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 d max 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 10×10 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.