Reoxygenation after single irradiation in rodent tumors of different types and sizes

Abstract

To investigate the variation of reoxygenation patterns after single irradiation in murine tumors of different types and sizes. Whole-body single irradiation of 13 to 15 Gy was delivered to 10 mm RIF1 tumors of C3H/He mice, 22 mm SCCVII tumors of C3H/He mice, and 16 mm EMT6 tumors of Balb/c mice. Thereafter, changes in the hypoxic fraction with time were determined by the paired survival curve method. The data were compared with the results we had ++previously obtained with 10 mm SCCVII and 10 mm EMT6 tumors. The hypoxic fraction at 1 h after the priming irradiation was 26% for 10 mm RIF1 tumors, 48% for 10 mm SCCVII tumors, and 100% for 10 mm EMT6 tumors. Thus, RIF1 and SCCVII tumors, both of which have few necrotic areas, showed rapid reoxygenation, whereas EMT6 tumors, which have large necrotic areas, reoxygenated slowly. Although the hypoxic fraction returned to the pretreatment level within 72 h in 10 mm SCCVII and 10 mm EMT6 tumors, it did not in 10 mm RIF1 tumors. In contrast, the patterns of reoxygenation were similar between 22 mm and 10 mm SCCVII tumors and between 16 mm and 10 mm EMT6 tumors. The three tumors showed different patterns of reoxygenation. Tumors that have a low proportion of necrosis may reoxygenate rapidly. However, tumor size appeared to have less influence on the pattern of reoxygenation.