You have to be up to date on the exposure of a "chest xray" because tech improvements have considerably changed this in our lifetimes.

And cultural references can be dramatically and wildly off.

  "Plant director Bryukhanov reports no more than 3.6 roentgen, which I'm told is the equivalent of a chest x-ray, so if you're overdue for a check-up…"
  – HBO Chernobyl