Analysis of dosimetric measurements in linac radiosurgery calibration

The aim of this paper is to analyse the dosimetric parameters of a linear accelerator used in radiosurgery treatments. The influence of these parameters on the resulting dose distribution are basic for delivering the predefined dose to the vascular or oncological target volume. Several dosimetric methods have been used to define the output factors for small fields. The thimble and the Markus chambers, TLD and film dosimetry are investigated; all these dosimetric systems give reliable and almost similar results if used in the correct way. In the determination of tissue maximum ratio (TMR) the response curves obtained by ionometric and film dosimetry were investigated. For TMR determination the use of the Markus chamber and the correction factors to be applied as a result of the small dimension of the field were also investigated.