The computer age has brought us a number of virtual processes. Stereotactic radiosurgery is one of the most important for brain cancer. This is a method for focusing ionizing radiation on the tumor to kill the cancerous cells, while leaving the skull intact. It is highly dependent on computer assisted imaging techniques, including magnetic resonance imaging and computed tomography, to show the surgeon the three-dimensional location, size, and shape of the tumor. The radiation is then delivered by a computer-controlled robotic system which aims the beam from many different angles to minimize damage to healthy tissue.
Commercial systems include Leksell Gamma Knife, CyberKnife, and Novalis radiosurgery. These use high intensity electromagnetic radiation classified as x-rays or gamma rays. There is no difference between x-rays and gamma rays in their effect on human tissue; the names traditionally specify the source of the radiation. X-rays are produced by electronic processes, whereas gamma rays are produced by nuclear processes. Cobalt-60 is a radioactive isotope commonly used to produce ionizing radiation. All forms of ionizing radiation damage normal cells also, but cancer cells can be more sensitive to radiation because they are rapidly dividing.
Charged particle beam therapy has the same effects as high-energy electromagnetic radiation, but it offers the promise of more specific targeting. Electromagnetic radiation deposits energy all along its path. It's easy to see this in a microwave oven, which uses low-frequency electromagnetic radiation that is able to heat materials but unable to produce chemical reactions. When you cook a potato in the microwave oven, the heating effect starts at the surface and works its way in. Charged particle (usually proton) beams can deposit their energy at the end of their range. Under ideal conditions, this is like heating up a small spot in the center of the potato while leaving the rest of it cool.