More about CT scans
So, Doctor Z – what’s this I hear about CT scans causing over 100,000 cases of cancer every year? I’m scheduled for a CT scan later this week – should I cancel?
Well…I read the paper and I’m not cancelling my upcoming CT scans – I had 5 last week, I have 5 next week, another 5 the week after that…one every working day until Sept 22. The reason? I’m undergoing radiation therapy and I’ve got three small gold markers placed around the tumor; the CT scan is used by the treatment software to make sure that the radiation beam is focused on the tumor as precisely as possible, obliterating the tumor over the course of the treatment without giving extra dose to the healthy tissues in the area. In my case the radiation exposure from the CT scans is justified because the risk from the CT is lower than the risk of the beam missing the tumor.
I had a CT before my appendectomy – in that case the risk from the CT was lower than the risk of being anesthetized and operated on needlessly. In fact, I’ve had a number of CT scans and every single CT I’ve had was taken for a medical reason and, in every case the risk of lacking the diagnostic information provided by the CT was greater than the risk from the radiation. For you – if your CT is one your doctor ordered to find out what’s might be wrong with you then you ought to have the exam; if you’re getting the CT because you’re worried and want to find out if there’s anything weird inside your body…usually not a good idea, regardless of the paper you’re asking about.
Having said that – let’s see what the paper itself says, shall we?
The authors note that, in 2023, over 60 million people in the US were exposed to slightly more than 90 million CT scans and that the radiation from these scans will probably cause slightly more than 100,000 people to develop cancer as a result of their exposure. That’s about…call it about one chance in 1000 that any individual CT scan will cause a cancer (if they’re correct) – a rate that’s lower than the risk of dying in a traffic accident. But here’s the thing – one definition of science is that it’s a system in which scientists make predictions (e.g. the number of extra cancer deaths from CT scans) that can be tested and found to be false. Given the background cancer rates – over a third of us will develop cancer and about a quarter will die of it – there’s no way to “see” those additional cancers – it’s like looking across a golf green, noticing one blade of grass that looks as though it might be a fraction of a millimeter longer than the others, and deciding that a nick on one of the lawnmower blades was responsible. But was it? Well…maybe – but will we ever be able to prove that a small nick on one lawnmower blade happened to cut that one blade of grass that might – or might not – be ever-so-slightly longer than the others…and that this is the only of several plausible reasons for the blade being longer? Of course not – that prediction cannot be tested and found to be false to a reasonable degree of certainty so it’s not a scientific statement – it’s a guess.
So, of those 60 million people we’d expect that close to 20 million will get cancer and 15 million or so will die of it. One hundred thousand additional cancers would bump those numbers up to 60.1 million and 15.1 million respectively – an increase of about 0.16% and 0.67% respectively. These are numbers that are lower than the normal variability from year to year – which means that the authors’ claims can’t be tested or falsified. They’re not based in science or statistics. And – get this – the authors acknowledge this when they say “To empirically quantify lifetime risk would require decades-long follow-up studies of very large populations.” Which makes sense – even if we could afford to do annual checks on 60 million people for up to 50 years and even if we saw a few extra cancers over that period of time the numbers would be far too small to be able to definitively state that they were even a real increase (rather than normal fluctuation) that could only be due to radiation exposure.
Of course, there’s also the fact that cancer rates have dropped fairly steadily while the number of CTs being taken has risen just as steadily. Not to mention that the radiation from CT scans can help to catch cancers and other health issues early enough to treat them successfully, saving people who might otherwise have died. The bottom line it that it’s a complicated issue – more complicated that the authors make it sound.
In my case, I have a pretty good understanding of the risks from radiation as well as what can happen if a doctor lacks the information needed to diagnose an illness. Or, to put in the terms of ALARA (keeping radiation exposure as low as reasonably achievable), we can ask ourselves “Is it reasonable to undergo exploratory surgery in order to avoid a rem of exposure?”
This is one of those topics where it’s very easy to get trapped in the rabbit hole, digging ever-deeper into any of the factors involved – but I’ll spare you! Having said that, there’s a nice discussion online written by a physician that bears reading, and that includes links to some interesting materials. But even without getting into all of that, I think the advice I gave earlier is still appropriate:
- If the CT was prescribed by a physician, it probably makes sense to have it done because the doctor is looking for diagnostic information to help make a diagnosis or to track the progress of your condition (whatever that might be).
- If the CT was not prescribed by your physician – if it’s something you just want (or think you need to) have, consider giving it a pass because the odds are that it’s not going to catch anything medically significant.
I hope this helps – and good luck!