What Is the Difference between Chemotherapy and Radiation Therapy?

Chemotherapy and radiation therapy are two ways of treating cancer that destroy cancer cells by damaging their DNA. Although both chemotherapy and radiation therapy are effective cancer treatments, they are used in different situations and have different side effects. Chemotherapy is used to treat cancer throughout the body by using drugs injected into the bloodstream, whereas radiation therapy can target tumors located in specific areas of the body. Chemotherapy and radiation therapy can be used to treat the same cancer, or just one of these treatments might be used, depending on the type of cancer and the extent of its progression. For example, a localized tumor from prostate cancer might require only radiation treatment, and just chemotherapy might be used to treat leukemia, but both chemotherapy and radiation therapy could be used to treat a tumor that has metastasized.

Chemotherapy involves the use of drugs that usually target cells while they replicate their DNA. Cancer cells replicate more rapidly than healthy cells, so attacking cells that are in the process of replication is one way to kill cancer cells while harming as few healthy cells as possible. Chemotherapy is often applied in cycles, utilizing different drugs, so that the maximum number of cancer cells can be killed, while attempting to give healthy tissue a chance to recover from the drugs’ effects. The side effects of chemotherapy are caused by the drugs inadvertently killing these healthy cells, such as those in bone marrow, which produce white and red blood cells; cells in the stomach and intestines; and hair follicle cells. When these tissues are damaged, they can lead to a weakened immune system, anemia, nausea, vomiting and hair loss.

Radiation therapy is a procedure that uses X-rays, gamma rays, and radioactive particles to target tumors arising from localized cancers. This form of treatment often uses machines to direct high-frequency radioactive waves toward tumors, or it might involve small amounts of radioactive substances injected near the cancerous cells. After the radiation is inside of these cells, it forms free radicals to damage DNA or directly change the structure of their DNA; either way, the result is that cells whose DNA is sufficiently damaged have their replication process disrupted and die. Using radiation therapy causes damage to nearby healthy tissue, especially to cells that divide rapidly. The side effects of radiation therapy usually involve skin irritation and scarring; possible hair loss, urinary problems or stomach problems, depending on the site of treatment; as well as possible long-term side effects such as fibrosis, amnesia and fertility issues.