If you are planning on travelling or going into a high security location, such as the Superbowl, and having any sort of radiation treatment, be ready to explain yourself to the security people. Since 9/11 the tools that security companies are using have improved significantly. They now pick up the trace radioactive particles used in medical proceedures for up to 30 days.
With the rising use of radioisotopes in medicine and the growing use of radiation detectors in a security-conscious nation, patients are triggering alarms in places where they may not even realize they’re being scanned, doctors and security officials say.
Nearly 60,000 people a day in the United States undergo treatment or tests that leave tiny amounts of radioactive material in their bodies, according to the Society of Nuclear Medicine. It is not enough to hurt them or anyone else, but it is enough to trigger radiation alarms for up to three months. via Yahoo! News.
My recommendation, if you are having any sort of radioactive treatment done and planning on traveling, have the doctor give you a letter explaining the proceedure and what radioactive material is being used. This may make your trip through security go much smoother.