Impact of transrectal ultrasound- and computed tomography-based seed localization on postimplant dosimetry in prostate brachytherapy

Abstract

PurposeTo study the impact of seed localization, as performed by different observers using linked 125I seeds, on postimplant dosimetry in prostate brachytherapy and, to compare transrectal ultrasound (TRUS)-based with CT-based approach for the dosimetric outcomes. Methods and MaterialsNineteen permanent prostate implants were conducted using linked 125I seeds. Postimplant TRUS and CT images were acquired and prostate glands were, after implantation, delineated on all images by a single oncologist, who had performed all 19 seeding procedures. Six observers independently localized the seeds on both TRUS and CT images, from which the principle dosimetric parameters V100 (volume of prostate that received the prescribed dose), V150 (volume of prostate that received 150% of the prescribed dose), and D90 (minimal dose delivered to 90% of the prostate) were directly calculated for each patient. A single-factor analysis of variance was first applied to determine interobserver variability in seed localization. A nonparametric comparison of the approach using TRUS and CT was then carried out by the Wilcoxon paired-sample test. ResultsAnalysis from the analysis of variance for TRUS showed that the null hypothesis for equal means, could not be rejected for all six observers based on a significance level α=0.05. TRUS-based and CT-based approaches were then cross compared by the Wilcoxon paired-sample test, which suggested that the null hypothesis was insignificant for V100 and D90, but was significant for V150. ConclusionsBoth TRUS- and CT-imaging modalities provided indistinguishable postimplant dosimetry results as far as V100 and D90 were concerned. There was comparable observer independence between TRUS- and CT-based seed localization for linked-seed implant procedures. With other advantages that TRUS-imaging modality had over CT in the evaluation of postimplant dosimetry, TRUS would be a preferred choice in conjunction with linked seeds for intraoperative procedures in prostate brachytherapy.