Commissioning of a Computed tomography simulator. A single-institution experience

Based on the experience, the author explains the commissioning of CT device for radiotherapy planning and its peripherals. In radiotherapy, the CT image for planning is used for the following purposes: (1) determination of the layout of treatment beams after confirming the shape of the target or risk organ as well as the relative position of the patient with respect to the treatment device, (2) calculation of the dose distribution in the patient's body, and (3) reference image for checking the patient position during treatment. The geometrical matching between the CT slice plane and the laser alignment is to be confirmed. As for the main body of the CT device, it is recommended to display the dose length product (DLP) and volume computed tomography dose index (CTDIvol). In addition to the performance confirmation by the maker at the time of installation, the baseline (slice thickness, spatial resolution, low contrast resolution, uniformity, and noise) related to image quality is to be set. In order to prepare a conversion table to be registered to the treatment planning device that converts the HU value to relative electron concentration (physical density) against water, an electron concentration (physical density) phantom is to be used. A baseline for daily quality control is to be established, and then the position reproducibility and displacement of the couch top, roll angle and pitch angle are to be measured and confirmed. Regarding 4D-CT, this paper also explained the recognition accuracy of the respiratory cycle signal and the 4D-CT respiratory synchronization system. (A.O.)