Interstitial Radiation or Seeds (Brachytherapy)

Brachytherapy, also referred to as seed implantation, is a type of internal radiation therapy used to treat prostate cancer. The radioactive material or source is placed directly inside the prostate. The exact dose of radiation is determined so that the cancer cells get enough radiation, but the surrounding normal tissue does not.  Brachytherapy may be used alone to treat low risk prostate cancer, or in combination with external radiation for intermediate or high risk prostate cancer.  Two types of brachytherapy are available: one is permanent and the other temporary.

Permanent or Low-dose brachytherapy
Permanent brachytherapy involves low-dose radioactive seeds resembling grains of rice and consisting of an outer titanium shell with radioactive material inside, which may be iodine-125, pallidium-103, or cesium-131. While the patient is under spinal or general anesthesia, the seeds are inserted into the prostate through the perineum, the area between the scrotum and the anus. The seeds remain in place permanently and give off low doses of radiation until they are no longer radioactive. Should there be a risk that the cancer has spread through the capsule of the prostate, external beam radiation may also be added.

Temporary or High-dose brachytherapy
Another method, sometimes used for the more aggressive or higher risk cancers, is temporary or high-dose rate brachytherapy. This type of brachytherapy uses high-dose pellets of iridium-192 that are contained inside small plastic catheters that are inserted through the perineum into the prostate. The pellets are withdrawn by computer controlled system so that they stay inside the prostate for only several minutes at positions where the cancer is located, and then are removed.. This is usually perfomed as an in-patient, where 2 or 3 applications are needed, separated by about six hours.  After the last treatment is completed, the catheters are removed. Often, external beam radiation is also added to cover the outer capsule of the prostate.

Possible Side Effects of Brachytherapy

• Frequent urination caused by irritation of the urethra
• Urinary urgency incontinence
• Diarrhea (rare)
• Rectal pain and burning (rare)
• Impotence

Advantage of brachytherapy

• One-stop outpatient treatment rather than weeks of daily visits
• Radiation is concentrated in the prostate gland, not in the healthy tissue
• Ultrasound permits precise seed placement
• Long-term prognosis is good
• Less rectal irritation than external beam radiation therapy

Disadvantages of brachytherapy

• Urgency sensation, when it occurs, may take up to a year to resolve
• PSA may rise 12-18 months after treatment (“PSA bounce”), so more delayed drop in PSA to lowest levels compared to surgery or cryotherapy
• Rectal irritation (rare)
• Treatment limited to small size prostate. Large prostates may require hormone therapy to shrink the gland before treatment
• Can make urinary symptoms much worse for up to a year, so need to have medical treatment of symptoms or have minimally invasive therapy of prostate enlargement before brachytherapy
• Prior shaving of prostate (TURP) may prevent adequate seed placement