Radiation: You May be Surprised I
The patient was a pale, unkempt, drug abuser, a jaundiced 24 year old woman, 6 months pregnant, with liver failure. She was surprisingly alert, but quite suspicious. As the technician and I approached her bed with the portable ultrasound unit, and following a brief explanation, she protested, "Just a minute, doc, you ain't givin' me no radiation, are you?"
Another memorable patient
We live in an age increasingly dominated by phobias, obsessed with the three C's, Cancer, Cholesterol, and Crime and newer risks threatening life if not liberty and our very survival. Such fears dominate us to a degree unknown in less sophisticated times. We have, of course, always lived in a dangerous world. Now, we have other perils to cope with, dangers such as terrorism, AIDS, flu epidemics, obesity and, Oh yes! Global Warming. Still, radiation phobia continues to be high on the popularity list. Perhaps the Internet, even more than the media, is partly to blame by driving the cultural ascendency of belief over fact. Ross Adey, a distinguished neurologist and researcher on electromagnetic fields has stated, "We dwell in a self-indulgent society without historical parallel. Our anxiety is reflected in an endless pursuit of physical perfection; our insecurities boggle the minds of our colleagues from Third World Countries."
Radiation* has always been part of our natural environment. When our present species evolved about 300,000 years ago, radiation levels were much higher than they are today. We are continually exposed to radiation from outer space in the form of cosmic rays, radioactive elements in the earth itself, from naturally occurring radon in the air, and from inside our own bodies from radioactive potassium-40 (K-40) we ingest from the environment. Don't get clutched, K-40 is only a tiny percentage of natural potassium, but it has a half life of 250 billion years, and it's not only found in bananas, but just about everything else we eat, so it won't disappear before we or the universe ends. Here's a thought: if you're sleeping regularly with someone, you'll get additional radiation from their K-40. Come to think of it, if you spend a lot of time traveling or love crowds, you'll get more K-40 from your surroundings than you would being a hermit
Radiation Measurements and Background Radiation
To measure the absorbed dose of radiation we are urged by the Government to use the newer SI unit, the sievert which has been replacing the old unit, the rem. The sievert ("Sv") or 1000 millisieverts, (mSv), equals 100 rems, which is quite a high dose, since 50 rems can cause acute and chronic changes in the bone marrow and GI tract. To change rems to sieverts, divide by 100. This can cause confusion, because the rem and millirem, mrem or 1/1000 of a rem are still used frequently.
Think of 1 mrem equivalent to .01 mSv, an easier way to look at it when we consider the wide range of units we're discussing while focusing particularly on the lower values. Let's see how many mrem or .01 mSv we're actually receiving from natural background radiation.
|Area||Average Background level in mSv/year||mrem/year|
|Atlantic and Gulf Coasts||0.7||70|
|France–Granite rock areas||5||500|
|India–Kerala Madras states||10-70||7 rem|
|Egypt (Northern Nile delta)||10||1000|
|Ramsar Iran (highest in the world)||260||2.6 rem|
Populations living > 10,000 feet receive over 4 times the world average whole body radiation from cosmic rays compared to that received by people living at sea level. Pilots and passengers of jet aircraft experience temporary exposure to high levels of cosmic rays, although nothing like the high doses received by astronauts. Such populations whether experiencing terrestrial or atmospheric exposures have not been shown to have increased cancer or other disease incidence. In Kerala, India in coastal areas near thorium sands the population receives up to seventy times the world average. Yet their cancer registry statistics fails to show any increased incidence of the disease in a population of 100,000, compared to 400,000 living in inland areas.
Past studies compared cancer rates and infant mortality in three regions of the U.S. with different background levels varying from 1.2 to 2 mSv or 120-200mrem per year failed to show any correlation with dose and adverse health effects. Similar studies performed in large populations in China and Brazil found no differences in disease and cancer rates.
Ramsar in Iran (Talesh-Mahalleh area), which probably has the highest background level of radiation in the world with a peak yearly dose of 260 mSv or 2.6 rem (compared with 0.0006 mSv or 0.06 mrem from a chest X-ray) has an effective dose equivalent several times in excess of the ICRP (International Committee on Radiation Protection)-recommended dose limits for radiation workers and up to 200 times greater than normal background levels. In Ramsar there are many hot springs in the area with high concentrations of radioisotopes, used as spas by locals and tourists. The article continues, "This high level of radiation does not seem to have caused ill effects on the residents of the area and even possibly has made them slightly more radioresistant, which is puzzling and has been called 'radiation paradox' ... It has also been reported that residents of the Ramsar area have healthier and longer lives. On the basis of this and other evidence including the fact that life had originated in a much more irradiated environment, some scientists have questioned the validity of the linear no threshold model, (vide infra) on which all radiation regulations currently depend. Others point out that some level of radiation might actually be good for health and have a positive effect on population based on the controversial radiation hormesis model, by jump starting DNA repair mechanisms inside the cell."
Radiation from Medical Imaging Procedures
A principal source of confusion about radiation exposure and absorbed doses has been the breath taking failure of many writer to distinguish between dangerous, high, medium, and low or inconsequential (since it cannot be eliminated) background radiation as discussed above.
For one summary of radiation doses received from conventional X-ray, CT, PET and nuclear medicine procedures, see here. (The author, by the way, mistakenly replaces.01mSv with mSv.) For simplicity, I am switching here to mrem only. The range of (acute) doses is generally comparable to average background radiation per year cited above.
|X-ray||1-90 mrem for X-ray up to 700 mrem for barium studies|
|CT||200-1140 mrem (coronary arteriography 450-5700 mrem)|
|Nuclear||170-1200 mrem, average|
|PET||700 mrem range|
Recall, however, for X-ray and CT we're measuring radiation only to the target organ; while nuclear and PET, radiation exposure is to the whole body.
Ranges and Effects of Differing Radiation Exposure in Rem
Recall, these doses in rem, unlike those above, are in thousands of millirem. For sieverts, divide by 100.**
|5-20||Possible late effects; possible chromosomal damage.|
|20-100||Temporary reduction in white blood cells.|
|100-200||Mild radiation sickness within a few hours: vomiting, diarrhea, fatigue; reduction in resistance to infection.|
|200-300||Serious radiation sickness effects as in 100-200 rem and hemorrhage; exposure is a Lethal Dose to 10-35% of the population after 30 days (LD 10-35/30).|
|300-400||Serious radiation sickness; also marrow and intestine destruction; LD 50-70/30.|
|400-1000||Acute illness, early death; LD 60-95/30.|
|1000-5000||Acute illness, early death in days; LD 100/10.|
Japanese Survivors of the Atomic Bomb
In large groups of studies of Japanese survivors among the populations in excess of 100,000 with an average of almost 200-rem radiation dose to the whole body, showed an increase in leukemia incidence for those receiving 50 rems (50,000 millirem) or more with an increased incidence beginning 2 years after exposure, peaking at 10 years, but with a value of only 5% above controls, returning to control levels by 20 years. The interesting fact is that "for the population receiving lower doses, in the range of 0-9 rem, no significant correlation between radiation exposure and carcinogenesis has been found to date." *** For more detailed and current data, see here.
The reader can be forgiven for skipping much of the detailed dose summaries given above. My attempt was to consolidate a lot of data concerning radiation exposure, and to compare the dose estimates in three categories 1. Amount of background radiation received from natural sources by populations living in several geographic regions,
2. Radiation doses, received from medical imaging, and finally, 3. Ranges and effects of relatively huge radiation exposure using the example of Japanese survivors of the atomic bomb 35 years after the attacks in August, 1945. Allowing for differences in effect of radiation due to duration of exposure, e.g. acute doses received have more potential for damages than doses like background received over a month, year, or lifetime, we can conclude the following:
Radiation doses received by Japanese survivors of the atomic bomb causing leukemia, cancer, or life-shortening -1% of those exposed-receive tens of thousands to hundreds of thousands times more radiation than do all of us from natural background radiation and that due to medical exposure.
Stay tuned for the next newsletter to follow soon.
*Radiation, propagated energy, occurs as the electromagnetic (EM) spectrum, a portion of which is seen in charts displayed in these excellent articles: here and here. This EM spectrum of energies, though they produce different effects, are fundamentally the same thing, ranging from low energy,(longer wavelength low frequency) radio waves, including television, mobile phones, wireless networking, microwaves used in heating, thence to infrared, and visible light, ultraviolet, with gradually increasing energies, -shorter wavelength, higher frequency- extending to X-rays, gamma rays from radioactivity, cosmic rays, and even higher energies.
The Standard Model of particle physics is a theory of three of the four known fundamental interactions: electromagnetism, the strong and the weak nuclear force, and the mysterious, elusive fourth, gravity. Current theory holds these forces were created at the origin of the universe about 14 billion years ago in what is generally accepted as "The Big Bang."
**Source: Nuclear Arms Race: Craig and Jungerman, 1990
***Advisory Committee On the Biological Effects of Ionizing Radiation. The Effects On Populations of Exposure To Low Levels of Ionizing Radiation. Washington, DC: National Research Council, National Academy of Sciences, National Academy Press, 1980.
Martin F. Sturman, MD, FACP
Copyright 2010, Mathemedics, Inc.
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