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Friday, July 12, 2013

Can CT Scans Give You Cancer?

Here's a doubt-mongering article which asks the question in Salon.

And contrary to the line under the headline, the benefits will outweigh the risks if the medical staff has made proper considerations.  In other words, what a gross generalization that line is.

Let's ask these questions:

Do CT scans emit ionizing radiation?  Answer:  Yes.

Does ionizing radiation damage DNA?  Answer: Yes.

Does increased DNA damage increase cancer risk?  Answer: Yes.

Therefore, does it follow that getting CT scans increase one's risk of getting cancer?  Answer: Yes.

Does that mean CT scans can give you cancer?  Answer: Yes, they can. But the risks are low compared to the benefits.

6 comments:

  1. Good article in The Lancet.

    "Findings

    During follow-up, 74 of 178 604 patients were diagnosed with leukaemia and 135 of 176 587 patients were diagnosed with brain tumours. We noted a positive association between radiation dose from CT scans and leukaemia (excess relative risk [ERR] per mGy 0·036, 95% CI 0·005—0·120; p=0·0097) and brain tumours (0·023, 0·010—0·049; p<0·0001). Compared with patients who received a dose of less than 5 mGy, the relative risk of leukaemia for patients who received a cumulative dose of at least 30 mGy (mean dose 51·13 mGy) was 3·18 (95% CI 1·46—6·94) and the relative risk of brain cancer for patients who received a cumulative dose of 50—74 mGy (mean dose 60·42 mGy) was 2·82 (1·33—6·03)."

    But... but... according to Wade Allison, 100 mSv should be safe. Per month!

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    1. Good study, thanks Martin.

      At least Allison admits he's not an expert.

      At 1:25 here:

      www.youtube.com/watch?v=UT-y-YBvvP4&list=PL48643C82BAFE15E3

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    2. ;-)

      By the way, I see a pattern here. According to this article, also the risk of thyroid cancer in young people is elevated already for moderate total doses.

      The commonality seems to be that 1) in young people, vulnerable tissues are still growing and cells dividing quickly, making them more vulnerable, but also 2) the incidence of cancer tends to increase with age, making the background for these specific cancers very low. The radiation-caused excess risk stands out like a sore thumb.

      There are echoes of Alice Stewart's early work here.

      BTW it seems according to this article, the discovery of the elevated thyroid tumor rates in young people soon after Chernobyl came as something of an unpleasant surprise. The article is also otherwise recommended reading. It correctly IMO diagnoses the destructive role of dishonesty in these issues.

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  2. The pattern really goes back to the 1906 work of Bergonie & Tribondeau (called the Law of B&T)who first described differences in radiosensitivity based on mitotic rate, long mitotic future, and primitivity.

    All sorts of children's cells exhibit these features compared to adult's.

    There is plenty of dishonesty, but there is also claims of dishonesty which are incorrect.

    Often the WHO, IAEA, etc. will state something like "no increase in cancer incidence is expected to be detected". Some people will call them liars because those people believe no level of radiation is safe.

    The WHO, IAEA, etc. mean that if one does an epidemiological study they don't expect to discern an increase in cancer incidence at the 90+% confidence level. That is an honest professional conclusion based on historic evidence. It depends on the doses, population size, etc.

    The people who don't believe any radiation is safe are (intentionally?) confusing absolute and relative safety. Eating is absolutely not safe, because there is a non-zero chance of food poisoning or choking. But relatively speaking, the benefits of eating outweigh the risks.

    The benefits of how we normally employ radiation (nuclear power, nuclear medicine, etc.) outweigh the risks. The anti-nuclear power folks rarely attack nuclear medicine, and they rarely attack other industries with poorer benefit to risk ratios.

    So what is motivating them?

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  3. Actually the WHO etc. reports are pretty good if you read them carefully. The misrepresentations arise in the media rendering and when interest groups run away with them. But that is not unique to this field, it happens, e.g., also with the IPCC reports.

    About why anti-nuclear power people rarely (ever?) attack nuclear medicine, perhaps it is because there, the trade-off is actually being made for every patient, with the patient having a say in it. The decision-making situation with nuclear power is rather different, with the benefits going to different folks than the risks. This motivates a lot of (often technically poorly informed, but genuine) distrust. My guess.

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  4. Yes, the WHO, etc. reports are very good.

    Folks have a say in nuclear plants. At the local level there are land-use commissions and at the federal level there is NRC licensing. At the state level there are energy commissions. They all accept public comment. Just because people have a say, doesn't mean the final determination will side with everyone...that's impossible. There are also risks to no nuclear power (no power has risks, as does fossil fuels, etc.).

    If public health is really the concern, then these people should be concerned about nuclear medicine. They should be concerned about physicians overdosing/underdosing patients, or ordering unnecessary CT scans. Or they should worry about heart disease which kills more people in the U.S. than anything else.

    It's not public health they're concerned with and not radiation.

    They are fixated on demonizing nuclear power, like some people are fixated on deifying it.

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