Intermediate term biochemical-free progression and local control following 125iodine brachytherapy for prostate cancer.

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.