The effect of disease and treatment-related factors on biopsy results after prostate brachytherapy - Implications for treatment optimization

BACKGROUND. Posttreatment prostate biopsy is a method of assessing local co ntrol after irradiation for prostate carcinoma. An analysis of the effect o f disease- and treatment-related factors on biopsy results after prostate b rachytherapy was performed to aid in patient selection and treatment optimi zation. METHODS, Two hundred sixty-eight patients underwent posttreatment prostate biopsy (6-8 cores) 2 years after brachytherapy alone without external beam irradiation. Follow-up ranged from 24 to 111 months (median, 43 months). Im plants were performed using a real-time ultrasound guided technique with th e isotopes I-125 in 186 and Pd-103 in 82 patients. Ninety-eight patients un derwent hormonal therapy (HT) 3 months before and 2-3 months after implant. Implant dose was defined as the D90 (dose delivered to 90% of the gland fr om the dose volume histogram generated using 1-month computed tomography-ba sed dosimetry). RESULTS. Overall, 89% of patients (238 of 268) had negative biopsies. A pos itive biopsy was a predictor of biochemical failure. Patients with a positi ve biopsy had a 5-year freedom from biochemical failure of 40% versus 76% f or patients with a negative biopsy (P = 0.0003). Univariate and multivariat e analysis found that risk group, HT, and implant dose significantly affect ed biopsy outcome. Patients with low risk features (prostate specific antig en [PSA] less than or equal to 10 ng/mL; Gleason score 6; and classificatio n T2a or lower) (n = 104) had a negative biopsy rate of 95% versus 85% For those with high risk features (PSA > 10 ng/mL or Gleason score greater than or equal to 7 or classification T2b or higher) (n = 164) (P = 0.008). Horm onal therapy was associated with a negative biopsy rate of 98% versus 84% f or implant alone (P = 0.003). Patients receiving a high implant dose (D90 g reater than or equal to 140 grays [Gy] for I-125 or greater than or equal t o 100 Gy for Pd-103) (n = 174) had a negative biopsy rate of 95% versus 77% for those receiving a low dose (D90 < 140 Gy for I-125 or < 100 Gy for Pd- 103) (n = 87; P < 0.001). CONCLUSIONS. Biopsy results support the use of brachytherapy without extern al bean. irradiation for patients with low risk features and highlight the importance of achieving an adequate implant dose. Cancer 2000;89:1829-34. ( C) 2000 American Cancer Society.