Analysis of the Cancer of the Prostate Risk Assessment to Predict for Biochemical Failure After External Beam Radiotherapy or Prostate Seed Brachytherapy

Abstract

To analyze the value of the Cancer of the Prostate Risk Assessment (CAPRA) score to predict biochemical failure (bF) in patients with D'Amico low- or intermediate-risk prostate cancer treated with different radiation techniques. We analyzed 744 patients treated with either external beam radiotherapy (52.7%) or permanent-seed prostate brachytherapy (47.3%) without any androgen deprivation. External beam radiotherapy dose levels were extreme hypofractionation (45 Gy in 9 fractions) in 10%, 76-79.2 Gy (in 1.8-2.0 Gy per fraction) in 32.7%, and 70.2-74 Gy in 10%. All patients had a minimum of 36-month follow-up. Cox regression analysis was used for univariate and multivariate analysis to predict for bF, as per the Phoenix definition (prostate-specific antigen-nadir + 2 ng/mL). Median follow-up for patients without bF was 56 months (range, 36-114 months). In univariate analysis, CAPRA score as a continuous variable was predictive of bF (hazard ratio [HR], 1.49; 95% confidence interval [CI], 1.23-1.79; P <.001), and in multivariate analysis adjusted for treatment type, the HR was 1.39 (95% CI, 1.14-1.71; P = .002). D'Amico intermediate-risk vs low-risk patients had an HR for bF of 1.93 (95% CI, 1.07-3.47; P = .029) in univariate analysis, but the difference was not statistically significant anymore after adjustment for treatment type, (P = .206). The area under the curve of the CAPRA score as a continuous variable at 3 and 5 years was 0.66 and 0.62, respectively (P = .005 for both years). The CAPRA score is predictive of bF. Each 1-point rise increased the risk of bF by 39%, which is comparable to surgical series.