Why can radiation be used to control cancer?

Answer 1

Rapidly multiplying cells are more vulnerable damage from radiation. Cancer is rapidly multiplying cells. They set the dose to just above something that will kill those cells, but not enough to kill most of the rest of your cells. I've never been able to figure out why they use radiation since radiation causes cancer too. Hmmm.

Answer 2

Radiations mainly cause mutations in the cancer cells. i.e. they mutate the dna and the genes and if the gene responsible for cell division is mutated, we can easily control the fast multiplication of these cancer cells. Due to excessive exposure to such radiations, these genes do get affected or mutated and thus, cancer is controlled!
Also, the radiation therapy also affects the normal tissues to some extent but still is in use as it effectively kills the tumour causing cancer cells.

Answer 3

It kills cells -- like cancer cells.