I know of three cabin crew members who have suffered from DVT while or after flying very long range sectors e.g. SIN - LHR.
Theses individuals may well have a genetic susceptibility to this condition,
More research into crew related DVT should take place.
3 crew out of the relatively few crew I know is a lot !!
Mind you I also have a friend who got a DVT riding his sports motorbike on a touring holiday !!!