How a Linear Accelerator Works - HD
Looking for images of linear accelerators, I stumbled over this video. First time I have seen a linear accelerator used for any practical application, and the first time I have seen one this small. Usually I expect to them to be big machines buried in some obscure basement of a university physics department building. They are certainly going to a lot of trouble to produce X-rays, but I imagine there are reasons for that, like higher power and more control.
The whole thing about using radiation for cancer treatment is that the mutant cells, which is what cancer cells are, are not so good at repairing any damage they incur, so a good dose of radiation will damage them enough so they will die. Healthy cells can repair a small amount of radiation damage, so the trick is to administer enough radiation that the tumor is damaged enough to kill it, but healthy tissue is able to recover.