[A quality assurance program of simulators in radiation therapy. 2. Extent and results of long-term quality assurance test on a therapy simulator].

Background: Since 1990 we follow a quality assurance program with periodical tests of functional performance values of a 16-year-old simulator.

Material And Method: For this purpose we adopted and modified German standards for quality assurance on linear accelerators and international standards elaborated for simulators (International Electrotechnical Commission). The tests are subdivided into daily visual checks (light field indication, optical distance indicator, isocentre-indicating devices, indication of gantry and collimator angles) and monthly and annually tests of relevant simulator parameters. Some important examples demonstrate the small variation of parameters over 6 years: position of the light field centre when rotating the collimator, diameter of the isocentre circle when rotating the gantry, accuracy of the isocentre indication device, and coincidence of light field and simulated radiation field.

Results: As an important result we can state, that by these rigid periodic tests it was possible to detect and compensate deteriorations of simulators quality rapidly.

Conclusions: Technical improvements and specific calling-in of maintenance personnel whenever felt appropriate provided performance characteristics of our old simulator which are required by international recommendations as a basis for modern radiotherapy.