A CT scan has a 1 in 1,000 chance of causing cancer (0.1%). But when you apply that to the whole U.S. population, you get a potentially large number of cases, even though most CT scans are harmless.

But it's also a good reminder not to get scanned more than is medically necessary. Prostate cancer patients probably don't need a PSMA-PET or regular CT contrast scan every year, for example, unless there's other evidence that their cancer is changing.