Institute for Prostate and Urologic Cancers

Radiation Therapy for Prostate Cancer

Radiation therapy uses high-energy beams to kill cancer cells and minimize damage to healthy tissues. It is separated into two categories: external beam and brachytherapy.

External Beam Radiation

External beam radiation is energy used to irradiate the prostate from outside the body. Patients typically receive 39-43 external beam radiation treatments in about seven weeks. Each session lasts about 15 to 20 minutes. To help keep your body still during the therapy, you will be custom fitted for a cast called a Vac-loc--a special bag that contains styrofoam beads to form an exact shape of your leg--which will be put under your legs during each session. This cast will be made for you prior to receiving radiation. You will also have special marks placed on your body to make sure the radiation beams are positioned correctly during each treatment.

To locate the position of your prostate accurately, three gold seeds will be implanted into your prostate before you begin radiation treatments. The gold seeds are about the size of a pencil head. The seeds show up well on images of the prostate. The gold seeds are used as markers for daily verification of prostate position at time of treatment. The procedure to implant the seeds is very similar to a biopsy, and patients are awake during the procedure. An ultrasound probe is placed in the rectum, and the seeds are placed in the prostate through the rectal wall.

External beam radiation is done one of three ways:

  • Conventional therapy: applying radiation to an area over a large portion of the pelvis, which irradiates both cancerous and healthy tissue.
  • Three-dimensional conformal therapy: forming a three-dimensional picture of the individual lumps and swells of the prostate so radiation can be confined to the prostate and any relevant lymph nodes. This focused radiation therapy reduces the amount of radiation to healthy tissue which, in turn, reduces side effects. It also makes it possible to give a higher dose of radiation.
  • Intensity-modulated radiation therapy (IMRT)/TomoTherapy™: the most advanced of the three types, IMRT is able to focus not only on the prostate, but provide a higher dose of radiation to the tumors inside the gland, giving the cancer even more radiation than the prostate itself. The prostate, bladder and surrounding tissues sometimes move slightly within the body between treatments. IMRT is delivered through the TomoTherapy system, which changes the size, shape and intensity of the radiation beam to conform to the specific dimensions and position of a patient's tumor. The advantage to this type of focused radiation therapy lies in the ability of the machine to exactly locate the prostate prior to each treatment., limiting side effects and targeting cancer cells.


Brachytherapy ("brake-ee-therapy," also known as seed therapy) implants are radioactive seeds about the size of a poppy seed placed directly into the prostate. "Brachy" means "short," because the therapy is a short distance from the cancer, as opposed to external beam delivered from outside the body. The procedure has a short recovery time, is considered minimally invasive and limits the amount of radiation to surrounding tissues. Brachytherapy is a one-time procedure that more accurately delivers radiation and can be done either with lower-dose seeds left inside the body or, less commonly, with higher-dose seeds that are inserted and removed after a few hours.


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