COMPARISON OF FILM AND ION-CHAMBER SYSTEMS FOR DEPTH-DOSE MEASUREMENTS FOR A 25-MV BEAM

It is shown that the use of film with a unit density rubber phantom can produce central axis percentage depth-dose values as much as 5% larger than ion chamber/water phantom values even for a 25 MV photon beam. It is suggested that care should be taken in interpreting film generated depth-dose data for photon beams even at the highest clinical energies.