External beam therapy is a type of therapeutic radiology that is delivered externally from a machine directed to the cancer inside the patient. Examples of external beam therapy machines include linear accelerators, cobalt machines, or orthovoltage X-ray machines. The type of machine used will be determined by the radiation oncologist. External beam therapy is the type of therapeutic radiology that is used most often.
External beam therapy delivers ionizing radiation to the cancer, destroying cancer cells.
To give healthy cells time to recuperate, patients undergoing external beam therapy receive small doses (fractions) of radiation at one time. Receiving small doses of radiation on a daily basis instead of a smaller number of larger doses helps to protect the healthy body tissue surrounding the diseased area.
Most patients receive radiation treatments on an outpatient basis. A typical schedule for external beam therapy treatment is to receive therapy once a day for 5 days a week over 2 to 9 weeks. In some cases where the treatment is palliative (to relieve symptoms rather than cure), the length of treatment may last only 2 to 3 weeks. The treatment process usually takes 10 to 30 minutes a day with much of the time spent positioning the patient. Treatment duration depends on the method of treatment delivery and the prescribed dose.
As the treatment progresses, the radiation oncologist will monitor the patient's progress and response to the treatment. Depending on the response to treatment, changes may be made to the radiation dose, the number of treatments, or the length of treatment.
Research is being done to study the effects of hyperfractionated external beam therapy, in which smaller doses of radiation are given more than once a day rather than just once a day. The results have been promising for certain types of tumors and cancers.
Although each facility may have specific protocols in place, generally, external beam therapy follows this process:
Generally, the patient will receive external beam therapy 4 or 5 times a week over a period of several weeks.
Depending on the location of the cancer, the patient may need to remove clothing. If so, he or she will be given a gown to wear.
The patient will be carefully positioned so that the area under treatment will receive the right amount of radiation. Special molds and other equipment may be used to ensure proper body position.
Shields may be used to protect normal body tissues from the radiation.
Once the positioning and shielding have been completed, the treatment will begin. The patient will need to remain very still during the treatment so that the radiation beam will reach the cancer with the proper dose.
When external beam therapy begins, the technologist will closely monitor the patient on a television screen in another room.
The treatment will be painless, and will last for only a few minutes.