You miss the point. Studies on low level radiation effects study, for example, deviations from the linear model, but are so far inconclusive, because it is hard

You miss the point. Studies on low level radiation effects study, for example, deviations from the linear model, but are so far inconclusive, because it is hard to prescribe and control the level of radiation over such a long time. It could be done in lab, but who would subject themselves willingly to regular blasts of radiation? Radiation intensity in planes varies a lot, depending on the height, time of flight, geographical location, etc., so little can be inferred. It would take decades and lots of volunteers willing to get harmed in the name of science to do such studies reliably. Do you know of any such study?