Poster — Thur Eve — 11: Evaluation of the Performance of a Positron Emission Based Tumour‐Tracking Technique

The delivery accuracy of radiotherapy treatments remains limited by tumor motion due to patient breathing. We present a simulation study and experimental evaluation of a technique called PeTrack that can track tumour location in real‐time. Position sensitive detectors record annihilation coincidence events from fiducial positron emission markers implanted in or around the tumour. It uses an expectation‐maximization clustering algorithm to track the position of the markers and a linear extrapolation method for motion prediction. We assessed the performance of the tracking using a clinical positron emission tomography system with the markers moving in different patterns. We also evaluated the performance of the tracking for stationary markers using a prototype PeTrack detector. In the experimental study with the PET scanner, the data was fitted to two theoretical curves. The root mean square error (RMSE) was 0.43 mm in x and 0.46 mm in y for a sinusoidal movement pattern. The RMSE was 0.64 mm in x for motion following animal breathing data. The linear extrapolation method for motion prediction yielded an average prediction error of 1.1 mm in the experimental study, with a prediction error of 2.3 mm at a 95% confidence level. Using the prototype PeTrack detector, the tracking precision was found to be 0.16 mm in x, 0.20 mm in y and 0.21 mm in z. We conclude that PeTrack can track tumour motion in real‐time and improve the delivery accuracy of radiotherapy.