IMRT is a way of giving conformal radiation therapy in a targeted way
The beam strength varies across the treatment area. The tumour receives radiation from a series of small beams of different strengths.
A multi-leaf collimator is used to shape and deliver these small beams. The bars of the multi-leaf collimator are moved while the radiation is given. A crossfire technique (beams come from 2 or more directions at the same time) creates a constant dose and spares the surrounding tissues.
IMRT shapes the treatment beams very precisely and allows the dose of radiation to be adjusted for different parts of the treatment area