Dosimetric Comparison between Treatment Plans of Patients Treated with Low-Dose-Rate Versus High-Dose-Rate Interstitial Prostate Brachytherapy as Monotherapy: Initial Findings of a Randomized Clinical Trial

Abstract

To assess and compare the dosimetry of intraoperative dose plans of prostate cancer patients treated with low-dose rate and high-dose rate interstitial brachytherapy. A randomized clinical trial was initiated at our institution to compare the results and side effects of low-dose-rate (LDR) and high-dose-rate (HDR) brachytherapy (BT) as monotherapy in the treatment of early, organ confined prostate cancer patients. Fifty patients with low and selected intermediate risk prostate cancer were randomly assigned to receive HDR afterloading BT with one fraction of 19 Gy or permanent LDR I-125 seed BT with 145 Gy. In both techniques the implantation was performed with transrectal ultrasound guidance in spinal anesthesia, and intraoperative dose plans were made on ultrasound images using inverse optimization algorithms (IPSA for LDR and HIPO for HDR). Dose-volume constraints for prostate, urethra and rectum were applied during optimization. Stranded seeds were implanted into the prostate using live ultrasound imaging following preimplant treatment planning. The HDR treatments were performed after preimplant planning, but final dosimetry was based on updated needle and contour positions. Treatment plans were compared using dose-volume histograms, dose coverage metrics including V100, V150, conformal index (COIN) and dose homogeneity index (DHI) for prostate. Dose to urethra was characterized by D10, D30, D0.1cc and D0.01cc. Dose to rectum was described by D2cc, D1cc, D0.1cc, D0.01cc and D10. Statistical comparisons with non-parametric test were performed between the corresponding parameters. The median needle number was 20 and 18 for LDR and HDR treatments, respectively. The mean seed number was 46.The total seed activity was 26.8 mCi with individual median seed activity of 0.562 mCi. The target coverage by the prescribed dose was larger than 95% for both patient groups, and the V100 was higher for LDR patients. The other parameters are shown in the table.To make the comparison more easy dose parameters are given in relative values, in percentages related to prescribed dose. Except for volume of the prostate the difference between the means of all other parameters for the two patient groups was statistically significant (p<0.05). Both techniques provided acceptable target volume coverage, but higher percentage of target volume was irradiated by the prescribed dose with LDR technique. The dose distributions were more homogeneous with HDR technique, and both urethra and rectum received less relative dose in patients treated with HDR technique. To assess whether these dosimetric data translate in differences in clinical outcomes more patient data and longer follow-up are needed.Tabled 1ProstateV (ccm)V100V150DHICOINLDR32.299620.370.64HDR35.497300.700.80UrethraV (cc)D10D30D0.1ccD0.01ccLDR1.4135129136.0146.9HDR1.6113110113.1115.3RectumD2ccD1ccD0.1ccD0.01ccD10LDR67.179.098.4111.288HDR54.762.875.781.067 Open table in a new tab