LONDON: Millions of people who undergo routine health scans with radioisotopes are unwittingly going radioactive and risk triggering security scares at airports, scientists warned on Friday. Patients may remain radioactive for up to 30 days after being scanned or treated with radioisotopes, said a case report in the British medical journal The Lancet.

“As a result, patients are at risk of setting off radiation alarms at airports,” said Richard Underwood of London’s Brompton Hospital.

In one case in March last year, a 55-year-old commercial pilot had a thallium scan to check his heart and two days later travelled to Moscow as a crew member.

“While passing through customs, the radiation detector alarms were triggered and the patient was detained by airport security officers,” the researchers said. He was released later that day only after “extensive interrogation.”

Four days later, the pilot again set off an alarm in Moscow and was detained and relased. Airport officials gave him a special card to carry explaining his propensity for setting off alarms because of his thallium scan.

Initial reports of radioisotopes triggering radiation detectors appeared more than two decades ago, said Mr Underwood and his fellow researchers.

One patient set off radiation detectors in a bank vault three days after a thallium stress test, according to a 1988 report.

Two other patients were seized by the US Secret Service when they set off radiation alarms during visits to the White House, said another report in 1986.

“Stricter measures and more sensitive radiation detection systems are being deployed at airports worldwide,” Mr Underwood said.

“It is important to warn patients having had a thallium scan that they may trigger radiation detectors for up to 30 days.”—AFP