The difference between radiation therapy and radioactive iodine therapy.

I am finding that a great deal of people think I am going through radiation therapy for my thyroid cancer. That is not the case. I was administered a radioactive iodine pill to help kill any of the thyroid that may still exist in my body. Let me try to explain the difference. My therapy is referred to as systemic radiation therapy.

Radiation therapy uses high-energy radiation to shrink tumors and kill cancer cells. The radiation may be delivered by a machine outside the body (external-beam radiation therapy). External-beam radiation therapy is most often delivered in the form of photon beams (either x-rays or gamma rays). A photon is the basic unit of light and other forms of electromagnetic radiation. It can be thought of as a bundle of energy. The amount of energy in a photon can vary. For example, the photons in gamma rays have the highest energy, followed by the photons in x-rays. Patients usually receive external-beam radiation therapy in daily treatment sessions over the course of several weeks.

Radiation therapy may come from radioactive material placed in the body near cancer cells (internal radiation therapy, also called brachytherapy. Internal radiation therapy is radiation delivered from radiation sources (radioactive materials) placed inside or on the body. Several brachytherapy techniques are used in cancer treatment. Interstitial brachytherapy uses a radiation source placed within tumor tissue, such as within a prostate tumor. Intracavitary brachytherapy uses a source placed within a surgical cavity or a body cavity, such as the chest cavity, near a tumor. In brachytherapy, radioactive isotopes are sealed in tiny pellets or “seeds.” These seeds are placed in patients using delivery devices, such as needles, catheters, or some other type of carrier. As the isotopes decay naturally, they give off radiation that damages nearby cancer cells. If left in place, after a few weeks or months, the isotopes decay completely and no longer give off radiation. The seeds will not cause harm if they are left in the body. Brachytherapy may be able to deliver higher doses of radiation to some cancers than external-beam radiation therapy while causing less damage to normal tissue.

In systemic radiation therapy, a patient swallows or receives an injection of a radioactive substance, such as radioactive iodine or a radioactive substance bound to a monoclonal antibody. Radioactive iodine -131, is a type of systemic radiation therapy commonly used to help treat some types of thyroid cancer. Thyroid cells naturally take up radioactive iodine.