Fukushima Radiation Levels or Whole Body CT Scan - Which is Higher?


Radiation levels at the Fukushima Daiichi nuclear plant have been reported to significantly increase on Tuesday during a fire near reactor No. 4. Fortunately, these levels dropped rapidly after the fire was extinguished. The measured unit, in millisieverts, is difficult to put into perspective in our daily lives. How do these levels compare to a whole body CT scan?

In an article in The New York Times {graphic above} today, these levels are put into perspective.

As you can see, there is only one data point significantly above 10 millisieverts (per hour), the amount equivalent to a whole body CT scan. Let us hope that such management of radiation levels continues.


The New York Times has revised their graphic, clarifying that the "typical radiation doses are cumulative, not per hour." {For example, doses from a whole body CT scan.} This revision was made after I submitted the following letter on March 16 to their Editor {they may have heard from many readers on this point}:

The Times coverage of health risks associated with the Fukushima nuclear power plant has helped clarify numerous conflicting reports in the media. The graphic, however, could be misleading, since different units are used: radiation levels at the plant are a rate (millisieverts, mSv, per hour) and typical radiation doses are shown as a single point in time (e.g., whole body CT scan). When corrected as a rate per hour, whole body CT scans are greater (about 720 mSv) than even the highest level measured at the plant (400 mSv.) We must compare apples to apples!

Note that my estimated value of 720 mSv per hour for a whole body CT scan was calculated after conferring with a radiologist, who informed me:

The six milisievert CT scan takes about 15-30 seconds. If you leave the scanner on constantly for 5-10 minutes skin erythema and epilation can be seen as it was in the Cedars Sinai/ University of Alabama CT perfusion scans that got so much press last year.

Reporter Denise Grady of The New York Times shared some useful information in this article:

Another device, a sodium iodide detector, can be held an inch or so from the neck to check for radioactive iodine in the thyroid gland; if it detects any, the person may be given iodide pills.

In photographs from Japan, health workers appear to be screening members of the public with both Geiger counters and sodium iodide detectors.

If there is a suspicion that someone has been exposed to a large dose of radiation, the first test that doctors are likely to perform is a complete blood count, Dr. Vetter said. Abnormalities in the count -- fewer white cells than would be expected, for example -- can show up within a day or so, and give a ballpark estimate of how bad the exposure was.

"In Japan, it's very unlikely that a member of the public would get a dose of radiation that would result in a decrease in any blood cells," Dr. Vetter said. "If anyone got that kind of dose, it's likely people who are working in the nuclear plants themselves."

People with significantly lowered blood counts from radiation can be given drugs to stimulate their bone marrow to make more blood cells. Those drugs were not available in 1986, when a nuclear power plant in Chernobyl, Ukraine, blew up. Other drugs can be used to help rid the body of certain radioactive isotopes. But if the exposure was so high that the drugs do not help, people may need to be treated in the hospital -- put into isolation and given antibiotics to protect them from infection, and possibly blood transfusions as well. A bone marrow transplant may be a last resort, but, Dr. Vetter said, "the patient is in real trouble at that point."

Crops can be contaminated by fallout, which can cling to surface of plants at first and later be taken up by their roots.

Radioactive iodine has a half-life of only eight days -- the time it takes for half of it to decay or disappear -- so most of it is gone within about two months. But radioactive forms of the particulate cesium persist much longer, and in the regions affected by Chernobyl, they are still the main threats to human health and will be for decades.

Wild mushrooms, berries and animals have been found to be contaminated with cesium in areas contaminated by Chernobyl, and that is expected to last for decades. Lakes and freshwater fish may also be contaminated, but experts say ocean fish are less of a worry because the contaminants are more dispersed and diluted in the ocean than in lakes.

More like this

Continued from here ... Ana's feed starting Friday 8 PM TEPCO has raised the occupational limit of radiation for its workers to 150mSv/hr. Some workers have already been exposed in excess the old limit of 100mSv/hr. Workers who have been exposed to the limit will not be sent back in. -NHK morning…
Despite the deafening silence from TEPCO regarding questions over a physical breech in Reactor 2, it is now generally being considered that there is a breech in reactor 2. It is not clear if it is a hole in the containment vessel of some kind or just some disconnected or cracked pipes. Experts…
Much of the current news is about exposure and fallout. As a point of information, the Sievert is a unit of "dose equivliant" from exposure to ionizing radiation. It was designed to indicate relative levels of biological effects on living organisms. This measurement technique attempts to take…
The reactors at Fukushima continue to be hotter than "cold shutdown" levels, and at least one reactor (#1) is probably leaking from the core containment vessel. Fission products in high amounts, high pressure, and high temperature indicate that something close to fission is still happening…

It is fortuitous that the reactor is on the coast and most of the fallout is blowing out to sea. Water is a great neutron absorber.

I have heard this comment before however the obvious followup question is then how safe are CT scans?

By superdave (not verified) on 16 Mar 2011 #permalink

Good question.

According to the FDA: {http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProducts…}

Full-Body CT Scans - What You Need to Know

Using a technology that "takes a look" at people's insides and promises early warnings of cancer, cardiac disease, and other abnormalities, clinics and medical imaging facilities nationwide are touting a new service for health-conscious people: "Whole-body CT screening." This typically involves scanning the body from the chin to below the hips with a form of X-ray imaging that produces cross-sectional images.

The technology used is called "X-ray computed tomography" (CT), sometimes referred to as "computerized axial tomography" (CAT). A number of different types of X-ray CT systems are being promoted for various types of screening. For example, "multi-slice" CT (MSCT) and "electron beam" CT (EBCT) - also called "electron beam tomography" (EBT) - are X-ray CT systems that produce images rapidly and are often promoted for screening the buildup of calcium in arteries of the heart.

CT, MSCT and EBCT all use X-rays to produce images representing "slices" of the body - like the slices of a loaf of bread. Each image slice corresponds to a wafer-thin section which can be viewed to reveal body structures in great detail.

CT is recognized as an invaluable medical tool for the diagnosis of disease, trauma, or abnormality in patients with signs or symptoms of disease. It's also used for planning, guiding, and monitoring therapy. What's new is that CT is being marketed as a preventive or proactive health care measure to healthy individuals who have no symptoms of disease.

No Proven Benefits for Healthy People

Taking preventive action, finding unsuspected disease, uncovering problems while they are treatable, these all sound great, almost too good to be true! In fact, at this time the Food and Drug Administration (FDA) knows of no scientific evidence demonstrating that whole-body scanning of individuals without symptoms provides more benefit than harm to people being screened. The FDA is responsible for assuring the safety and effectiveness of such medical devices, and it prohibits manufacturers of CT systems to promote their use for whole-body screening of asymptomatic people. The FDA, however, does not regulate practitioners and they may choose to use a device for any use they deem appropriate.

Compared to most other diagnostic X-ray procedures, CT scans result in relatively high radiation exposure. The risks associated with such exposure are greatly outweighed by the benefits of diagnostic and therapeutic CT. However, for whole-body CT screening of asymptomatic people, the benefits are questionable:

â¢Can it effectively differentiate between healthy people and those who have a hidden disease?
â¢Do suspicious findings lead to additional invasive testing or treatments that produce additional risk with little benefit?
â¢Does a "normal" finding guarantee good health?
Many people don't realize that getting a whole body CT screening exam won't necessarily give them the "peace of mind" they are hoping for, or the information that would allow them to prevent a health problem. An abnormal finding, for example, may not be a serious one, and a normal finding may be inaccurate. CT scans, like other medical procedures, will miss some conditions, and "false" leads can prompt further, unnecessary testing.
Points to consider if you are thinking of having a whole-body screening:
â¢Whole-body CT screening has not been demonstrated to meet generally accepted criteria for an effective screening procedure.
â¢Medical professional societies have not endorsed whole-body CT scanning for individuals without symptoms.
â¢CT screening of high-risk individuals for specific diseases such as lung cancer or colon cancer is currently being studied.
â¢The radiation from a CT scan may be associated with a very small increase in the possibility of developing cancer later in a person's life.
â¢The FDA provides additional information regarding whole-body CT screening on its Computed Tomography (CT) Web site1.
FDA's Recommendation:

Before having a CT screening procedure, carefully investigate and consider the potential risks and benefits and discuss them with your physician.

Radiation levels drop at the inverse square from the source. The scans you are comparing this to are done up close, the levels measured here (at the plant's perimeter) are hundreds of meters from the source.

The point being that people chomping iodine pills in California are overracting, people in Tokyo are not in danger from these spikes, etc. But this does not tell us anything about people in the plant (if there are any) or about radiation of infrastructure.

Also, there is some conflation going on in the overall discussion between radiation and radioactive stuff. These are measured spikes of radioenergy. That is not the same thing as radioactive isotopes exiting a containment facility and getting in the air ... They are not unconnected sorts of things, but any reasonable discussion of these issues would include the different. If a spike (as in your graphic) is like the light coming out of a fridge when you open the door, that's one sort of situation. If it is energy coming from a plume of radioactive material entering the air column, it has a very different meaning.

In the end, we'll have to wait ... for the end. I'm not real sanguine on determining the significance of a major important event that is still very much underway. But, I suppose we are drawn to talk about these things. Human nature

The radiation coming from the power plant is a *rate*, i.e., is measured in msieverts PER HOUR. How can that rate measurement be compared to a DOSE measurement of the amount of radiation received during a CT scan or during an X-Ray. This is like saying my car goes 90 mph by you car goes 120 miles, so your car is faster, even though you didn't tell me how long it too your car to travel the 120 miles.

In the graphic are the numbers for, e.g., the chest x-ray the radiation rates that are used by the CT scanner while the person is being scanned (typically a second or so) or is it the total dose or radiation measured in msieverts that is received during the scan?

Thank you, Greg, for your insightful and thoughtful comment. I appreciate it.

Do you actually believe TEPCO's radiation readings, or the government's radiaton readings? Think for a moment about what we know: plants with spent fuel rods exposed after hydrogen explosions, fires nearby, cracks in at least one containment vessel and damage to other containment vessels, cooling pools for the active fuel rods going dry, cooling pools for the spent fuel rods going dry, and MOX fuel being used in at least one reactor! I don't trust the honest reporting of this situation, or the levels from TEPCO or the Japanese government. We need facts!

By Karen Wickman (not verified) on 16 Mar 2011 #permalink

Good point! My take on the NYT graphic is that the whole body scan value is just that - a value, and not a rate. Therefore, if I am correct, the hourly rate would many times greater, for a proper "apples to apples" comparison to the radiation rates released from the power plants. Please correct me, readers, if this interpretation is off base, as it is not my graphic.

Anther thing to note is that background radiation levels don't really tell you much about health risk. If I zap myself with X mSv from gamma rays that's a whole different animal than a microgram of plutonium that I inhaled.

You could conceivably have low measured radiation (in Sv) that could be called less than some background sources. But if you get the strontium in your body radiating away for several years, you get cancer.

Alpha particles aren't going to do much -- unless they get inside you (your skin blocks them reasonably well). Gamma rays will kill in short order (with a high enough exposure) but they can be stopped by getting further away (inverse square law) or putting a crapload of something solid between yourself and the source. Neutrons can be blocked, but you need certain materials and the damage they do to a given organ is different. And on and on... and it all falls under the catch-all of "radiation"

And dose rates matter. A few millisieverts isn't a big deal. Getting them all day every day is a bigger problem.

Mark B is correct. If you want to compare, you need to compare to "CT scans per hour".

By Andrew Foland (not verified) on 16 Mar 2011 #permalink

So, I looked up "Sodium Iodide Detector" and learned it is a scintillator which measures flashes of light on a crystal of sodium iodide, as it is exposed to radiation. Is this device actually unusually sensitive to radioactive iodide in the thyroid gland, as opposed to any other source of radiation?

By Whomever1 (not verified) on 16 Mar 2011 #permalink

I'm glad you put up the FDA advice on CT scans - I suspect most people don't think about the downsides when they get one.

This reminds me of the This American Life episode "Less is More," which delves into the issue of why healthcare costs are rising so quickly. In the segment about CT scans, a doctor explains that it's easier for him to just order a scan than to explain to the patient why a scan isn't necessary, deal with the likely pushback, and face the threat of a lawsuit if an unlikely bad outcome occurs. (The doctor explained this in the context of recommending a particular patient *not* get a scan, but I'm guessing that many doctors facing the same situation would order the scan for the reasons this doctor listed.)

While it's true that dosage drops with the square of the distance from the source, that's only relevant when the source is static. With a radioactive plume, the source is moving, such that when the plume arrives here, we in the US can no longer assume we're safely 8,000 km from the source.

The URL (only in Japanese) posted is the radiation level measured about 100 km south of the Fukushima plant in the past 24 hours. There are four measuring posts on the campus of Tokai Nuclear Power Plant in Ibaraki Prefecture. It is updated every 10 minutes. You will notice that they are measuring in nSy/hr (rate). Of course, the radiation level depends on wind direction and speed, but this gives you an indication as to how the radiation levels in the area and beyond. When Reactor #4 had fire, I was able to see the graph spiked little over 2000 nSy/hr (or 2 micro-Sy/hr). According to the graph that Jeff posted from NYT, the peak height 8 to 9 mSy/hr. This should give us some perspective on the subject.

Monitoring Post at Tokai Nuclear Power Plant

Dr. Toney, thanks for this post. This is the only scientifically oriented blog I could find on the subject.
Your letter to NYT highlights the distinction between the rate of radiation and the total amount of radiation. Unless the rate is too high, it is the amount that matters for human health. Dental x-ray, for example, is quite safe if used in the ordinary way, but it is not safe if you sit under an active machine for a whole week. Regrettably for the people near the plant, the situation is closer to the âsitting under an x-ray machine for a weekâ case.
The article also fails to investigate beyond the obvious, and consequently misses something that impacts more people.
Radiation hazard comes from two types of sources: (1) alpha, beta, gamma rays, and (2) radioactive atoms. Radioactive atoms are sources of alpha, beta and gamma rays, so if you have such an atom on you, you got yourself a personal, always-on, portable source of radiation that keeps on âgivingâ for a long time. The questions that one should ask about radioactive atoms are their half-lives, whether such atoms have a way to leave the body and so on. Unfortunately, such questions are not even asked, much less answered.
The âsmallâ amounts of radiation reported in airline passengers and (apparently) in California are almost certainly due to radioactive atoms and not alpha, beta and gamma rays. Even gamma rays, the most penetrative of the three, have line of sight limitations. Radioactive atoms on the other hand take time to travel, but can travel around the globe. Volcano dust has been known to travel around the globe; depending on the fineness of these particles, so can the radioactive material from Fukushima. Radioactive atoms spread by wind/people/water/food therefore represent a longer term, longer range concern.

You say that when corrected as a rate per hour, whole body CT scans are greater (about 720 mSv) than even the highest level measured at the plant (400 mSv). A typical Chest CT scan takes about 30-40 minutes to complete. Are you saying that the total amount of radiation induced into the body is close to at least 300 mSv?

Should we get our children out of Tokio?

By Jocelyn Hatch (not verified) on 22 Jun 2011 #permalink