To move from diagnostic to therapeutic nuclear medicine, however, requires a major increase in the level of radioactivity on any targeting material so that it will destroy the tissue in which it concentrates. Where this can be done cleanly, it has the distinct advantage of sparing uninvolved normal tissue from any damage. For example, radioiodine in therapeutic doses has been used for the treatment of hyperthyroidism in functioning thyroid cancers since the late 1930's. The advent of specific radioactive monoclonal antibodies has stimulated many clinical trials in the field of cancer therapy. In addition, there are agents that concentrate in bone, such as radiostrontium, which are being used for the control of pain in patients with bone metasteses from cancers of the prostate and breast.
Nuclear medicine is a constantly and rapidly changing discipline.
Such advance directives now have legal support in Quebec, and are known here as ''mandates''. They are still used by some, but here in Quebec living wills make no provision for the naming of a proxy and have no legislation supporting them. The second generation of advance directives or mandates constitutes, in principle, a major advance and improvement over living wills. They no longer apply only to the terrninally ill or only to directives about terminal, critical or life-supporting care. The earlier pre-established living will formulas were often written in too general or ambiguous terms to be accurately interpreted by health care professionals faced with a decision.