Radiation is not your friend

It’s one of the cruel ironies of medicine that the same radiation used to diagnose and treat cancer can also cause it. A new study from the National Cancer Institute estimates that CT scans done in 2007 alone will trigger 29,000 cancers and 15,000 cancer deaths—roughly equivalent to the number of Americans who were murdered last year. How’s that for guilt by association?

Several months ago I became concerned enough about my cumulative exposure to x-rays that I contacted a radiologist friend to ask his opinion. He reassured me that given the reason why I was being prescribed CT and PET scans, I shouldn’t worry about it. The threat of new cancer caused by radiation exposure is far less than that posed by the cancer I already have. The course of my disease needs to be closely monitored, he said, and radiation exposure is a necessary byproduct of that process.

I’ll admit that seeking a radiologist’s opinion on the risks of radiation is like asking a butcher if it’s safe to eat bacon and sausage. In either case, you shouldn’t expect total objectivity.

I’ve had more than a dozen CT and PET scans (plus MRs of the brain) based on the assumption that it’s worthwhile to detect metastatic cancer in my body early. Given how long most cancers are present before they’re seen radiographically, “early” becomes a relative term. Catching a met when it’s smallish as opposed to largish is perhaps a better way to put it. And even then, it’s debatable as to whether a patient with recurrent cancer actually lives longer when a cancer is found by CT or PET, and intervention can be planned. Where one met or more are visible, others often go undetected because they’re simply too small to be picked up. That’s called subclinical disease. Finding the bigger ones early does not necessarily stave off one’s date with destiny.

I used to live and breathe all this radiology stuff back in the day, when it was mostly theoretical knowledge. I wrote a couple of editorials in the early ‘90s for Diagnostic Imaging, in which I argued that x-ray exams might be safe, but could certainly be made safer. Some of our radiologist readers, and especially our advertisers, got goosey every time I used the word “overexposure.” Officially, most radiology facilities adhere to the ALARA principle, in which radiation levels are set “as low as reasonably achievable” for a good diagnostic outcome. Meanwhile, the FDA is currently investigating more than 200 claims of scan-related radiation overdoses in California and elsewhere. Apparently, not everyone has patient welfare as their top priority.

CT scanners and fluoroscopy devices use less radiation today than they did 20 years ago, but the number of CT scans in particular has exploded since then—about 62 million last year. You are exposed to a small but measurable risk every time you slide through the gantry of a scanner and are bombarded with radiation. If it helps you to feel any better, you may want to visit xrayrisk.com where you can calculate your additional cancer risk based on your history of imaging procedures. If it’s true that my lifetime risk of cancer was about 45% on the basis of being an American male (before I was diagnosed), I’ve added at least 0.5% to that figure with all my diagnostic workups. That’s not a trivial increment.

Some doctors and medical centers track their patients’ total scan count, a practice that some day may become universal when electronic medical records are the norm. Until then, most of us are on our own. I may lose sleep worrying about my scans, but not because of radiation exposure. I’d love to have such a theoretical risk as my top concern.