Nuclear medicine is a medical science that involves the application of radioactive substances for diagnostic and treatment purposes. Nuclear medicine uses very small amounts of radioactive materials called radiotracers, which are taken internally, for example, intravenously or orally. Then, external detectors (gamma cameras) capture and form images from the radiation emitted by the radiotracers. Sometimes the radioactive drug can be used in the treatment itself: an example is the treatment of thyroid disease with I-131. Nuclear medicine imaging is unlike a diagnostic X-ray, where external radiation is passed through the body to form an image. It also provides unique information that often cannot be obtained using other imaging procedures.
The average effective dose for most nuclear medicine procedures varies between 0.3 and 20 mSv. The common bone scan with 600 MBq of technetium-99m has an effective dose of approximately 3.5 mSv. These doses can be compared with the average annual effective dose from the background radiation of about 3 mSv.
In the following points, we try to express enormous ranges of radiation exposure and a few doses from medical sources.
- 1 µSv – Eating one banana
- 1 µSv – Extremity (hand, foot, etc.) X-ray
- 5 µSv – Dental X-ray
- 10 µSv – Average daily dose received from natural background
- 40 µSv – A 5-hour airplane flight
- 100 µSv – Chest X-ray
- 600 µSv – mammogram
- 1 000 µSv – Dose limit for individual members of the public, total effective dose per annum
- 3 650 µSv – Average yearly dose received from natural background
- 5 800 µSv – Chest CT scan
- 10 000 µSv – Average yearly dose received from a natural background in Ramsar, Iran
- 20 000 µSv – single full-body CT scan
- 80 000 µSv – The annual local dose to localized spots at the bifurcations of segmental bronchi in the lungs caused by smoking cigarettes (1.5 packs/day).
- 175 000 µSv – Annual dose from natural radiation on a monazite beach near Guarapari, Brazil.
- 5 000 000 µSv – Dose that kills a human with a 50% risk within 30 days (LD50/30) if the dose is received over a very short duration.
As can be seen, low-level doses are common in everyday life.