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Definition of Interstitial radiation therapy
Medically reviewed by Min Clinic Staff | Updated: January 2026
Interstitial radiation therapy: Radiation treatment given by placing radioactive material directly into the target, often a tumor.
For example, in treating prostate cancer, radioactive seeds are implanted in the prostate gland. The seeds might be titanium-encased pellets containing the radioisotope iodine-125.
Interstitial radiation therapy is also called seed implantation or brachytherapy (brachys being Greek for short).