IMRT is a new and special form of radiation therapy in which irregular radiation intensities are generated by radiating a large number of small fields with beams from as many different directions as possible. When these different intensities are superimposed in three dimensions, they produce a dose distribution which conforms as closely as possible to the tumour.

IMRT enables the dose to be escalated in areas at particular risk of tumour recurrence while providing better protection for the healthy tissue surrounding the tumour. In short, IMRT combines greater efficacy against tumours with a lower rate of side effects. This technique is used particularly for radiotherapy of head and neck tumours and prostate cancer. In future it may be extended to gastrointestinal and gynaecological tumours.