The relationship between radiation effect and fraction number was studied in a case of metastatic lung cancer. Three radiotherapeutic fields were taken from multiple pulmonary metastatic foci of squamous-cell carcinoma from the lower jaw. The same total dose was given to each field with the same over-all time, but with three different daily doses. In each radiation field several nodular shadows of metastases were contained, one of which was measured for diameter periodically. Radiation effects

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... ere summarized in the formula: Where Ro is the tumor size before treatment, Rn is that after irradiation, t the interval of time between fractions, T the over-all time, and ƒ¿ and ƒÀ constants related to the daily dose.