It is a truth never universally acknowledged in TV medical dramas that declarations on how long a terminally ill patient has left are something most doctors shy away from, given the real-world uncertainties.

But the need for a definitive prognosis is not just an issue for the script writers in need of a plot device.

It is also a legal issue in the context of Australia’s rapid embrace of voluntary assisted dying (VAD).

Three oncologists believe the laws underpinning the system need to be rewritten.