Hi!
I did a little google search and found these two refences to studies that both link the occurrence of cancer among pilots to the frequent disturbance of the biological rhythm of the body rather than to the higher radiation levels:
http://news.bbc.co.uk/1/hi/health/645113.stm
and
http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract
Greetings, Max