Internal radiation therapy or brachytherapy is less common than external radiation therapy. Internal radiation therapy involves the placing of materials that emit radiation directly in the human body. Brachytherapy can be either temporal or permanent. In the temporal type the radioactive material is place in the human body for a certain amount of time and is afterwards removed. In the permanent type the radioactive material is placed in the human body and it is left their permanently; it is never removed again. As time passes the radiation from the material will diminish until it will no longer emit any type of radiation.

The radioactive material is inserted in the human body by means of a needle, applicator or catcher. The exact location may be determined by the use of ultrasounds, x-rays or CT-scans. The procedure may be performed under a general anesthetic and it may require a stay in hospital after the procedure is performed.

Precautions must be taken in order to protect the staff and visitors from radioactivity. The surrounding area where the radioactive material has been implanted will be radioactive but the whole body of the patient is not radioactive.  Brachytherapy has the advantage to treat a small area using a high dosage of radioactive material within a small span of time.