By: Board Certified Nuclear Medicine Expert
It is common in the U.S. today to find patients who are concerned that diagnostic medical radiation may cause cancer, and some of these patients may be hesitant to undergo radiology procedures themselves or be wary of allowing their minor children to undergo such procedures. If they develop a cancer, they may try to blame it on medical radiation from previous radiology procedures. As 38% of women and 46% of men will develop cancer (not counting common localized skin cancers), and 23.5% of people will die of cancer, there is, unfortunately, plenty of cancer to go around.
While we have known for well over 100 years that high doses of radiation can cause cancer, the effects of low doses of radiation were less certain until relatively recently. To err on the side of safety, radiation regulators years ago adopted the Linear, Non-Threshold hypothesis, or LNT. It assumed that lower doses of radiation, all the way down to zero, were proportionally less carcinogenic than high doses but that no dose of radiation was “safe”. There has never been any scientifically valid support for this theory, but it is the entire basis of our radiation regulatory system today. Several thousand scientific papers now show that low doses of radiation either have no effect or are beneficial; the beneficial effect is known as “hormesis”. Hormesis is a common phenomenon with other entities. For example, your body needs low levels of iron for compounds such as hemoglobin, but high levels of iron can kill you. Your body needs low levels of vitamin A for normal vision, but high levels can kill you as well. Unfortunately, this new data has not resulted in changes to the regulatory framework regarding radiation.
Much of our information on radiation carcinogenesis has come from the Life Span Study of 85,572 survivors of the Hiroshima and Nagasaki atomic bombs in 1945. This study, which went from 1950 to 1997, has numerous problems. One of the most significant is the choice of a “control” group. One needs to know the baseline cancer rate to then determine the supposed increased cases of cancer from the radiation. Initially, two control groups were chosen. One was more than 3 km from where the bombs fell, and these people had no excess radiation dose from the bombs. Another control group was chosen from within the 3 km radius that was composed of people who received less than 0.5 rem from the bombs. (For comparison, a CT scan gives about 1 rem, natural background in the U.S. averages 0.3 rem/y, and radiation workers are allowed 5 rem/y from work activities). As time went on, scientists noted that the control group within the 3 km radius (who received up to 0.5 rem) had about 10% less cancer than the control group that received no radiation at all from the bombs. The scientists decided that the “true” control was the group that received the low dose of radiation and had the lower incidence of cancer. Those who received higher doses of radiation were compared with them. In the event that this control group was actually demonstrating hormesis, that extra 10% of cancer formed the basis of the “radiation-induced” cancers claimed in the study. In fact, the total number of cancers blamed on radiation in this large group of survivors over 52 years after the bombs is 340. If we used the other control group, this number would be much, much lower. Other problems with the Life Span Study include uncertainties in actual doses, an underestimate of the dangers of neutron radiation (and a consequent overestimate of the x-ray and gamma ray radiation, which is most of medical radiation), and certain statistical problems. In addition, the radiation received from the bombs is “acute” radiation. It was received all at once. If radiation doses are spread out over time, called “chronic” radiation, there is much more opportunity for relpair of radiation damage and stimulation of general repair mechanisms. Therefore, while LNT calculations use data from the Life Span Study to estimate cancer risk at low doses, the data of the Life Span Study itself is in substantial question for a number of reasons.
Changing Position of Diagnostic Radiation
In 2002 the FDA’s Center for Devices and Radiological Health went to war against screening CT scans. In 2004, a paper of questionable quality purporting to show carcinogenesis at low doses using the Life Span Study data and the LNT hypothesis hit the news media, and radiation hysteria really appears to have increased since then. It is interesting that the radiological physician’s professional societies did not stand up and claim fraud. They rather jumped on the FDA bandwagon in order to increase market share (suggesting that board-certified radiology experts would be better at lowering radiation doses than other physicians who used x-ray and fluoroscopy machines and CT scanners).
As is the case in many areas of research and medicine, there is quite a bit of misinformation based on conjecture, flawed studies and pursuit of other agendas. Given the pervasiveness, acceptance and broad dissemination of misinformation made possible by modern media and technology, lawsuits resulting from such misinformation are therefore not unreasonable and to be expected. Failure of such suits when challenged with more comprehensive research and supported by qualified medical experts should also come as no surprise.
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