Purpose: We determined the 10-year biochemical and local control results for I prostate brachytherapy in men followed a minimum of 4 years.
Materials and methods: A total of 279 men with T1-T2 prostate cancer with a minimum followup of 4 years were implanted with I from 1990 to 1998 using the real-time technique. Patients were treated with the implant alone (215 or 72.5%) or with the implant and 6 months of hormone therapy (64 or 27.6%). Of the men 185 (66.3%) agreed to ultrasound guided biopsy (6 to 12 cores) a minimum of 2 years after implantation. All patients with increasing prostate specific antigen (PSA), evidence of local recurrence or a prior positive biopsy underwent repeat biopsy yearly until biopsy became negative or there was clear evidence of biochemical (PSA) progression. The radiation dose delivered to 90% of the gland (D90) was determined 30 days after implantation by computerized tomography based dosimetry. Biochemical failure was defined as 3 consecutive PSA increases. Survival curves were calculated by the Kaplan-Meier method. Cross tabulations were tested by Pearson chi-square analysis. The effect of multiple variables was tested by the log rank test (Cox regression).
Results: Median patient age was 67 years (range 42 to 82) and median followup was 6 years (range 4 to 12). Of the patients 49 (17.6%) experienced failure, for a 10-year freedom from failure (FFF) rate of 78%. Univariate analysis for 10-year FFF demonstrated that initial PSA (p = 0.001), stage (p = 0.002), risk group (p <0.001), hormone therapy (p = 0.013) and D90 (p <0.001) were significant. Multivariate analysis demonstrated that D90 (p <0.001) and risk group (p = 0.013) were the only significant variables. The RR of PSA failure was 3.0 (95% CI 2.0 to 4.4, p <0.001) and 5.6 (95% CI 3.1 to 10, p <0.001) for doses below 140 and 120 Gy, respectively. Of the 185 patients 166 (90%) had a negative post-implantation prostate biopsy. FFF was 85% vs 21% in those with a positive biopsy (p <0.001). Patients with a D90 of at least 140 Gy had a positive biopsy rate of 4.8% compared to 20.5% in those with a lower dose (p <0.001). The RR for positive biopsy at doses less than 140 and 120 Gy was 2.6 (95% CI 1.6 to 4.4, p = 0.002) and 4.3 (95% CI 2.3 to 8.1, p <0.001), respectively.
Conclusions: These data demonstrate high biochemical and local control in men with T1-T2 prostate cancer treated with I brachytherapy. The delivered radiation dose and risk category are important predictors of success. Patients receiving a dose of at least 140 Gy have a 90% chance of biochemical FFF and a 95.2% likelihood of local control.