Dosimetric characteristics of circular 6-MeV X-ray beams for stereotactic radiotherapy with a linear accelerator

Dosimetric characteristics of 6 MeV circular X-ray beams of diameters rangi ng from 7.5 to 35.0 mm are reported. The 6-MeV X-ray beam from Clinac 2300C D was formed using additional cylindrical BrainLAB's collimators. The mecha nical stability of the entire system was verified. Specific quantities meas ured include tissue maximum ratios (TMR), beam profiles (off-axis ratios OA R) and relative output factors. Measurements of these parameters were perfo rmed in a water phantom using small cylindrical ionization chambers and a d iamond detector. Comparison of TMR values measured with the ionization cham ber and the diamond detector showed no significant differences. It was show n that the latter yields more accurate results for beam profiles than ioniz ation chambers. The mechanical and dosimetric characteristics of this radio therapy unit are found to be suitable for stereotactic radiosurgery and rad iotherapy.