Tests pose ra­di­a­tion risk – US re­search

Ex­perts fear tech­nol­ogy may be used un­wisely

Weekend Argus (Saturday Edition) - - LIFE -

AMER­I­CANS may be re­ceiv­ing too much ra­di­a­tion from med­i­cal tests whose value has not been proven, re­searchers re­ported this week in the New Eng­land Jour­nal of Medicine. More than two-thirds of Amer­i­cans un­der­went at least one such imag­ing pro­ce­dure in the three years cov­ered by the study, re­ported Dr Reza Fazel and col­leagues at Emory Uni­ver­sity School of Medicine.

The two big­gest con­trib­u­tors to the ra­di­a­tion ex­po­sure are CT scans, which use a se­ries of X-rays to pro­duce a three­d­i­men­sional im­age of the body, and heart per­fu­sion scan­ning to mea­sure blood flow through the ar­ter­ies lead­ing to the heart. In that test, ra­dioac­tive tech­netium-99m is in­jected into blood ves­sels and its progress through the heart is mon­i­tored with ex­ter­nal ra­di­a­tion de­tec­tors.

Ra­di­a­tion is known to cause can­cer, typ­i­cally years af­ter ex­po­sure. By some es­ti­mates, med­i­cal test­ing ra­di­a­tion con­trib­utes 2 per­cent of all can­cer cases, but ex­perts fear that it may be higher in the fu­ture as more pa­tients are ex­posed to th­ese rel­a­tively new pro­ce­dures. They are also con­cerned be­cause in­creas­ing num­bers of tests are be­ing per­formed on younger peo­ple, which al­lows more time for tu­mours to de­velop, and on women, who nor­mally live longer than men.

Some stud­ies have sug­gested that the grow­ing num­ber of CT scans be­ing per­formed re­sults in part from own­er­ship of the ma­chines by physi­cians, who may view them as a new profit source and pre­scribe un­nec­es­sary tests.

There is also a grow­ing in­ci­dence of whole-body CT scans in which physi­cians check for any signs of po­ten­tial dis­ease in healthy in­di­vid­u­als.

Such scans were not in­cluded in the re­port be­cause they are not cov­ered by health in­sur­ance.

The re­searchers stud­ied med­i­cal records of 952 420 adults be­tween the ages of 18 and 64 who were in­sured by United Health­care plans in Ari­zona, Texas, Florida and Wis­con­sin. Be­tween 2005 and 2007, 655 613 of the adults un­der­went at least one pro­ce­dure that ex­posed them to ra­di­a­tion.

The mean dose of ra­di­a­tion was 2.6 mil­liSiev­erts (mSv), a rel­a­tively low dose. A dose of 3 to 20mSv is con­sid­ered moderate, from 21 to 50mSv is con­sid­ered high and a dose over 50mSv is con­sid­ered very high. Fed­eral reg­u­la­tions put the max­i­mum an­nual safe dose at 50mSv.

Car­diac stress test­ing was the pro­ce­dure that ex­posed pa­tients to the high­est ra­di­a­tion lev­els, an av­er­age of 15.6mSv, and ac­counted for 22 per­cent of all ra­di­a­tion ex­po­sure.

A mam­mo­gram – a sin­gle X-ray – pro­duces about 0.4mSv. If the find­ings are ex­trap­o­lated to the en­tire pop­u­la­tion, more than four mil­lion Amer­i­cans are re­ceiv­ing a dose greater than 20mSv each year, the au­thors said.

“It is im­por­tant to note that we are talk­ing about ra­di­a­tion doses that are in­curred in one year,” said Dr Brah­ma­jee Naliamothu of the Uni­ver­sity of Michi­gan, se­nior au­thor of the study. “Cu­mu­la­tive doses over a life­time may be much higher.”

Dr Michael Lauer, di­rec­tor of the divi­sion of preven­tion and pop­u­la­tion sciences at the Na­tional Heart, Lung and Blood In­sti­tute, said de­spite the wide use of nu­clear per­fu­sion for car­diac imag­ing, there is no ev­i­dence that it in­creases sur­vival. – Los An­ge­les Times

PIC­TURE: AP

HOT TOPIC: Work­ers place a hoard­ing with the world map be­fore the start of a press con­fer­ence in New Delhi, In­dia, to mark the hun­dred days count­down to a cli­mate change sum­mit in Copen­hagen.

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