Purpose: To develop a tracking algorithm for linear positron emission marker for external beam radiation therapy. Method and Materials: The delivery accuracy of external beam radiation therapy is currently limited by the motion of tumour during treatment. By implanting positron emission fiducial markers into the tumor, and using pairs of position‐sensitive detectors to track the resulting annihilation gamma rays, the position of the tumor can be tracked in real‐time with high accuracy. Positron emission based technique will deliver a lower radiation dose to normal tissue than x‐ray fluoroscopy, and the smaller size of the positron emission markers reduces risk to the patient during implantation. Some previous studies have shown that multiple point markers can be tracked using this technique. In this study, we further extended the technique to track a linear marker. Using a single linear marker has many advantages as compared with multiple point markers: single implantation instead of three can further reduce the patient risk and totally eliminates the possibility of marker migration. An algorithm that iteratively estimates the location and orientation of the linear marker is proposed. The algorithm was then evaluated using data obtained from Monte Carlo simulation. Results: The accuracy of the tracking algorithm improves with increased number of events used. The center of the linear marker was localized to sub‐millimeter accuracy with a total of 1000 events. The end‐points of linear marker were localized with average accuracy of about 2.5 mm, which converts to about 6 degree of uncertainty on the orientation. Conclusion: Linear fiducial marker labeled with positron emission isotope can be localized with sub‐millimeter accuracy and can be potentially used for real‐time tumour tracking during radiation therapy.

Medical Physics
Department of Physics

Xu, T, Churchill, N., & Chamberland, M. (2008). SU‐GG‐J‐150: Positron Emission Based Technique for Linear Fiducial Marker Tracking During Radiation Therapy. In Medical Physics (Vol. 35). doi:10.1118/1.2961699