Influence of ionizing radiation on oxygen profiles in different types of multicellular spheroids

Human glioma (U-118 MG and U-138 MG), human colorectal adenocarcinoma (HT-29), human thyroid carcinoma (HTh 7), and hamster embryonic lung (V79-379A) spheroids were irradiated with either single doses of 16 or 40 Gy or fractionated doses of eight times 5 Gy. Oxygen profiles in the spheroids were measured with microelectrodes at different times following irradiation, and these profiles were then compared with the oxygen profiles measured in parallel cultured nonirradiated spheroids. No significant radiation-induced changes in the oxygen profiles were seen in any of the spheroids within the first few days after irradiation. The glioma spheroids did not show any significant increase in oxygen tension even after longer times; however, they were growth inhibited, and the number of S-phase cells was strongly suppressed. Increases in oxygen tension did occur in the HT-29 and V79-379A spheroids but only appeared more than a week after irradiation, when degeneration had started. Histological changes and decrease in diameter were seen in the spheroids that started to degenerate about 5 days after irradiation. Thus radiation doses in the therapeutic range did not, for the spheroids studied, produce rapid increases in the oxygen tension. When a change occurred, it appeared rather late and was probably a consequence of cell degeneration.