Understanding X-rays (cont.)
Diagnostic X-rays Do Not Increase the Risk of Cancer
No studies of radiation in humans have demonstrated an increase in cancer at the doses used in diagnostic
- A-bomb survivors (from Hiroshima and Nagasaki) who had large doses-greater than the equivalent of 150 years of background radiation-had a slight increase in cancer. In the last 50 years there was an average of fewer than 10 radiation-induced cancer deaths per year in about 100,000 A-bomb survivors. A-bomb survivors who received a dose less than the equivalent of 60 years of background radiation showed no increase in the incidence of cancer. Survivors in that dose range tended to be healthier than the unexposed Japanese. That is, their death from all causes was lower than for the unexposed Japanese. The improved health of those with low doses more than compensated for the radiation-induced cancer deaths, so that A-bomb survivors as a group are living longer on the average than the unexposed Japanese controls.
- Nuclear shipyard workers were much healthier than non-nuclear shipyard workers. Evidence for health benefits from low-dose rate radiation comes from the nuclear shipyard workers study (NSWS) over a decade ago. This DOE-sponsored study found that 28,000 nuclear shipyard workers with the highest cumulative doses had significantly less cancer than 32,500 job-matched and age-matched controls. The low death rate from all causes for the nuclear workers was statistically very significant. Nuclear workers had a death rate 24% (16 standard deviations) lower than the unexposed control group.
- People living in areas with high natural background radiation generally have less cancer. Humans receive ionizing radiation from several natural sources: radioactivity inside their body, radioactivity outside their body, and cosmic rays. The amount of radiation from these last
two sources varies with the geographical location and the material used in the buildings where you work and live. In addition, the contribution from radon varies depending on the construction of
a person's home and the amount of uranium in the soil beneath it. If ionizing radiation is a significant cause of cancer, we would expect the millions of people who live in areas with high natural levels of radiation to have more cancer. However, that is not the case. The
seven western U.S. states with the highest background radiation-about twice the average for the country (excluding radon contributions)-have a 15% lower cancer death rate than the average for the country.
- Radon in mines increases lung cancer. (Radon is a radioactive gas found naturally in soil.) Uranium miners had a higher incidence of lung cancer from the high concentrations of radon in underground mines. This was the basis for the Environmental Protection Agency (EPA) to estimate that high levels of radon in homes cause thousands of lung cancer deaths each year in the
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