External Beam
In external beam radiation therapy, the radiation beam comes from a machine that does not touch the patient's skin or the tumor. Special treatment machines create high-energy photons that target and kill the cancer cells while sparing the surrounding healthy tissue from damage. Receiving external beam radiation is similar to having an X-ray taken. Whereas cancer cells are killed by radiation beams, normal cells are able to repair whatever damage is caused by the radiation and recover.
Several different external beam radiation therapy techniques are used. Depending on the location, size and type of the tumor or tumors, a patient may receive one or a combination of these techniques. Using sophisticated treatment-planning software, the radiation oncology team plans the size and shape of the beam, and how it will be directed at the body, to effectively treat a tumor. To minimize side effects, these treatments are typically given every day for a number of weeks.
Three-Dimensional Conformal Radiation Therapy (3D-CRT)
Tumors usually have an irregular shape. 3D conformal radiation therapy (3D-CRT) uses sophisticated computers and computer assisted tomography scans (CT or CAT scans) and/or magnetic resonance imaging scans (MR or MRI scans) to create detailed, 3D representations of the tumor and the surrounding organs. The radiation oncologist can use these computer-generated images to shape radiation beams to the exact size and shape of the tumor. The tools used to shape the radiation beams are multileaf collimators or blocks. Because the radiation beams are very precisely directed, healthy tissue nearby receives less exposure to radiation. The radiation and physics work together to create mathematical models to ensure that normal organs do not receive excessive doses of radiation.
Specific types of external beam therapy are listed below, and the radiation oncologist will recommend the treatment he or she believes will be most effective for each particular type of cancer.