The prime goal is to alleviate suffering, and not to prolong life. And if your treatment does not alleviate suffering, but only prolongs life, that treatment should be stopped.
Source: In Macmillan Dictionary of Quotations, by John Daintith, 1989.
-- Christiaan Barnard, (Nov 8 1922-2001), South African surgeon; He performed the first human heart transplant operation.