More than half of Ontario doctors are planning to retire or considering that option in the next five years, according to a new survey that underscores the challenges for the health system as baby boomer physicians approach the end of their working lives. The Ontario Medical Association released the results of an online survey of physicians on Wednesday that found 51 per cent of specialists and 52 per cent of primary care doctors identified themselves as approaching retirement age and either thinking of or planning to hang up their stethoscopes within five years.