At one time, Concorde crews received the highest routine dose of any industry including Nuclear Reactor charge face workers. Fortunately the inverse square law works wonderfully well to prevent crews of 'ordinary' airliners at a mere 42,000 ft, from receiving anything more than a dose at the top end of 'acceptable background radiation'.
A holiday in Cornwall or a week or two in Aberdeen would put my radiation film badge - not actually a film any more, it's a TLD (Thermo Luminescent Dosimeter) - into the 'inquiry' region. Although my day job often involves working with x-ray equipment, I am not routinely expected to absorb any more than background for the general public and it has always surprised me slightly that flight crews are not obliged to wear the same TLD that I do. Inverse square law notwithstanding.
Monitoring your radiation dose by extrapolating from your 'at altitude hours' is okay, up to a point. Coronal flares and changing solar activity makes a substantial difference to the dose at altitude and the ISL can only do so much.
Roger.