Individualization of Radiotherapy by Micronucleus Test

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A small difference of the radiosensitivity of tumor cells asserts great influence on the final control rate of tumors. Therefore, it is ideal that radiosensitivities of tumor cells and normal tissues could be examined before the start of radiotherapy, and dose fraction, total dose could be changed on each patient. We have examined the radiosensitivity in 14 different esophageal cancers cultured from surgical specimens The tumor cell suspensions were cultured and several days after, 50 KVp xrays were irradiated. Thereafter the culture was continued for 48 or 72 hours with cytochalasin B. This agent was added to identify the cells passed through mitotic phase after irradiation. Cytochalasin B inhibits cytoplasmic cleavage without interfering nuclear division. Therefore, such cells could be easily identified. The tumor cells were fixed and microslides for micronucleus assay were prepared. The micronuclei were observed by fluorescence microscope after staining with propidium iodide.The dose response curves of micronuclei were analyzed according to linear-quadratic model. The alpha/beta values among 14 esophageal cancers ranged from 1.5 to unlimited size. Alpha values differed more largely from tumor to tumor compared with beta values. Oxygen enhancement ratios (OERs) also ha wide range (1.3-2.7) especially in low radiation dose range (0-2 Gy). The differences in tumor cell radiosensitivity were clearly demonstrated.To examine the difference of normal tissue radiosensitivity in individual patient, we have studied that in 3 different strain of mice (Balb/C, A/J, C3H/He). The correlation between the radiosensitivity of lymphocytes determined by micronucleus assay and those of fibroblasts and intestinal crypt cells. The order of radiosensitiity of lymphocytes obtained in 3 different strain of mice was accurately repeated in those of fibroblasts and intestinal crypt cells.