I wasn’t worked up over the Tiger Woods story. In contrast, this story boils my blood.
This USA Today story concerns a cancer study that purports to prove that
CT scans deliver far more radiation than previously believed and may contribute to 29,000 new cancers each year, along with 14,500 deaths, suggest two studies in today’s Archives of Internal Medicine. One study, led by the National Cancer Institute’s Amy Berrington de Gonzalez, used existing exposure data to estimate how many cancers might be caused by CT scans.
Let me demonstrate how this statistic is also a lie, and on top of that, a damned lie.
- First, the study took the existing scientific data on radiation delivered by CT scans (measured using sensors on human-shaped dummies)… and completely disregarded it until the last step.
- Second, the study compared the amount of cancer afflicting the people who took the CT scans in the study, finding the level to be shockingly higher than in those who did not across various age and gender categories, etc.
- Third, the study took the level of cancer that occurred. Blaming CT scans for these cancer incidents, the researchers reverse engineered a number by declaring, Y amount of cancer resulted, so X amount of radiation must have been delivered by the CT scans, simply by using mathematics.
- Fourth, the researchers compared what the radiation must be (according to the study) to what the radiation has been measured to be via certified scientific instruments.
- Finally, the researchers have published their study at a time of great controversy for both CT scans and MRI’s, which are viewed by health care reformers as hugely expensive and over-used and a prime target for cuts in service to save the nation, and increasingly, the Federal government, cold, hard cash.
USA Today has run with this story, declaring that “based on those higher measurements, a patient could get as much radiation from one CT scan as 74 mammograms or 442 chest X-rays.”
Here’s the problem.
Let’s assume, for the sake of argument, that the amount of radiation measured by scientific instruments, i.e. empirical data once considered fact, is correct. This may be difficult, but as I said, it’s for the sake of argument.
Would the above study have proven the scientific instruments to be correct, even if they are measuring the actual proper level of radiation being delivered by CT scans?
Probably not, and here’s why:
THE ONLY WAY THE AMOUNT OF CANCER WOULD BE THE SAME IN THE STUDY GROUP AS IN THE CONTROL GROUP IS IF THE DOCTORS INVOLVED ARE ABSOLUTELY, ACROSS-THE-BOARD INCOMPETENT, AND NO BETTER AT PICKING AT-RISK PATIENTS THAN A PLACEBO.
That is, doctors are using their professional medical judgment to pick the people they believe are at a higher risk for cancer than other people in their age and gender. If the doctors are not complete idiots, the people who receive the CT scans are already more prone to cancer than the people who don’t, regardless of actually receiving the CT scan. Only if the doctors were a) wholly incompetent, b) randomly incompetent, not favoring low risk patients over genuinely at-risk patients, would the study reverse engineer a radiation figure similar to the real one, and that’s if the true radiation number is identical (or very similar) to that recorded by scientific instruments.
So what if the CT scans really do deliver more radiation than the instruments have said? Did the study take into account selection bias by the medical profession, i.e. discount the level of competence by the doctors? No, it did not.
Not all doctors agree about those risks. Scientists have not yet determined whether low doses of radiation really increase cancer risk, or if cancer risk goes up only after exposure levels reach a certain threshhold, says James Thrall, chair of the American College of Radiology.
He says it’s also tricky to compare cancer rates between people who’ve had CT scans with those who haven’t. People undergoing scans may have underlying health problems that predispose them to cancer, he says.
This study hits the presses at a politically sensitive moment. After the push to have mammograms for younger women clawed back, I had a sneaking suspicion that someone would go after CT scans just as MRI’s have been criticized. I didn’t make any predictions about what form that attack would take. I’m rather disgusted with this outcome.
Overnight, America will undergo a wave of discussion about “Killer CT Scans” and “CT Scans are Killing Us – Make It Stop” and so on and so forth. The actual USA Today headline is, “Radiation from CT Scans Linked to Cancers, Deaths“.
The only thing this statistic should be linked to is, in the immortal words of Mark Twain, lies and damned lies.