Now that's interesting - I hadn't heard of cancer radiation treatments being performed with proton and fast-neutron beams, which can indeed cause activation of the subject material. I was mostly guessing at cancer treatments, given the weird reference in the GP post to Chemotherapy. Certainly there are other treatments that do result in increased radioactivity of the patient after treatment.

Nevertheless, I would still find it pretty surprising if any of these sources could be reliably detected from inside a moving vehicle by a stationary sensor. Or that cases of these medical treatments would not be overwhelmed by other incidental sources of radiation being slightly higher or lower than usual.