THE PHOTON BEAM CHARACTERISTICS OF LINEAR ACCELERATOR EQUIPPED WITH ADDITIONAL NARROW BEAM COLLIMATOR

In this paper a laboratory set-up with an electron linac installed in this Institute, and an attached narrow-beam col- limator for photon beam are presented. Characteristics of the circular photon beams of diameters ranging from 10 to 30 mm at the isocentre are reported. The specific quantities measured include: relative output factors, beam profiles (off axis fac- tors), and a central axis attenuation of beams. Measurements of these parameters were performed in a water phantom using small cylindrical ionisation chambers.