THE INFLUENCE OF THE MAGNETRON FREQUENCY, THE SERVO SETTINGS AND THE GANTRY ANGLE ON THE FLATNESS AND THE DOSE CALIBRATION OF A LINEAR-ACCELERATOR

For the Philips SL75/5, we have noticed that the performance of the be am (e.g. the hump) varies with the settings of the magnetron frequency and the gantry angle. This study investigated these changes and the o ptimum magnetron frequency setting was determined. The relation betwee n the relative absorbed dose measured by the accelerator and the relat ive absorbed dose measured for different amounts of the hump in the ce ntre of the beam was found. Results from a model and from measured val ues were compared. The beam was studied for different gantry angles an d for different adjustments of the beam servo systems. The profiles ob tained showed some variations, but were reduced when optimal adjustmen ts of the servos were performed.