In the last half of the 20th century, when someone wanted to know how much annual radiation dose a typical person receives, it was easy to recall....360 mrem (close to the number of days in the year).
But things change and by the early part of the 21st century the average is 620 mrem! (I have no mnemomic for that).
The culprit for the increase was medical radiation exposures. People were living longer, enjoying more advanced medical technologies, doctors wanted to avoid misdiagnosis for tort reasons so they wanted more imaging, etc.
Now some cardiologists at the Mayo Clinic have revised how they do their cardiology, with an average dose reduction of around 40%. They are tracking patient radiation doses and opting for lower quality, but sufficient imaging.
By publishing their achievements others can mimic.