Abstract
Absorbed dose conversion factors, Cλ, for several types of commercially available cylindrical chamber for photon beams with quality varying between 60Co γ rays and 20 MV X rays were calculated according to a new Japanese Association of Radiological Physicists (JARP) protocol. The new protocol C, takes account of differences between the compositions of the chamber wall and the buildup cap. For 10 MV X rays, the Cλ for NE 2581 chamber having a wall of A-150plastic and Lucentine build-up cap is different 1.2% from that for JARP chamber having a wall and buildup cap of acrylic plastics. In order to determine the consistency of the absorbed dose given according to the JARP protocol, absorbed doses were determined under the reference condition in a phantom irradiated by 60Coγ rays, and 4.2 and 8.5 MV X rays, using seven types of ionization chamber. The range of variation of the absorbed doses obtained was less than 1.1%for all investigated beam qualities. The ionization chamber readings were converted also to absorbed doses according to the American Association of Physicists in Medicine (AAPM) protocol. These absorbed doses showed good agrement, within 0.7% with absorbed doses obtained using the JARP protocols
