According to MayoClinic.com, radiation therapy employs high-powered energy such as X-rays to kill cancer cells.

Chemotherapy

It's important to understand the distinction between radiation and chemotherapy, as many patients and their family members get the two terms confused. WebMD.com notes that chemotherapy uses drugs to kill cancer cells, instead of radiation. The two may be used in conjunction with one another, which is perhaps why the terminology gets confusing for patients.