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News of the Day ... In Perspective

7/3/2005

NAS stands by “no-threshold” theory for radiation damage

After 5 years of study, a panel of the National Academy of Sciences announced its support of the linear no-threshold (LNT) hypothesis for the carcinogenic effect of ionizing radiation. According to this hypothesis, even very low doses of radiation pose a risk of cancer (AP 6/30/05).

Exposure to an extra 100 mSv over a lifetime would produce a 1 percent excess risk of cancer, the panel concluded. This means that 43 out of 100 persons would get cancer, instead of the 42 who are expected to get cancer without the added radiation exposure.

The LNT hypothesis also raises fears about the use of medical diagnostics. Exposure from a chest x-ray is about 0.1 millisievert and from a whole-body CT scan, about 10 mSv, the panel stated. Helical CT scans can deliver a dose up to 18 mSv, and a virtual colonoscopy up to 78 mSv, compared to an average annual background dose of 2.4 mSv (240 mrem)/yr. (www.newportbodyscan.com/radiationdosage.htm).

Stringent regulations based on acceptance of the LNT hypothesis greatly increase the cost of nuclear-generated electricity and other beneficial applications of nuclear chemistry and physics.

In the event of the detonation of a terrorist nuclear weapon, trillions of dollars in clean-up costs would be needed to meet current standards based on the LNT hypothesis (Sydney J. Freedberg, Jr., National Journal, 6/25/05 ).

The NAS panel rejected evidence that low doses of radiation (up to 10,000 mGy per year) are generally harmless or even beneficial (J Am Phys Surg 2004;9:35), as well as developments in radiobiology pertaining to adaptive protective mechanisms (www.belleonline.com/BELLE_02_03web.pdf).

The Institute of Medicine of the NAS does not apply similar reasoning to the potential threat of neurologic damage from thimerosal in childhood vaccines (News of the Day 6/30/05).

Additional information:

Chen WL, et al. “Is Chronic Radiation an Effective Prophylaxis Against Cancer?” J Am Phys Surg, Spring 2004. (Cancer rates were reduced by more than 95 percent in persons accidentally exposed to doses around 50 mSv per year.)

Cuttler JM, Pollycove M. “Can Cancer Be Treated with Low Doses of Radiation?” J Am Phys Surg, Winter 2003.

Kauffman JM. “Diagnostic Radiation: Are the Risks Exaggerated?” J Am Phys Surg, Summer 2003.

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