Diagnostic X-rays use a very small dose of ionizing radiation to produce pictures of the inside of the body. Diagnostic X-ray exams account for about 90% of the radiation dose the population receives from medical sources. Chest X-rays (about 100 µSv) are the most common, and they account for about 25% of all X-ray exams, followed by X-rays of the shoulder, pelvis, and limbs (another 25%) and dental X-rays (10%). Note that no direct evidence of radiation ever causing any harm at the exposure levels encountered with diagnostic radiological examinations.
X-rays belong to so-called low-LET radiation. Biological effects of any radiation increase with the linear energy transfer (LET) were discovered. In short, the biological damage from high-LET radiation (alpha particles, protons, or neutrons) is much greater than that from low-LET radiation (gamma rays, X-rays). This is because the living tissue can more easily repair damage from radiation spread over a large area than that concentrated in a small area. Of course, at very high levels of exposure, X-rays can still cause a great deal of damage to tissues.
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.