Optimization of a newly defined target volume in fiducial marker-based dynamic tumor-tracking radiotherapy

Abstract

Background and purpose: To optimize the selection of fiducial markers used to determine the “internal target volume for tracking” (ITVtracking) for fiducial marker-based dynamic tumor-tracking (DTT) radiotherapy for lung tumors, with four-dimensional 320-row area-detector computed tomography (320-ADCT). Materials and methods: Ten patients with early-stage non-small cell lung carcinomas or metastatic lung tumors were enrolled. After implanting 4 or 5 fiducial markers around the lung tumor, all patients underwent 320-ADCT to determine the coordinates of the tumors and markers. The coordinate origin of each phase CT dataset was translated so that the marker-derived coordinate centers coincided. The ITVtracking was then defined by compositing the gross tumor volumes from all four-dimensional CT phases. We compared the ITVtracking with the typical ITV used in motion-encompassing method. We also compared the following 5 scenarios in selection of fiducial markers to define the coordinate center: a) the closest marker to the tumor, b) the closest two makers, c) the centroid of the all markers, d) the farthest two markers, and e) the farthest marker. Results: The scenario b was the best in 5 patients. The difference of the ITVtracking between the best scenario and b was less than 20% in the other 5 patients. The scenario c was the best in 4 patients. The ITVtracking was smaller than the typical ITV. Conclusion: ITVtracking was reasonable target in DTT radiotherapy. Proper ITVtracking might be created with choosing those midway between the two markers closest to the tumor or in the centroid of the markers.