Purpose: To study the effect on biochemical relapse-free survival (bRFS) and clinical disease-free survival of radiation doses delivered to the prostate and periprostatic tissues for localized prostate cancer.
Methods and materials: A total of 1041 consecutive localized prostate cancer cases treated with external beam radiotherapy (RT) at our institution between 7/86 and 2/99 were reviewed. All cases had available pretreatment parameters including pretreatment prostate-specific antigen (iPSA), biopsy Gleason score (bGS), and clinical T stage. The median age was 69 years. Twenty-three percent of cases (n = 238) were African-American. The distribution by clinical T stage was as follows: T1 in 365 cases (35%), T2 in 562 cases (54%), and T3 in 114 cases (11%). The median iPSA level was 10.1 ng/ml (range: 0.4-692.9). The distribution by biopsy Gleason score (bGS) was as follows: < or =6 in 580 cases (56%) and > or =7 in 461 cases (44%). Androgen deprivation (AD) in the adjuvant or neoadjuvant setting was given in 303 cases (29%). The mean RT dose was 71.9 Gy (range: 57.6-78.0 Gy). The median RT dose was 70.2 Gy, with 458 cases (44%) receiving at least 72.0 Gy. The average dose in patients receiving <72 Gy was 68.3 Gy (median 68.4) versus 76.5 Gy (median 78.0) for patients receiving > or =72 Gy. The mean follow-up was 38 months (median 33 months). The number of follow-up prostate-specific antigen (PSA) levels available was 5998.
Results: The 5- and 8-year bRFS rates were 61% (95% CI 55-65%) and 58% (95% CI 51-65%), respectively. The 5-year bRFS rates for patients receiving radiation doses > or =72 Gy versus <72 Gy were 87% (95% CI 82-92%) and 55% (95% CI 49-60%), respectively. The 8-year bRFS rates for patients receiving radiation doses > or =72 Gy versus <72 Gy were 87% (95% CI 82-92%) and 51% (95% CI 44-58%), respectively (p < 0.001). A multivariate analysis of factors affecting bRFS was performed using the following parameters: age (continuous variable), race, T-stage (T1-T2 vs. T3), iPSA (continuous variable), bGS (< or =6 vs. > or =7), use of AD (yes vs. no), radiation technique (conformal versus standard), and radiation dose (continuous variable). T-stage (p < 0.001), iPSA (p < 0.001), bGS (p < 0.001), and RT dose (p < 0.001) were independent predictors of outcome. Age (p = 0.74), race (p = 0.96), radiation technique (p = 0.15), and use of AD (p = 0.31) were not. We observed 11% clinical failures (local, distant, or both) at 5 years and 15% at 8 years for the entire cohort. There was a statistically significant improvement with higher radiation doses (p = 0.032). The 5-year clinical relapse rates for patients receiving > or =72 Gy versus <72 Gy were 5% and 12%, respectively. The 8-year clinical relapse rates for patients receiving radiation doses > or =72 Gy versus <72 Gy were 5% and 17%, respectively (p = 0.026).
Conclusion: Patients receiving radiation doses exceeding 72 Gy had significantly better bRFS and clinical disease-free survival rates. Although results need to be confirmed with longer follow-up, these preliminary results are extremely encouraging. If these results are confirmed by other institutions and by longer follow-up, RT doses exceeding 72 Gy should be considered as standard of care.