(a) conventional simulator
(b) CT simulator
James C. H. Chu, PhD
Rush University Medical Center
Chicago, IL 60612
(a) A conventional simulator consists of a patient positioning couch, a rotating gantry, and associated controls. The gantry is mounted with a diagnostic x-ray source and an image intensifier. The simulator is capable of similar gantry and couch movements from a linear accelerator. This capability allows the simulator to perform a ˇ°reality checkˇ± for the treatment delivery geometry designed by a treatment planning system or from a CT simulator. The reproducibility of the patient position can be verified by diagnostic quality x-ray images; other potential patient setup problems can also be identified before the commencement of treatments. A QA program is necessary to assure that the simulator operates within the mechanical and radiation alignment tolerances expected from a linear accelerator. In addition, the performance of the imaging component requires careful evaluation. For example, the correction of image distortion from the image intensifier is necessary if the images are to be used to design the shape of treatment fields. Some of the simulators provide limited number of CT images. The accuracy of those image should also be verified if they are used for treatment planning or CT-based dose calculations.