Question

To treat certain forms of cancer, physicians may choose to irradiate the body with high-energy radiation. Why does this therapy work?

Answer 1

I believe cancer cells are more susceptible to damage than the regular cells. 

Answer 2

High-energy radiation (such as that emitted from radioactive materials, or the UV radiation from the sun) has enough energy to form free radicals in cells' DNA.

These free radicals are extremely reactive and lead to changes in the DNA structure. Said changes may thus develop mutations and other complications in cells, causing them to die.

In other words, high-energy radiation has the property of destroying even cancerous cells, due to it affecting their molecular structure.