The purpose was to evaluate the use of the CT option for simulator during a 14-month period in the radiotherapy department. The CT option has been adapted on the Philips simulator SL23. The virtual tunnel diameter is 92 cm which allows slice acquisition regardless of the contention device used. This system is connected to the treatment planning system through an Ethernet link. Three fields of view are available which cover the standard radiotherapy use. Four hundred and twenty-seven patients benefited from this system over a 14-month period of use. The number of slices acquired per patient regularly increased. The use of the system was rapidly extended to all the standard treatments. Those slices were also used as additional information for these high technology treatments. The good quality of the images and the reliability of this system involved a rapid integration in the treatment preparation procedure. It will not replace the use of the scanner but will significantly improve the treatment quality.