The ongoing CT debate

Slow day and a slow night at work.  Found some articles worth posting and comments.

This is a brief comment from Dr. Elliot Siegel about the proposal by some to require informed consent for the radiation exposure associated with CT. 
Dr. Siegel's comments

Personally, like the recording of every dose, I think requiring a signed informed consent unecessarily exaggerates the risk of the radiation. I particularlly like his comment about the use of the LNT based  Japanese survivor studies, which assumes all delayed toxicity from a nuclear explosion is due to radiation.  I believe this is another bias of the BEIR reports, which are done by radiation protection specialists.


Just this month an interesting, and very relevant study came out of Harvard showing that the riks of cancer from CT scans in young adults is far less than the risks of the diseases for which the scans were done.  This type of study makes far more sense to me than just using the LNT to calculate inflated risks.  And, the Harvard study uses CT risks based on the LNT, which means the relative risks of the CT scans is even lower than the study suggest.
press release for Harvard study.



Here is a study about the risks of radiation induced cardiovascular disease. This study looks at multiple radiation studies previously published, including low dose exposure in radiation workers as well as the Japanese survivors.
cardiovascular disease

I find this paragraph particularly interesting.

"Most of the studies considered in the present review involved low-to-moderate mean cumulative radiation doses (≤ 0.2 Gy), with participants in the occupational studies exposed at near-background dose rates. Nevertheless, the small numbers of participants exposed at high cumulative doses (≥ 0.5 Gy) drive the observed trends in most cohorts with these higher dose groups."

In other words, if you take out the data from the Japanese bomb victims, the data really is weak.  Here again the assumption is that all delayed toxicity and morbidity from the explosions is due to radiation, ignoring all the other effects of an atomic bomb.



Here is an excellent discussion of why the LNT is no longer a reasonable assumption when assessing radiation risks.  This is not to say there is no risk, just that the risk is not linear, and very low compared to other risks in our daily life. (see page on Risks.)
Paper on LNT from Radiology.

Here is a companion article in the same issue of Radiology giving the opposing viewpoint, that the LNT is the best we can do in assessing radiation risks at low levels.
Paper defending the LNT in Radiology
My favorite line in this paper, " Just because one cannot detect a risk does not mean that it is not there."



The question here for me is, what is the goal, and at what cost? The proponents of the LNT want us to go to great extremes to protect the population from the very small risks of low dose radiation.  The anti-nuclear energy folks want us to burn more fossil fuels and polute the environment on a daily basis, to avoid the miniscule potential risk of radiation exposure.  If the goal is to save lives, just lower the national speed limit to 25 mph.  This will save lives and energy.  Plus, it is free and good for the environment.  Or better still, have the government stop subsidizing and promoting our high carb, low fat/protein diet, which has been clearly shown to be the major factor in our national epidemic of obesity, diabeties, metabolic syndrome and heart disease.

But, the goal here is not to save lives.  The goals here are far more complex, and complicated by multiple factors.  As always, the biggest single factor is money.

Radiation protection is a multi-billion dollar industry.  The fact that every life saved costs millions of dollars is not seen as a problem to those within the industry.  Environmentalists raise lots of rent money capitalizing on radiation phobia, so no radiation is safe.  And, both the food industry and the transportation industry are major forces in American economics and politics.  They will not willing accept changes which cost them money .

Much ado about (almost) nothing

In the June Lancet Dr Mark Pearce, et al. published an article, "Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumors: a retrospective cohort study." full article and a comment.

In the November issue of Radiology, Drs Brenner and Hall, both radiation physicists of some renown, published an editorial referring to this article entitled, "Cancer Risks from CT scans: Now that we have the data, what next?" full editorial

It is a catchy title for an editorial, but the problem is we still don't have the data.  The study by Pearce, et. al. compares the long term followup of children who have no CT scans vs kids with a low number of CT scans vs kids who have several CT scans, and looks at the incidence of brain tumors and leukaemia.  It is a large study with some 180,000 children included.  What is not included is why they got imaged in the first place, as this could not be extracted from the database.  They conclude, and of course Drs Brenner and Hall agree, that the CT scans caused the tumors.  What they actually proved is that kids who require multiple CT scans are sicker kids. 

Every physician with any experience knows that some people are just more disease prone.  In the old days of film radiology, these were the patients with the thick jackets.  Now they are the patients with the long problem lists in their electronic medical record. When I was an intern we called it PPP (piss poor protoplasm.)

The study retrieved data from national registries on children who had CT scans before the age of 22.  They then retrieved data from cancer registries for two diagnosis, leukemia and brain tumors.  They did not look at other diagnosis.

I would be willing to bet there is a long list of diagnosis which are statistically different in the three groups.  They need to analyze the data for the incidence of things like intestinal disorders, pneumonia and chronic pain in these children down the road.  No doubt these problems are more frequent as well.  Did radiation cause them all?  They want to believe the CT scans caused the cancer, but they have used selection bias to divide their study groups.

Just another example of researchers wanting to support their preconceived beliefs.