The use of radiochromic film for measuring the spatial distribution of the Linear Energy Transfer (LET) deposited by protons is described. The film is dosed with a proton beam and scanned to record grey-levels of the film. The grey-levels are converted to a measured dose using calibration films and the measured dose is compared to a calculated dose to generate a scaled-normalized difference (SND) between the calculated dose and the measured dose. An improved method and apparatus for treating an abnormal condition using radiation therapy in a patient in need thereof based on a measured LET is also provided.
