The sensitivity of tumor to chemotherapeutic agent depends on tumor size, as has been reported previously by several authors. To estimate the difference in the effect of combination of chemotherapy and radiation therapy along the tumor size,
cyclophosphamide and radiation (under champ hypoxia) was given to 3 day old tumors after transplantation of 1,000 cells(microscopic tumors) and 6mm tumors(gross tumors) of FSa II growing in the leg muscle of C3Hf/Sed mice.
TCD50/120 was 48.5(95% CI: 46.5-50.7) Gy and 81.7(95%(CI: 77.7~80.8) Gy for 1,000 cell tumors and 6mm tumors, respectively, When combined with cyclophosphamide, TCD50/120 was reduced to 31.0(95% CI:27.4~35.1)Gy and 75.5(95% CI:71.6~79.5)Gy,
respectively.
The estimated dose modification factor was 1.56 for 10* cells and 1.08 for 6mm tumors. Dose reduction was 17.5 and 6.2Gy and these corresponds to 1.40 and 0.49 log cell kill9estimated from Do) for 10* cell tumors and 6mm tumors, respectively.
As a result, the effect of cyclophosphamide given prior to irradiation was 2.8times more effective in 10* cell tumors than 6mm tumors.
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