Correlation between treatment plan parameters and particular prognostic factors in prostate cancer treated with high–dose–rate brachytherapy (HDR–BT) as a boost

PURPOSE: Certain constraints for target coverage and dose limits in Organs at Risk (OARs) shows some evidence that doses values and homogeneity index in treated volume depends on prognostic factors such as prostate volume, location of urethra and the number of inserted applicators. Our study is to determine the relation between values of the doses in prostate, OARs and particular prognostic factors related to HDR-BT of prostate cancer. MATERIAL AND METHODS: The amount of 190 patients with localized prostate cancer were treated with interstitial HDR-BT between July 2006 and July 2007. The HDR-BT was administered as a boost for previously delivered 50 Gy dose from external beam radiotherapy. Dose volume parameters were determined such as: D(min), D(max), D(mean), D(90), V(100), V(150) and V(200) for prostate and D(min), D(max), D(mean), D(10) and V(100) for urethra and rectum (OARs), respectively. These parameters were correlated with prognostic factors such as: age, staging (TNM), Gleason score, initial PSA level (i-PSA), number of needles and volume of the prostate. RESULTS: The mean value of D(90) was 91.3%, range 65.9-102.8%. Mean urethral D(10) was 121, 8%, range 78.8-152.9%. Mean rectal D(10) was 81.3%, range 37.4-101.0%. Statistically significant relationship was found between staging (TNM), prostate volume, and the number of needles used for implant and increased prostate D(90) and decreased V(200). The prognostic factor was only the age which was related to increased urethral D(10) and D(max). No correlation was found between any prognostic factor and rectal wall DVH parameters. CONCLUSIONS: Increased prostate volume with improved D(90) and greater number of implanted needles results in better target coverage (higher V(100)), better dose distribution (lower V(200)) and decreased dose delivered to the urethra (lower urethral D(10), D(max)), with no evident influence on rectal wall. Further investigation with closed follow-up should give an answer whether the above corresponds with morbidity and outcome.