The paradox of adaptive responses and iso-effect per fraction.

While the iso-effect per fraction assumption would preclude the observation of adaptive responses for cells survival after radiotherapy fractions, this does not preclude the observation of adaptive responses for other endpoints. Adaptive responses for cell survival might also manifest without invalidating the iso-effect principle in practical terms. It may also be the case that instances of both phenomena can be observed under different conditions, but not at the same time.