Relations between-age atoccupational exposure to ionising radiation andcancerrisk

Objectives-To discover how theage whenagivendoseofionising radiation is received (exposure age)affects thesubse- quentcancerrisk, andwhether thetypes ofcancercaused byrepeated exposure to smalldosesduring adultlife differ from naturally occurring cancers atthatage. Method-A nestedcase-control design withallpossible controls ina cohortof nuclear workers, andaMantel-Haenszel test(requiring onlyonedegreeoffree- dom)todiscover whethertherewasany levelofexposureagewherethenull hypothesis ofnoeffects ofradiation was rejected. Thisanalysis wasfollowed by inspection ofhowdifferent typesofcan- cerswererelated tothecancerrisk. Results-For radiation received atleast 15yearsbefore a cancerdeath(toallow forcancerlatency) evidence ofa dose related riskwasfoundwhichwaslargely theresult ofexposures during thelast10 yearsofworking life (between 55and65 yearsofage).Therelative frequency of sitespecific cancersshowednosigns of beingdifferent forradiogenic andidio- pathic cancers, andthere wasnoevidence oftheexceptionally strongassociation between radiation andleukaemia foundin atomicbomb dataandotherhighdose situations. Conclusions-Sensitivity tocarcinogenic effects ofradiation increases progres- sively withageduring adult life and,pro- videdthedoseistoosmalltoproduce manycell deaths, theratio ofleukaemias tosolid tumoursisnodifferent forradi- ogenic andidiopathic cancers.