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

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Abstract
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 125I in 186 and 103Pd 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; Gleason score ≤ 6; and classification 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 ≥ 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 125I or ≥ 100 Gy for 103Pd) (n = 174) had a negative biopsy rate of 95% versus 77% for those receiving a low dose (D90 < 140 Gy for 125I or < 100 Gy for 103Pd) (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. Cancer 2000;89:1829–34. © 2000 American Cancer Society.

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