Robust tumour tracking from 2D imaging using a population-based statistical motion model

This paper describes a method for tracking a tumour using the planar projections of fiducial markers as surrogates. The projections can originate from various sources such as a beam-eye view X-ray, a portal imager or a fluoroscope. The two-dimensional position of the fiducial markers in the planar image in conjunction with a population-based statistical motion model is used to accurately predict and track the motion of a target volume during treatment. The basic assumption is that the projected surrogate locations contain valuable information about the in-plane motion of the lesion whereas the statistical motion model helps to describe the unobserved out-of-plane motion of the target volume. We analysed the accuracy with regard to varying the camera position and uncertainty in the measurement of the surrogate positions to simulate image noise and camera registration errors. The experiments showed that the tumour motion can be robustly predicted with an accuracy of 2.6 mm over a wide range of target volumes and treatment field directions despite a measurement error of σ = 2 mm for the fiducials.