Dosimetric aspects of the therapeutic photon beams from a dual-energy linear accelerator.

Parameters of the photon beams (6 and 20 MV) from a dual-energy linear accelerator (Mevatron-KD, Siemens Medical Laboratories, CA) are presented. The depth dose characteristics of the photon beams are dmax of 1.8 and 3.8 cm and percentage depth dose of 68% and 80% at 10-cm depth and 100-cm source-surface distance for a field size of 10 X 10 cm2 for 6 and 20 MV, respectively. The 6 and 20 MV beams were found to correspond to nominal accelerating potentials of 4.7 and 17 MV, respectively. The stability of output is within +/- 1% and flatness and symmetry are within +/- 3%. These figures compare favorably with the manufacturer's specifications.