What is the difference between radiation and chemotherapy?

My MIL will be having chemo for cancer. My parents and brother also had cancer and were treated with radiation. What is the difference and why would someone have one and not the other?

Radiation therapy uses high-energy radiation to shrink tumors and kill cancer cells. X-rays, gamma rays, and charged particles are types of radiation used for cancer treatment. The radiation may be delivered by a machine outside the body, or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy, also called brachytherapy). Systemic radiation therapy uses radioactive substances, such as radioactive iodine, that travel in the blood to kill cancer cells. About half of all cancer patients receive some type of radiation therapy sometime during the course of their treatment.Chemotherapy, in its most general sense, is the treatment of a disease by chemicals especially by killing micro-organisms or cancerous cells. It refers to antineoplastic drugs used to treat cancer or the combination of these drugs into a cytotoxic standardized treatment regimen. In short - Chemo kills the cancer cells with chemicals, while radiation uses high energy waves. The type of treatment your doctor chooses depends on the type of cancer you have, and the severity of the disease.

Sheena did not cite her source of where she copied the info from, but it's correct of course. Some drs, like mine, start your treatments with both at the same time and after radiation is finished, will put you on a higher dose of chemo. The chemo with radiation is given in a weaker form to make the cancer cells more sensitive to the radiation effects and stronger chemo after to kill that made it through the initial therapy. Sometime, it's radiation first to shrink tumor, then chemo to finish it off...hopefully.