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
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
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.