Cancer cells multiply faster than normal cells in the body. Because radiation is most harmful to quickly growing cells, radiation therapy damages cancer cells more than normal cells. This prevents the cancer cells from growing and dividing, and leads to cell death.

Radiation therapy is used to fight many types of cancer and to treat some benign diseases. Sometimes, radiation is the only treatment needed. It may also be used in combination with other therapies such as surgery or chemotherapy to:

• Shrink a tumor as much as possible before surgery
• Help prevent the cancer from coming back after surgery or chemotherapy
• Relieve symptoms caused by a tumor, such as pain, pressure, or bleeding
• Treat cancers that cannot be removed with surgery
• Treat cancers instead of using surgery

TYPES OF RADIATION THERAPY

Different types of radiation therapy include external, internal, and intraoperative.

EXTERNAL RADIATION THERAPY

External radiation is the most common form. This method carefully aims high-powered radiation or particles directly at the tumor from outside of the body. Newer methods provide more effective treatment with less tissue damage. These include:

• Intensity-modulated radiotherapy (IMRT)
• 3D Conformal Radiotherapy (3DCRT)
• Electron Beam Therapy
• Image-guided radiotherapy (IGRT)
• Stereotactic radiotherapy (radiosurgery)

Proton therapy is another kind of radiation used to treat cancer. Rather than using radiation to destroy cancer cells, proton therapy uses a beam of special particles called protons. Because it causes less damage to healthy tissue, proton therapy is often used for cancers that are very close to critical parts of the body. It is only used for certain types of cancer.

INTERNAL RADIATION THERAPY

Internal beam radiation is placed inside your body.

• One method uses radioactive seeds that are placed directly into or near the tumor. This method is called brachytherapy, and is used to treat prostate cancer. It is used less often to treat breast, cervical, lung, skin, and other cancers.
• Another method involves receiving a specific radioactive liquid that emits radiation, called a radio nucleotide. This liquid radiation can be given in a drink with a pill, or through an IV. Liquid radiation travels throughout your body, seeking out and killing cancer cells. Thyroid cancer and some metastatic cancers such as prostate can be treated using liquid radiation.

INTRAOPERTIVE RADIATION THERAPY (IORT)

This type of radiation is usually used during surgery to remove a tumor. Right after the tumor is removed and before the surgeon closes the incision, radiation is delivered to the site where the tumor used to be. IORT is generally used for tumors that have not spread and microscopic tumor cells may remain after the larger tumor is removed.

Compared with external radiation, advantages of IORT may include:

• Only the tumor area is targeted so there is less harm to healthy tissue
• Only a single dose of radiation is given
• Delivers a smaller dose of radiation

SIDE EFFECTS OF RADIATION THERAPY

Radiation therapy can also damage or kill healthy cells. The death of healthy cells can lead to side effects.

These side effects depend on the dose of radiation, and how often you have the therapy. External beam radiation may cause skin changes, such as hair loss, red or burning skin, thinning of skin tissue, or even shedding of the outer layer of skin.

Other side effects depend on the part of the body receiving radiation:

• Abdomen
• Brain
• Breast
• Chest
• Mouth and neck
• Pelvic (between the hips)
• Prostate

Radiotherapy; Cancer - radiation therapy; Radiation therapy - radioactive seeds; Intensity-modulated radiotherapy (IMRT); Image-guided radiotherapy (IGRT); Radiosurgery-radiation therapy; Stereotactic radiotherapy (SRT)-radiation therapy; Stereotactic body radiotherapy (SBRT)-radiation therapy; Intraoperative radiotherapy; Proton radiotherapy-radiation therapy; Radionucleotides; Radioisotopes

Czito BG, Calvo FA, Haddock MG, Blitzlau R, Willett CG. Intraoperative irradiation. In: Gunderson LL, Tepper JE, eds. Gunderson and Tepper's Clinical Radiation Oncology. 5th ed. Philadelphia, PA: Elsevier; 2021:chap 22.

Doroshow JH. Approach to the patient with cancer. In: Goldman L, Cooney K, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 164.

National Cancer Institute website. Radiation therapy to treat cancer. www.cancer.gov/about-cancer/treatment/types/radiation-therapy. Updated January 8, 2019. Accessed June 18, 2024.

Zeman EM, Schreiber EC, Tepper JE. Basics of radiation therapy. In: Niederhuber JE, Armitage JO, Kastan MB, Doroshow JH, Tepper JE, eds. Abeloff's Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:chap 27.

Updated by: David Herold, MD, Radiation Oncologist in Jupiter, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.