Factors predicting for postimplantation urinary retention after permanent prostate brachytherapy.

ABSTRACT

PURPOSE: Urinary retention requiring catheterization is a known complication among prostate cancer patients treated with permanent interstitial radioactive seed implantation. However, the factors associated with this complication are not well known. This study was conducted to determine these factors. METHODS AND MATERIALS Ninety-one consecutive prostate cancer patients treated with permanent interstitial implantation at our institution from 1996 to 1999 were evaluated. All patients underwent pre-implant ultrasound and postimplant CT volume studies. Isotopes used were (125)I (54 patients) or (103)Pd (37 patients). Twenty-three patients were treated with a combination of 45 Gy of external beam radiation therapy as well as seed implantation, of which only 3 patients were treated with (125)I. Mean pretreatment prostate ultrasound volume was 35.4 cc (range, 10.0-70.2 cc). The mean planning ultrasound target volume (PUTV) was 39.6 cc (range, 16.1-74.5 cc), whereas the mean posttreatment CT target volume was 55.0 cc (range, 20.2-116 cc). Patient records were reviewed to determine which patients required urinary catheterization for relief of urinary obstruction. The following factors were analyzed as predictors for urinary retention clinical stage; Gleason score; prostate-specific antigen; external beam radiation therapy; hormone therapy; pre-implant urinary symptoms (asymptomatic/nocturia x 1 vs. more significant urinary symptoms); pretreatment ultrasound prostate volume; PUTV; PUTV within the 125%, 150%, 200%, 250%, 300% isodose lines; postimplant CT volume within the 125%, 150%, 200%, 250%, 300% isodose lines; D90; D80; D50; ratio of post-CT volume to the PUTV; the absolute change in volume between the CT volume and PUTV; number of needles used; activity per seed; and the total activity of the implant. Statistical analyses using logistic regression and chi2 were performed. RESULTS: Eleven of 91 (12%) became obstructed. Significant factors predicting for urinary retention were the total number of needles used (p < 0.038); the pretreatment ultrasound prostate volume (p < 0.048); the PUTV (p < 0.02); and the posttreatment CT volume (p < 0.021). Two of 51 patients (3.9%) requiring 33 or fewer needles (median) experienced obstruction vs. 9 of 40 (22.5%) requiring more than 33 (p < 0.007). If the pretreatment ultrasound prostate volume was 35 cc or less (median), 3 of 43 (7%) vs. 8 of 36 (22%) with a volume greater than 35 cc experienced obstruction (p < 0.051). CONCLUSION: The number of needles required (perhaps related to trauma to the prostate) and the prostate volumes were significant factors predicting for urinary retention after permanent prostate seed implantation.