A coordinate transfer of anatomical information from CT to treatment simulation

Use of CT in treatment planning requires that the anatomical information obtained from the CT scans can be transferred accurately to the treatment geometry. We have developed a technique which transfers the CT data to the simulation data and vice versa. The method uses skin marks and digital radiographs reconstructed from CT scans to reproduce the patient's position. The technique has been studied with a special phantom. Based on 10 phantom set-ups, CT coordinates can be transferred to simulation coordinates with a standard deviation of 0.25 cm. This method has been applied on a number of clinical cases that involve different disease sites. For these cases, comparisons of set-up films taken at the simulator and the digital radiographs reconstructed from CT data indicate that patient position can be reproduced to within 0.5 cm.