Even Low-Dose X-rays Increase Cancer Risk

Exposure to x-rays and gamma rays, even at low-dose levels, increases cancer risk, according to new findings of a wide-ranging five-year study by a U.S. National Research Council (NRC, Washington, DC, USA).

"There appears to be no threshold below which exposure can be viewed as harmless,” said Dr. Herbert L. Abrams, professor emeritus of radiology at Stanford University (CA, USA) and Harvard University (Boston, MA, USA) and a member in residence at the Center for International Security and Cooperation (CISAC, Stanford, CA, USA) in the Freeman Spogli Institute for International Studies. Dr. Abrams was one of two physicians and the only member from Stanford on the committee of 16 international experts in fields including genetics, epidemiology, radiation biology, cancer biology, radiology, and physics.

The landmark 700-page advisory report to the U.S. government, titled "Biological Effects of Ionizing Radiation (BEIR) VII,” was completed in July 2004, close to the eve of the 60-year anniversary of the Hiroshima and Nagasaki bombings. Beginning with the first BEIR study, published in 1956, the reports have used information from the Life Span Study by the Radiation Effects Research Foundation in Japan, which continues to follow developments among a cohort of 120,000 people who were in Hiroshima or Nagasaki at the time of the bombings, as well as other radiation-exposure studies.

The new report corroborates that even very low doses of radiation can produce cellular injury. The committee defined "low-dose” as a range from near zero up to approximately 100 milliSievert--about 10 times that from a computed tomography (CT) scan, 1,000 times greater than a mammogram, and 30-40 times the annual background exposure a person encounters.

The key findings of the report included that for boys, radiation exposure in the first year of life generates three to four times the lifetime cancer risk as exposure to the same dose between the ages of 20 and 50. Female infants have nearly twice the risk as male infants. For women, the risks of developing cancer after exposure to radiation were 37.5% higher than for men. The risks for all solid tumors, such as lung and breast tumors, when combined, were nearly 50% greater for women than for men.





Related Links:
U.S. National Research Council
Stanford University