Recommendation of fiducial marker implantation for better target tracking using MV imager in prostate radiotherapy

PURPOSE: The aim of this study was to develop a model that optimizes the fiducial marker locations in the prostate to increase detectability of the markers in the projected EPID images during VMAT treatments. METHODS AND MATERIALS: The fiducial marker tracking capability for each arc was evaluated through a proposed formula. The output of the formula, a detectability score, was calculated with the in-house developed software written in MATLAB (The Mathworks, Inc., Natick, MA, USA). Three unique weighting factors were added to penalize the detectability score. The detectability scores of four different patterns containing 40 combinations of simulated fiducial marker locations were evaluated with 101 previously treated prostate treatment plans (containing 202 individual arcs). The results were analyzed for each pattern group and each marker separation distance on the transverse plane. RESULTS: The maximum detectability of the markers occurred when they were placed between 10 and 15 mm from the center of the prostate in the transverse plane and 6-13 mm in the superior-inferior direction. The detectability decreased when the markers were placed beyond 20 mm in both directions. CONCLUSIONS: The fiducial marker-based detectability score can be used to predict the real-time tracking capability. Suggestions for optimal insertion locations were given to improve prostate motion management using MV imaging.