Candidates for prostate radioactive seed implantation treated by external beam radiotherapy

We report the prostate-specific antigen-based freedom from biochemical failure after conventional and three-dimensional conformal external beam radiotherapy for patients who would have been candidates for 125I implantation monotherapy.

Patients included in the study were required to have prostate-specific antigen values < or = 20, T stage < or = 2b, and Gleason score sum of 2 to 6. All patients underwent external beam irradiation with curative intent and a minimum follow-up from completion of treatment of at least 1 year. In addition, all patients had to have pretreatment and follow-up prostate-specific antigen measurements and no history of hormonal manipulation, orchiectomy, or radical prostatectomy. A total of 187 patients meeting these criteria were treated between March 1988 and June 1995, and they form the study group for this analysis. Freedom from biochemical failure was defined as prostate-specific antigen value that failed to be maintained at 1 ng/mL or less or an increase in prostate-specific antigen value of 0.5 ng/mL or more in 1 year even if prostate-specific antigen value was less than 1 ng/mL.

Among the 187 patients, the median pretreatment prostate-specific antigen value was 7.4 ng/mL (0.3-19.9 ng/mL). The median follow-up was 34 months. Twenty-three percent of patients had a Gleason score sum of 2 to 4, and 77% had a Gleason score sum of 5 to 6. Clinical stages were T1 in 33% and T2 in 67%. One hundred twenty-five patients were treated by conventional external beam radiotherapy with a median dose of 69.5 Gy (60-71 Gy), and 62 patients were treated by three-dimensional conformal external beam radiotherapy with a median dose of 76.4 Gy (71.6-87 Gy). The overall freedom from biochemical failure was 75% at 4 years. Rates of freedom from biochemical failure by pretreatment prostate-specific antigen levels were 91% for prostate-specific antigen value < or = 4 ng/mL, 65% for prostate-specific antigen value > 4 but < or = 10 ng/mL, and 30% for prostate-specific antigen value > 10 ng/mL. Pretreatment prostate-specific antigen value was a statistically significant prognosticator, with lower values associated with favorable freedom from biochemical failure outcome in univariate and multivariate analyses. Conventional versus three-dimensional treatment, T1 versus T2 stage, and Gleason score sum 2 to 4 versus 5 to 6 did not show statistically significant difference in freedom from biochemical failure.

Although our overall results after external beam radiotherapy for early-stage prostate cancer patients are less favorable than the best results published for 125I implantation monotherapy, our results are comparable to those in most other studies with implantation monotherapy. This most likely results from selection bias as well as our stricter definition of freedom from biochemical failure. In addition, for our subset of patients, there was no statistically significant improvement in the 4-year freedom from biochemical failure with the use of higher doses.