Flight attendants have a higher risk of all types of cancers, finds study (independent.co.uk)

US navy nuclear operators receive less radiation per annum than any other average citizen. Working inside a metal ship next to a well-shielded reactor actually results in a decrease in exposure. Many common real-world tasks give you significant doses of ionizing radiation, like medical/dental x-rays and high altitude flights.

Cruising altitude is typically 30k-40k feet.