WASHINGTON  Doctors told Ann B. Maddox that she had thyroid cancer and that the cure was to swallow radioactive iodine, to kill the malignant cells. She traveled 500 miles from her home in Fayetteville, N.C., for treatment at Johns Hopkins Hospital in Baltimore.

Then began a problem: what do you do when you cannot go home and you are radioactive?

There are about 40,000 new cases of thyroid cancer a year, and most patients are treated with radiation, which makes them potentially dangerous to people around them for up to a week.

The question of where they should spend that time is drawing new concern from doctors, public health officials and regulators.

In 1997, the Nuclear Regulatory Commission dropped a requirement that such patients be quarantined in the hospital. Instead, patients can be released right after their treatment, when they are at their most radioactive.