External Beam Radiation Therapy

Radiation therapy (sometimes referred to as radiotherapy, x-ray therapy or irradiation) has been used to treat for many types of cancer for more than 100 years. Radiation therapy refers to the careful use of various forms of radiation to treat cancer. The physicians who specialize in radiation therapy are radiation oncologists.

Radiation therapy works by damaging the DNA (the control center) of cancer cells, destroying the ability of the cancer cells to divide, which can kill cancer cells and shrink the tumor. When these damaged cancer cells die, the body naturally eliminates them. Normal cells may also be affected by radiation, but they can repair themselves in a way that cancer cells cannot.

Prior to radiation therapy, a simulation is conducted at which point a CT scan is usually done to help in the development of a radiation plan. A computer is used to help design the best radiation treatment plan. After reviewing this information, the radiation oncologist decides the exact course of radiation therapy.

A machine referred to as a linear accelerator is used to direct high-energy rays at the cancer, delivered through the skin. The linear accelerator is located outside the body and does not touch the skin. Receiving external beam radiation is similar to having a CT scan. It is painless. It is usually given as a series of daily outpatient procedures, but can be delivered in one treatment (referred to as a “fraction”) or as many as 35 treatments over 7 weeks. Each radiation treatment usually takes 20 minutes or less, or can range from five to 60 minutes.

A common side effect of radiation therapy is fatigue. The exact cause of this side effect is unknown. Other less common side effects are nausea, vomiting, diarrhea and temporary liver pain. The radiation will damage the liver surrounding the tumor. This may lead to a change in how the liver functions, and the physician will do all they can to reduce the risk of injury to the liver. If the stomach needs to be treated, there may be an increased risk of developing an ulcer or bleed.

Several special types of radiation therapy can be used to reduce the volume of normal tissues that need to be irradiated. These are:

Three Dimensional Conformal Radiation Therapy (3D-CRT) uses computers to produce an accurate image of your tumor and surrounding organs. This allows multiple radiation beams to be shaped to the size and shape of your tumor.

Intensity Modulated Radiation Therapy (IMRT) better shapes high doses around your tumor. With IMRT, the intensity of each beam varies to deliver the highest possible dose to the tumor, and lower doses to nearby normal tissue.

Stereotactic Body Radiotherapy (SBRT) refers to the precise focused delivery of very potent radiation doses, delivered in fewer treatments (usually 5 or fewer treatments), requiring many more beams than conventional radiation therapy.

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External Beam Radiation Therapy