Intensity Modulated Radiation Therapy, or IMRT, is one of the most advanced treatment methods available in external beam radiation therapy. Initially, a CT scan is performed on the affected region in order to establish the exact contours of the tumor and the surrounding healthy tissue and therefore determine the dose of radiation.
Based on this data, the radiation beam is modulated to different levels of intensity by a computer-controlled multi-leaf collimator. The "leaves" of this device periodically move in and out contouring the radiation beam to the shape of the tumor. The beams enter the body from different angles in order to maximize tumor dosage.
The IMRT technology helps to protect the adjacent healthy tissue, by only exposing it to small doses of radiation, while the tumor receives a larger, potentially more effective dose. This flux of radiation is changing throughout the area with the net affect being that the shape of radiation around the tumor is more precise with IMRT than with conventional radiation.