Traveling after radiation
 

I read in Newsweek [August 25, 2008] that patients who have had recent radiation treatments should carry a doctor's note if they are going to cross into the U.S. from Canada or Mexico. The monitors used at border checkpoints can reportedly be triggered by nuclear isotopes leftover from these treatments.

Simple procedures like dental X-rays would have this effect for only about a day, but more serious treatments, like radiation for cancers or during transplants, could trigger the sensors for weeks after treatment.

Some hospitals are now issuing notes about this routinely. Carrying a doctor's note sounds a lot easier than getting questioned about why you set off alarms when crossing the border, so I'm passing along the tip.