[ RadSafe ] Traveling After Nuclear Medicine Procedure May Not Fly

[Susan Gawarecki]

Traveling After Nuclear Medicine Procedure May Not Fly
http://www.medpagetoday.com/Radiology/GeneralRadiology/tb1/1403  

By Michael Smith , MedPage Today Staff Writer
Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University of 
Pennsylvania School of Medicine.

LONDON, July 21-The threat of terrorism has made it tougher for patients 
who have undergone radioisotope procedures to slip quietly past 
radiation detectors deployed in airports and many other public places.

A 55-year-old commercial pilot learned that the hard way, when he was 
detained for questioning at Moscow's airport two days after having a 
thallium-201 myocardial perfusion scintigram.

After "extensive interrogation," the pilot was released, only to trip 
radiation detectors again four days later while leaving Moscow, 
according to a case report in the July 23 issue of The Lancet.

The case and others like it suggest "it is important to warn patients 
having had a thallium scan that they may trigger radiation detectors for 
up to 30 days," wrote Richard Underwood, M.D., and colleagues of 
London's Royal Brompton Hospital.

In fact, the authors suggested, it should be standard practice to give 
patients an information card after they've had diagnostic or therapeutic 
procedures involving radioisotopes.

The card would give:

    * The date and place of the procedure.
    * The radioisotope used and its half-life.
    * The potential duration of radioactive emissions.
    * Who to call for verification.

More than 18 million such procedures are carried out every year and more 
and more radiation detectors are in place in what the U.S. Nuclear 
Regulatory Commission calls "critical infrastructure," including 
airports, banks, railway stations, and highway tunnels.

In 2003, the commission urged that nuclear medicine specialists make a 
point of emphasizing that patients should follow the written 
instructions they get after a procedure, which usually suggest not using 
public transport within two days.

The recommendation came after a New York State police pulled over a bus 
traveling from New York to Atlantic City after it tripped a radiation 
detector in a highway tunnel leading out of the city.

It turned out that one of the passengers had received a dose of 
iodine-131 earlier the same day, but had ignored her doctor's written 
suggestion to avoid public transit for at least two days.

To "avoid unnecessary concern by law enforcement authorities," the 
commission suggested nuclear medicine specialists should "consider" 
giving patients their business card and written information about the 
procedure.

A spokesman for the commission said there's no legal requirement to 
report such events, so the commission doesn't know how common they are.

But reports date back to at least 1986, when a letter to the New England 
Journal of Medicine noted two incidents in which Secret Service agents 
seized patients who set off radiation detectors at the White House after 
thallium stress tests.

The half-life of thallium-201 is 73 hours; the usual intravenous dose is 
80 mega Becquerel. That means, wrote Dr. Underwood, that patients may 
trigger radiation detectors for at least two weeks.

In fact, highly sensitive modern detectors -- like those issued to 
police and other security personnel -- may detect the traces of 
thallium-210 for as much as a month, according to a report at the 2004 
meeting of the Radiological Society of North America.

The least durable radioisotope was fluorine-18, which lasted about a 
day; the most durable was iodine-131, which in some cases could still 
trigger detectors 95 days after it was administered.

The pilot -- who had never complained of chest pain or shortness of 
breath -- was shown to have a dilated and hypertrophied left ventricle 
with no evidence of inducible ischemia, the authors noted.