Equivalent uniform dose, D(90), and V(100) correlation with biochemical control after low-dose-rate prostate brachytherapy for clinically low-risk prostate cancer.

PURPOSE

To assess the correlation of postimplant dosimetric quantifiers with biochemical control of prostate cancer after low-dose-rate brachytherapy.

MATERIALS AND METHODS

Generalized equivalent uniform dose (EUD), dose in Gy to 90% of the prostate gland (D(90)), and percentage of the prostate receiving 100% of the prescribed dose (V(100)) were calculated from the postimplant dose-volume histogram (DVH) for 140 patients undergoing low-dose-rate prostate brachytherapy (LDRPB) monotherapy from 1997 to 2003 at Duke University and the Durham VA Medical Center. Biochemical recurrence was defined according to the American Society for Therapeutic Radiology and Oncology consensus definition.

RESULTS

Median followup after LDRPB was 50 months. There was a 7% biochemical recurrence rate (10/140) at last clinical followup. The median EUD was 167 Gy (range, 41-245). The median D(90) was 139 Gy (range, 45-203). The median V(100) was 88% (range, 44-100). The overall 5-year biochemical recurrence-free survival (bRFS) was 94.2%. The 5-year bRFS was 100% for EUD> or =167 Gy and 89.4% for EUD <167 Gy (p=0.008); 100% for D(90) > or =140 Gy and 90.4% for D(90) <140 Gy (p=0.020); 100% for V(100) > or =88%; and 90.3% for V(100) <88% (p=0.017). There was no statistically significant correlation between any of these factors and overall survival.

CONCLUSIONS

In our series of 140 patients with low-risk prostate cancer treated with LDRPB alone, we observed a statistically significant correlation between EUD, D(90), and V(100) and bRFS. The generalized EUD, a calculated value that incorporates the entire prostate DVH, appears to be at least as well correlated with bRFS as D(90) or V(100), and may more completely represent the totality of the dose distribution.