PREOPERATIVE VS. POSTOPERATIVE IRRADIATION; COMPARISON IN AN EXPERIMENTAL ANIMAL TUMOR SYSTEM

1. A comparison was made of the effectiveness of preoperative or postoperative irradiation in the improvement of surgical cures on a group of C₃H mice bearing a transplanted 6C₃HED Gardner lymphosarcoma.

2. Radiation therapy given before or after the resection of the tumor significantly enhanced the probability of tumor cure in comparison with the operation alone.

3. Preoperative irradiation, at dose levels below 2,000 rads, was significantly more effective in preventing tumor recurrences than comparable postoperative doses. However, this difference was not detected with doses above 3,000 rads.

4. The incidence of local failures was very high in the animals treated with resection of the tumor alone or low doses of postoperative irradiation. This is felt to be related to a smaller fraction of tumor cells in the marginal tissues being inactivated by postoperative irradiation as compared to preoperative therapy.

5. These experiments, particularly at low doses of radiation, confirm the dictum "Whenever postoperative irradiation is necessary, preoperative irradiation should have been given."¹⁵

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