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RapidTrack: A Versatile Tool for Template-Based Target Tracking During Radiotherapy

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H Mostafavi

H Mostafavi*, A Jeung, A Sloutsky, Varian Medical Systems, Palo Alto, CA

WE-A-134-7 Wednesday 8:00AM - 9:55AM Room: 134

Purpose: To investigate the accuracy that can be obtained by using various template-based methods to track target motion from radiographic projections during radiation therapy dose delivery.

Methods: We have developed a non-clinical software suite (RapidTrack) in two parts to accomplish template-based tracking. RapidTrack-Planning is an application used to generate templates from plan CT. These templates are oriented to correspond with the imaging angle of the online images to which they will be matched. Templates may be derived from the actual voxel values of the plan CT (using MIP or tomosynthesis) or may be generated from the plan contours without reference to the voxel values. The RapidTrack-Lung application performs the actual matching with online projections using a cross-correlation method. The match locations can be used to derive a 3D position of the target. Quality of the match is measured using a peak-to-sidelobe ratio (PSR) metric, which reduces the incidence of false detection.

Results: The RapidTrack suite was shown to be quite versatile for tracking of radiotherapy targets. The generated templates are not dependent on any particular shape or structure of target; hence they are applicable to a variety of fiducial shapes as well as to fiducial-less scenarios. RapidTrack was used on intra-fraction images of seeds in pancreas; quality of the match was visually illustrated by overlaying the planning contour on the image at the match location. PSR of the match was consistently over 2.2 at all angles. Tracking of embolization coils in lung produced similar results. Breathing motion of a lung tumor was successfully tracked using a markerless algorithm based on synthetic contour template.

Conclusion: The template-based algorithm demonstrated shows promise for tracking radiotherapy targets during treatment, both in fiducial and fiducial-less scenarios. The PSR metric is an effective means of measuring the quality of tracking.

Funding Support, Disclosures, and Conflict of Interest: Varian Medical Systems

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