An investigation into the source of low energy scattered radiation of significance in film dosimetry.

The nature of the background optical density on films exposed to orthovoltage x-rays and electron beams has been studied for correction purposes. A higher than expected background value can be demonstrated by comparing the film scanned beam profile with water phantom ionisation scans of the same beam. A range of 3-5% increased background in the penumbral tail, with energy dependence, has been shown experimentally.