X-rays and CTs and Treatments – Oh My? Why our medical radiation exposures are OK
Hi, Doctor Z! So I got a question for you. I heard recently that we’re getting a lot more medical radiation now than in the past and most of our radiation exposure is from medicine – x-rays, CT, nuclear medicine, radiation therapy, MRI, and all that. Shouldn’t all this radiation be bad for our health? So how come everyone in their 70s, 80s, and 90s doesn’t have cancer?
You know, that’s a really good point – and you’re absolutely right. Before x-rays were discovered in 1895 the average exposure to medical radiation was 0 rem and the average life expectancy was about 45 years; with the exception of a dip in 1918 (from the deaths in World War 1) and 2021 (when COVID killed so many) the average life expectancy in the US has climbed steadily higher decade after decade to a little more than 79 years today. And in this same time frame, exposure to medical radiation has also increased steadily – in the 1980s the average American received about 50-60 mrem from medical radiation while, today, that exposure has climbed to about 300 mrem – five or six times as much. So – yeah – if every bit of radiation is bad for our health, why hasn’t this huge increase in medical radiation exposure caused a cancer epidemic? And it turns out there’s no quick and simple answer, so bear with me.
The biggest part of the answer is that there’s more than radiation that affects our lifespans. In 1895 a lot of people died from infectious disease because there weren’t any antibiotics and a lot of physicians didn’t know (or didn’t believe) that microbes could make us ill. This was also a time when drinking water wasn’t necessarily safe to drink, food-borne illness was fairly common, and in the pre-vaccination and pre-antibiotic era, a lot of people of all ages died from ailments that are rare today. Most of the extension of our life expectancy can be explained by vaccines and antibiotics, and other improvements in public health – improvements significant enough to more than outweigh a small added risk from medical radiation.
But let’s think about medical radiation itself – the average exposure might be 300 mrem per person per year, but how many of us actually receive that exposure? Just this year, I had about 30 CT scans, a few nuclear medicine procedures, and radiation therapy for prostate cancer – along with x-rays of hands, hips, and knees. All of this exposed me to somewhere in the vicinity of 10 rem in just one year – about 30 times as much as my exposure to all other sources of radiation combined, including the radioactive sources I work with. In general, my exposure to medical radiation was at its lowest when I was young and it remained low until I was in my 50s; since then it’s been climbing steadily…and I’d expect that the story’s pretty much the same for most of us. Without public health and medical science humans seem to have an average life expectancy of between 40-50 years, and most people don’t receive much medical radiation in the earlier years; with the best of medical science and public health that seems to be pushed to upwards of about 80 years, which are the decades that our need for medical radiation skyrockets. Ironically, our increasing exposure to medical radiation helps us to live longer to receive even more medical radiation.
Thinking about it a bit – it makes sense that medical radiation would help to extend our lives; that’s why the doctors are telling us to receive it. When I came back from a trip overseas and was having trouble breathing and had lost a lot of weight it was a CT scan that showed I had pneumonia and not cancer. And, sure, there were other ways to figure that out, but the CT was faster, provided more information, was more definitive, and could be used to not only diagnosis pneumonia but, simultaneously, to rule out cancer and other alternatives – all for only about a rem of exposure! Would the pneumonia have killed me? Probably not – but there’s no way to know for sure…but I’m still here, two years later, in my mid-60s with every expectation to last another few decades.
If you’ve been reading this blog for more than a month then you might remember I got a whopping dose of radiation from my recent…shall we say “disagreement”?…with prostate cancer. In amongst all of the biopsies and MRIs (oh – I should also note that MRIs don’t involve ionizing radiation at all) I had a PET/CT scan, which exposed me to radiation both internal (the PET part) and external (from the CT), so I picked up over 2 rem from that scan, which was used to see if the cancer had metastasized. And the radiation therapy itself delivered about 7000 rem to the tumor with a whole-body dose of about 8 rem. So, all in, I received about 10 rem or so of whole-body radiation exposure because of my prostate cancer. And let’s face it, I’m not sure if the cancer would have spread enough to be fatal – most prostate cancers never get to that point. But the changes it was undergoing made it more likely to do so, and even the genetic testing done at the start showed a 5-10% chance that the cancer would spread and prove fatal in the course of a decade. So I’m willing to conclude that the dose I received was for a good cause; I’d make the same decision again.
The bottom line is that our society is aging and older people receive more medical radiation for both diagnosis and treatment. Add to that the fact that there’s a latency period for radiation-induced cancers – usually a few to several decades – and we can see the answer to your question: Public health and medical science have extended our lives into years that call for more medical care, which includes radiation exposure for both diagnostic and therapeutic purposes. This radiation might induce cancer a few decades later, but it can also reveal the presence of cancer early enough to be treatable. Thus, medical radiation exposure most likely adds significantly more years to our lives than it takes away.