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Are X-Ray Procedures Equivalent, in Extra Radiation Dose,
To Taking an Airplane Trip?

By John W. Gofman, M.D., Ph.D, and Egan O'Connor, Editor of CNR Books
February 28, 2000

          X-ray-givers sometimes claim that the extra radiation received during an x-ray procedure will be no greater than the extra radiation received during an airplane trip. Often, they fail to mention that x-ray doses can vary by 10,000-fold, from one type of x-ray procedure to another. Only a few types of procedures deliver a dose equivalent to the extra dose from an airplane flight. Most x-ray procedures will deliver a dose much higher.

          Unless an x-ray-giver can tell you what your absorbed x-ray dose will be, he/she cannot properly assure you that it will be equivalent to the extra radiation dose from an airplane trip. Your dose may be 100 times or 10,000 times higher.

          The extra radiation dose from flying depends on altitude and on latitude. The extra dose on commercial flights in the USA is about 0.0003 unit (rem) per hour of flying. The entire body absorbs the extra dose. By contrast, medical x-ray procedures irradiate only part of your body --- say, one-third. Therefore, the airplane dose needs multiplication by 3 before it is compared with an x-ray procedure which irradiates one-third of the body. To round-off, we can "credit" each hour of flying as an extra medical exposure of 0.001 unit.

          Here is a reasonable approximation: If an x-ray procedure, covering one-third of your body, delivers an average dose of 1 unit (rem, rad, roentgen) to the internal organs in the x-ray beam, then the procedure delivers an extra radiation dose equivalent to about 1,000 hours of flying.

10.000 rem absorbed internal dose from x-rays ~ 10,000 hrs flying
1.000 rem absorbed internal dose from x-rays ~ 1,000 hrs flying
0.100 rem absorbed internal dose from x-rays ~ 100 hrs flying
0.010 rem absorbed internal dose from x-rays ~ 10 hrs flying

          Certain "nuclear medicine" procedures cause whole-body irradiation. For instance, the whole-body internal dose from the common thallium-201 injection is estimated by the thallium-suppliers at about 0.45 rad, for an adult. This would be approximately equivalent to 450 hours of flying times 3, or 1,350 hours of flying.