Permanent (low dose rate, or LDR) brachytherapy
In this approach, pellets (seeds) of radioactive material (such as iodine-125 or palladium-103) are placed inside thin needles, which are inserted through the skin in the area between the scrotum and anus and into the prostate. The pellets are left in place as the needles are removed and give off low doses of radiation for weeks or months. Radiation from the seeds travels a very short distance, so the seeds can give off a large amount of radiation in a very small area. This limits the amount of damage to nearby healthy tissues.
Usually, around 100 seeds are placed, but this depends on the size of the prostate. Because the seeds are so small, they cause little discomfort, and they are simply left in place after their radioactive material is used up.
You may also get external beam radiation along with brachytherapy, especially if there is a higher risk that your cancer has spread outside the prostate (for example, if you have a higher Gleason score).