Purpose: To evaluate the incidence and factors predictive of acute urinary retention (AUR) in 805 consecutive patients treated with prostate brachytherapy monotherapy and to examine the possible effect of a learning curve.
Methods and materials: Between July 1998 and November 2002, 805 patients were treated with prostate brachytherapy. Low-risk patients (Gleason Score (GS) < or = 6; prostate specific antigen (PSA) < or = 10, and < or = T2b [UICC 1997]) received implant alone. Patients with prostate volume of 50 cc or more, GS = 7, or PSA = 10 to 15 received 6 months of androgen suppression (AS) with brachytherapy. Patient, treatment, and dosimetric factors examined include baseline prostate symptom score (IPSS), diabetes, vascular disease, PSA, Gleason score, clinical stage, AS, ultrasound planning target volume (PUTV), postimplant prostate volume (obtained with "Day 30" postimplant CT), CT:PUTV ratio (surrogate for postimplant edema), number of seeds, number of needles, number of seeds per needle, dosimetric parameters (V100, V150, and D90), date of implant (learning curve), and implanting oncologists. Univariate and multivariate analyses were carried out.
Results: Acute urinary retention in the first 200 patients was 17% vs. 6.3% in the most recently treated 200 patients (p = 0.002). Overall AUR was 12.7%, and prolonged urinary obstruction incidence (> 20 days) was 5%. On multivariate analysis, factors predictive of any AUR include baseline IPSS (p = < 0.004), CT:PUTV ratio (p = < 0.001), PUTV (p = < 0.001), and implant order (learning curve) (p = 0.001). Factors predictive for "prolonged" catheterization (> 20 days) on multivariate analysis include IPSS (p < 0.01), number of needles (p < 0.001), diabetes mellitus (p = 0.048), and CT:PUTV ratio (p < 0.001)
Conclusion: Over the years, our AUR rate has fallen significantly (from 17% to 6.3%). On multivariate analysis, highly significant factors include IPSS, PUTV, CT:PUTV ratio (i.e., degree of prostate edema), and order of implant (learning curve). Over the course of the program, we have deliberately reduced the number of needles and OR time per patient, which have potentially minimized intraoperative trauma and may have contributed to less toxicity. A learning curve in prostate brachytherapy programs affect not only the outcome but also the toxicity from the treatment.