How Does Radiation Therapy Work

How does radiation therapy work?

Radiotherapy is a widespread treat used for cancer as seen in the radiation therapy section of this website.


Effect of radiation on cells

Radiation therapy focuses on damaging cancer cell genes DNA (DeoxyriboNucleic Acid), in order to reduce the tumor cell division rates and to induce cell death.

Generally cells are able to repair damages from some radiation exposure. If the doses of radiation are high enough, cells can be permanently damaged beyond repair. Different cells and tissues in the body tolerate radiation differently. Each part of the body can tolerate different amounts of radiation. Many areas of the body can only tolerate a certain amount of radiation in a lifetime (maximum dose).


Radiotherapy has two modes of action

A direct effect

The radiation waves will directly damage the DNA of the aimed cells.  When the cancer genes are damaged, they cannot grow and divide any more. Over time, the cells die. This means radiation can be used effectively to kill cancer cells and shrink tumors.

An indirect effect

Water molecules are not able to hold the absorbed energy of the radiation beam and as a result the molecules break, generating high reactive molecules, known as free radicals1.Those free radicals damage DNA when cells are actively dividing.


Growing and dividing

Normal cells and cancer cells divide to produce more cells. This process is called the cell cycle (see image below). The majority of normal body cells divide at a very low rate. Some cells like neurons, do not divide at all. Cancer cells and cells found in mucous membranes (mouth, intestine, rectum and vagina), in the bone marrow or in the skin, have a faster multiplication rate.

Radiation therapy is usually most effective on cells that grow and divide quickly. This makes them more vulnerable to the effects of radiation (radiosensitive).

Radiation seems to be most effective just before cell division and during cell division.

Giving radiation on a daily basis disrupts the cell cycle of cancer cells so that more of them are in the radiosensitive phase when the next dose is given.


Limited ability to repair

Cancer cells have a limited ability to repair damaged DNA. This makes them more sensitive to the effects of radiation compared to the normal body cells.

Most normal cells can repair damage and reproduce themselves between daily radiation treatments. Cancer cells are less able to do so.


Radiation therapy is a successful technique for different types of solid tumors, damaging cancer cells at the right time and repeatedly.1–6


1. Hilderley LJ (1997) Radiotherapy. In: Groenwald SL, Hansen Frogge M, Goodman M, Henke Yarbro C (eds.) Cancer Nursing Principles and Practice 4th edn. Jones and Bartlett Publishers, Boston
2. Sitton E. Early and late radiation-induced skin alterations part I: mechanisms of skin changes. Oncology Nursing Forum. 1992a;19(5):801–807
3. Tortora GJ, Grabowski SR (1996) Principles of Anatomy and Physiology 8th edn. HarperCollins, Menlo Park, California
4. Weinberg RA. How cancer arises. Scientific America 1996;275(3):62–70
5. Rice AM. An introduction to radiotherapy. Nursing Standard 1997;12(3):49–54
6. Souhami R, Tobias J (1998) Cancer and its Management 3rd edn. Blackwell Science, Oxford.

Image (below): ©Ugreen/