Real-time Tumor Tracking for Pencil Beam Scanning Proton Therapy

In this paper, we describe the method and implementation of a real-time tumor tracking system for a pencil beam scanning (PBS) proton therapy system. PBS is an advanced cancer treatment system that can benefit from precise localization of the tumors through motion. We utilize techniques such as cross-correlation matching, correlation filters and small object saliency, creating an array of methods that can detect and track fiducial markers implanted in the cancer tumors. The final aim is to control the proton beam using real-time image guidance. Our technique works robustly on various types of markers such as ceramic/ metallic fiducials, visicoil markers and surgical clips. Left and right views of an X-ray fluoroscopy system were utilized to also triangulate the marker positions in full 3D as they are tracked through normal breathing movement and organ motion. We have tested our detection system on data from several patients with different tumor locations both offline and in real-time and wish to implement it within a full treatment system soon. To the best of the authors knowledge, this is the first real time tracking system for PBS therapy that is applicable for various types of fiducials and tumor locations.