What kind of radiation is used in IMRT?
Currently, photons (X-rays) are used to deliver IMRT. The radiation is generated by a machine called a medical linear accelerator. This machine stands approximately nine feet tall, is nearly 15 feet long and can be rotated around the patient with great precision. Operationally, microwave energy, similar to that used in satellite television transmission, is used to accelerate electrons to nearly the speed of light. As they reach maximum speed they collide with a tungsten target, which in turn releases photons, or X-rays. Very small beams with varying intensities can be aimed at a tumor from various angles to attack the target in a complete three-dimensional manner. In fact, IMRT can be delivered with beams the size of 2.5 x 5-millimeter pixels-the size of a pencil tip-each with varying intensity. The idea is to deliver the lowest dose possible to the surrounding tissue, reducing the chance of causing a radiation side effect, while still delivering the maximum dose to the tumor.
