Intensity modulated radiation therapy (IMRT) is an advanced mode of three dimensional radiotherapy (3-D CRT) that utilizes computer controlled devices to deliver precise radiation doses to a tumor or specific areas within the tumor. With IMRT, the radiation beam can be broken up into many beamlets, and the intensity of each beamlet can be adjusted to conform more precisely to the three dimensional (3-D) shape of the tumor. Using IMRT, it may also be possible to further limit the dose of radiation that is received by normal tissues that are near the tumor. In some situations, this may also allow a higher dose of radiation to be delivered to the tumor, increasing the chance of cure.

Typically, combinations of several intensity modulated fields coming from different beam angles are used to create a custom tailored radiation plan that maximizes tumor dose and protects adjacent normal tissues.

Currently, IMRT is being used most extensively to treat cancers of the prostate, head and neck, and central nervous system. IMRT has also been used in limited situations to treat other types of cancers.

	The picture above is a prostate IMRT “map,” courtesy of Philips Medical - Radiation Oncology Systems.
	The picture above is a head and neck IMRT “map,” courtesy of Philips Medical - Radiation Oncology Systems.