Automated target tracking in kilovoltage images using dynamic templates of fiducial marker clusters

摘要

Purpose: Implanted fiducial markers are often used in radiotherapy tofacilitate accurate visualization and localization of tumors. Typically, suchmarkers are used to aid daily patient positioning and to verify the target'sposition during treatment. This work introduces a novel, automated method foridentifying fiducial markers in planar x-ray imaging. Methods: In brief, the method consists of automated filtration andreconstruction steps that generate 3D templates of marker positions. Thenormalized cross-correlation was the used to identify fiducial markers inprojection images. To quantify the accuracy of the technique, a phantom studywas performed. 75 pre-treatment CBCT scans of 15 pancreatic cancer patientswere analyzed to test the automated technique under real life conditions,including several challenging scenarios for tracking fiducial markers. Results: In phantom and patient studies, the method automatically trackedvisible marker clusters in 100% of projection images. For scans in which aphantom exhibited 0D, 1D, and 3D motion, the automated technique showed medianerrors of 39 $\mu$m, 53 $\mu$m, and 93 $\mu$m, respectively. Human precisionwas worse in comparison. Automated tracking was performed accurately despitethe presence of other metallic objects. Additionally, transient differences inthe cross-correlation score identified instances where markers disappeared fromview. Conclusions: A novel, automated method for producing dynamic templates offiducial marker clusters has been developed. Production of these templatesautomatically provides measurements of tumor motion that occurred during theCBCT scan that was used to produce them. Additionally, using these templateswith intra-fractional images could potentially allow for more robust real-timetarget tracking in radiotherapy.