum), doses to the base, mid-prostate, apex and urogenital diaphragm, patient age, clinical T-stage, preimplant I-PSS, ultrasound volume, isotope, D90 and V100/150/200. Results: Of the 186 patients, 176 (94.6%) had the urinary catheter permanently removed on the day of implantation with only 1 patient requiring a urinary catheter > 5 days. No patient developed a urethral stricture and only two patients (1.1%) required a postbrachytherapy TURP. For the entire cohort, I-PSS on average peaked 2 weeks following implantation with a mean time to I-PSS resolution of 14 weeks. For the entire cohort, only isotope predicted for I-PSS resolution, while neither overall average prostatic urethra nor segmental urethral dose predicted for I-PSS resolution. The maximum post-implant I-PSS increase was best predicted by preimplant I-PSS and the maximum apical urethral dose. Conclusions: Detailed urethral dosimetry did not substantially improve the ability to predict urinary morbidity. Neither the average dose to the prostatic urethra nor urethral doses stratified into base, mid-prostate, apex, and/or urogenital diaphragm segments predicted for I-PSS normalization. Radiation doses of 100–140% mPD are well tolerated by all segments of the prostatic urethra with resultant tumorcidal doses to foci of periurethral cancer. No significant financial relationships to disclose.