Radiation therapy uses high-energy x-rays, either beamed from a machine or emitted by radioactive seeds implanted in the prostate, to kill cancer cells. When prostate cancer is localized, radiation therapy serves as an alternative to surgery. External beam radiation therapy is also commonly used to treat men with regional disease, whose cancers have spread too widely in the pelvis to be removed surgically, but who have no evidence of spreading to the lymph nodes. In men with advanced disease, radiation therapy can help to shrink tumors and relieve pain.
External beam radiation therapy generally involves treatments 5 days a week for 6 or 7 weeks. The treatments cause no pain, and each session lasts just a few minutes. In many cases, if the tumor is large, hormonal therapy may be started at the time of radiation therapy and continued for several years. The primary target is the prostate gland itself. In addition, the seminal vesicles may be irradiated (since they are a relatively common site of cancer spread). Radiating the lymph nodes in the pelvis, once common practice, has not proven to produce any long-term benefits for most patients, but it may be necessary in certain circumstances.
Radiation can also be delivered to the prostate from dozens of tiny radioactive seeds implanted directly into the prostate gland. This approach, known as interstitial implantation or brachytherapy, has the advantage of delivering a high dose of radiation to tissues in the immediate area, while minimizing damage to healthy tissues such as the rectum and bladder.
As practiced today, internal radiation therapy relies on ultrasound or CT to guide the placement of thin-walled needles through the skin of the perineum. Seeds made of radioactive palladium or iodine are delivered through the needles into the prostate, according to a customized pattern using sophisticated computer programs to conform to the shape and size of each man's prostate.