external beam radiation is often referred to as IMRT (intensity modulated radiation therapy). The radiation is produced by a large machine outside the body. Men go to a hospital or clinic for the treatment. On average, treatments are given 5 days per week for 8 1/2 weeks, requiring ongoing trips to the clinic.

Rectal side effects such as frequent bowel movements and rectal pain can occur with external radiation. As with other forms of prostate cancer treatment, urinary and sexual side effects are common and vary depending on the health of the patient, skill of the treating physician, dose of radiation received and the cancer itself.