Dosimetric impact of inter-observer catheter reconstruction variability in ultrasound-based high-dose-rate prostate brachytherapy

Publication date: Available online 24 November 2017
Source:Brachytherapy
Author(s): Alexandru Nicolae, Jure Murgic, Ivan Kruljac, Lior Dubnitzky, Laura D'Alimonte, Lin Lu, Aaron Cumal, Niki Law, Gerard Morton, Andrew Loblaw, Hans T. Chung, Ananth Ravi
PurposeTo investigate the dosimetric impact of interobserver catheter reconstruction variability in transrectal ultrasound–guided prostate high-dose-rate (HDR) brachytherapy.Methods and MaterialsTwenty consecutive patients with intermediate- or high-risk prostate cancer were treated with a single, 15-Gy HDR brachytherapy boost as part of this study. The treated plan was used as the study reference plan (PR). Three expert treatment planners (observers) manually reconstructed the catheter paths on the static three-dimensional transrectal ultrasound images, and new plans were generated from the updated positions (POBS); subsequently, the dwell time and positions from the POBS plans were superimposed on the PR catheter paths to evaluate the dosimetric effect of the interobserver variations (PEVAL). Plans from each group were stratified by observer and by number of catheters (12 or 16) and then compared using a one-way Kruskal–Wallis H test with post hoc Mann–Whitney U tests reserved for significant variations (α = 0.05).ResultsGreater than 98.9% of catheter reconstruction variations were <3 mm. When stratified by observer, there was a significant decrease (p << 0.05) in planning target volume (PTV) V100% and increases in the urethral Dmax between the POBS plans propagated to the PR catheter paths and dosimetry evaluated and PR plans only. Stratification of plans by catheter number showed nonclinically significant decreases in PTV V100%, and D90% and increases in urethral Dmax for the 12-catheter plans.ConclusionsLimiting interobserver variability, and its effects on prostate HDR brachytherapy plan quality, is critical to achieving good dosimetric outcomes; small variations in catheter reconstruction may translate to inadequate PTV coverage, excessive urethral dose, or both.



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