Intensity Modulated Radiation Therapy (IMRT)
IMRT, or intensity modulated radiation therapy, uses 3-D scans of your body to guide the beams of radiation to the tumor from many different angles. At each of these angles, the intensity of the radiation is varied (modulated) and the shape of the beam is changed to match the shape of the tumor. These adjustments enable the prescribed amount of radiation to be delivered to each part of the tumor, while minimizing exposure to the surrounding healthy tissue. Treatments are typically given daily for 10 to 20 minutes over a six to eight week period.
IMRT is an advanced form of 3-D conformal radiation therapy that allows doctors to customize the radiation dose by modulating, or varying, the amount of radiation given to different parts of the area being treated.
The radiation beams are broken up into numerous pencil-sized beams. These smaller beams, or beamlets, can be conformed to the shape of the tumor in three dimensions. The radiation intensity is adjusted with the use of computer-controlled, moveable “leaves” which either block or allow the passage of radiation from the many beams that are aimed at the treatment area. The leaves are carefully adjusted according to the shape, size, and location of the tumor. As a result, more radiation can be delivered to the cancer while reducing damage to nearby tissue, while less is directed at the normal cells that are nearby.
An analogy for IMRT is a shower nozzle that shoots many different streams of water from different directions, except that each stream can be turned on or off, or set to deliver different intensities. This is unlike standard radiation techniques that allow only a constant flow of radiation from each beam.