Prostate Cancer: Radioactive Seed Implants
Radioactive seed implants are a form of radiation therapy for prostate cancer. Brachytherapy, or internal radiation therapy, are also terms used to describe this procedure. There are two types of prostate brachytherapy: permanent and temporary.
Compared to external radiation, which requires eight to nine weeks of daily treatments, convenience is a major advantage of brachytherapy.
Permanent (Low Dose Rate) Brachytherapy: LDR
A doctor or clinician implants radioactive (iodine-125 or palladium-103) seeds into the prostate gland using an ultrasound for guidance. The number of seeds and where they are placed is determined by a computer-generated treatment plan tailored for each patient. Anywhere from 40 to 100 seeds are commonly implanted.
The implants remain in place permanently, and become biologically inert (no longer useful) after a period of months. This technique allows a high dose of radiation to be delivered to the prostate with limited damage to surrounding tissues.
Temporary (High Dose Rate) Brachytherapy: HDR
With this technique, hollow needles are placed into the prostate gland and filled with radioactive material (iridium-192) for 5-15 minutes. After the treatment both the iridium and the needles are removed. This is repeated two to three times over the next several days.
Who Is Eligible For This Procedure?
Seed implants are relatively low-energy sources, and subsequently have limited tissue penetration. Therefore, the best candidates for these procedures are patients who have a cancer that is contained within the prostate and is not very aggressive. The usual criteria for treatment include a PSA level of less than 10, a Gleason score (which measures the aggressiveness of the tumor) less than or equal to six, and minimal or no abnormality on the digital rectal exam.
What Happens Before The Procedure?
A transrectal ultrasound is done to provide the radiation oncologist with specific details about your case. Newer techniques using a CAT scan or MRI may be used to guide the proper placement of the implants. This information is used to custom-design the treatment plan for you. Another option is for the ultrasound and treatment plan to be done at the same time as the radioactive seeds are implanted.