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 control after irradiation for prostate carcinoma. An analysis of the effect of disease- and treatment-related factors on biopsy results after prostate brachytherapy was performed to aid in patient selection and treatment optimization. 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). Implants were performed using a real-time ultrasound guided technique with the isotopes (125)I in 186 and (103)Pd in 82 patients. Ninety-eight patients underwent 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 from the dose volume histogram generated using 1-month computed tomography-based dosimetry). RESULTS: Overall, 89% of patients (238 of 268) had negative biopsies. A positive biopsy was a predictor of biochemical failure. Patients with a positive biopsy had a 5-year freedom from biochemical failure of 40% versus 76% for patients with a negative biopsy (P = 0.0003). Univariate and multivariate analysis found that risk group, HT, and implant dose significantly affected biopsy outcome. Patients with low risk features (prostate specific antigen [PSA] 10 ng/mL or Gleason score >/= 7 or classification T2b or higher) (n = 164) (P = 0.008). Hormonal therapy was associated with a negative biopsy rate of 98% versus 84% for implant alone (P = 0.003). Patients receiving a high implant dose (D90 >/= 140 grays [Gy] for (125)I or >/= 100 Gy for (103)Pd) (n = 174) had a negative biopsy rate of 95% versus 77% for those receiving a low dose (D90 < 140 Gy for (125)I or < 100 Gy for (103)Pd) (n = 87; P < 0.001). CONCLUSIONS: Biopsy results support the use of brachytherapy without external beam irradiation for patients with low risk features and highlight the importance of achieving an adequate implant dose.