[Therapeutic ratio in radiotherapy--clinical analysis and strategy]

The purpose of this paper is to report the clinical analysis and radiation strategy for cancer in the therapeutic ratio (T.R.) which were decided on relationship between tumor lethal dose and tissue tolerance. T.R. was first described at 1936, 40 years after discovering X-ray, by Holthusen. It is the basic principle of Radiotherapy for Radiation Oncologist. Radiotherapy must be planned on basing T.R. which is decided after estimating tumor factor, normal tissue tolerance, and host condition. In recent years, not only early skin reaction but late deep organs effects should be considered on T.R. because radiation energy has become higher from KeV era to MeV. The Optimum radiation methods has been investigated according to consider T.R.