How Radiation Can Treat Cancer
When radiation penetrates the body, it damages cellular DNA. This happens to both cancer cells and healthy cells, but since the cancer cells are not as good at recovering from the damage as the healthy cells, they are more affected by the radiation, and die.
Radiotherapy uses this property to beam only as much radiation into the cells as the healthy ones can recover from each day, doing this for many days to reduce the damage to the healthy cells while killing off the cancer cells.
In proton therapy, the radiation reaches its maximum strength at a certain distance, and does not penetrate any further than that. That means that, compared to X-ray therapy, radiation can be focused on the cancer cells and minimize the effects on the healthy cells.