In vivo thermoluminescence dosimetry dose verification of transperineal 192Ir high-dose-rate brachytherapy using CT-based planning for the treatment of prostate cancer

Abstract

Purpose To evaluate the potential of in vivo thermoluminescence dosimetry to estimate the accuracy of dose delivery in conformal high-dose-rate brachytherapy of prostate cancer. Methods and materials A total of 50 LiF, TLD-100 cylindrical rods were calibrated in the dose range of interest and used as a batch for all fractions. Fourteen dosimeters for every treatment fraction were loaded in a plastic 4F catheter that was fixed in either one of the 6F needles implanted for treatment purposes or in an extra needle implanted after consulting with the patient. The 6F needles were placed either close to the urethra or in the vicinity of the median posterior wall of the prostate. Initial results are presented for 18 treatment fractions in 5 patients and compared to corresponding data calculated using the commercial treatment planning system used for the planning of the treatments based on CT images acquired postimplantation. Results The maximum observed mean difference between planned and delivered dose within a single treatment fraction was 8.57% ± 2.61% (root mean square [RMS] errors from 4.03% to 9.73%). Corresponding values obtained after averaging results over all fractions of a patient were 6.88% ± 4.93% (RMS errors from 4.82% to 7.32%). Experimental results of each fraction corresponding to the same patient point were found to agree within experimental uncertainties. Conclusions Experimental results indicate that the proposed method is feasible for dose verification purposes and suggest that dose delivery in transperineal high-dose-rate brachytherapy after CT-based planning can be of acceptable accuracy.