Radiochromic film is a type of self-developing film typically used in the testing and characterisation of radiographic equipment such as CT scanners and radiotherapy linacs. The film contains a dye which changes colour when exposed to ionising radiation, allowing the level of exposure and beam profile to be characterised.[1] Unlike x-ray film no developing process is required and results can be obtained almost instantly, while it is insensitive to visible light (making handling easier).[2]