External beam radiation therapy is the most common method of radiotherapy used for cancer patients. The radiation is created by a linear accelerator and can be directed to large areas of the body and to multiple areas if cancer has spread. Prostate cancer patients typically receive external beam radiation on an outpatient basis for five days a week over a period of eight weeks.
In the short-term, patients may experience frequent urination and bowel movements, but disabling fatigue is rare. The most common long-term side effects associated with external beam radiation therapy are impotence, rectal bleeding, and – very rarely – incontinence.
Intensity-Modulated Radiation Therapy
Intensity modulated radiation therapy (IMRT), a form of external beam radiation therapy, represents a major technical innovation in modern radiation therapy. IMRT is an advanced three-dimensional (3D) conformal treatment that uses non-uniform beam intensity patterns with computer-aided optimization to deliver higher doses of radiation therapy to the tumor and decrease the dose of radiation to normal tissues. This means that higher doses of radiation can be directed at the cancerous tissue with fewer risks of side effects.
Typically, radiation oncologists use five fields of radiation that overlap directly on the prostate, centering the highest dose on the organ. Radiation from the individual fields will reach the rectum and other surrounding organs, but at much lower doses.