Effect of growth rate of monolayer cells on survival after fractionated irradiation]

This study was performed to determine the effect of the growth rate of monolayer cells on survival following fractionated irradiation. HeLa and RMUG cells that had different radiosensitivities and growth rates (Do value: 2.3 vs 1.5 Gy, doubling time: 17 vs 46 hours) were irradiated with 2 Gy every day. The fractions surviving after fractionated irradiation were compared with those given single doses. The dose modifying factor for fractionated irradiation was larger in RMUG than HeLa: 1.7 and 1.2, respectively. Two clones from ADGU cells that had the same radiosensitivity but different growth rates were also given fractionated irradiation, but there was no difference in surviving fractions. When recovery following two split doses was determined in each type of cell, the results of the fractions surviving after fractionated irradiation were correlated only with recovery between split doses. These suggest that the growth rates of monolayer cells may not modify the fractions surviving after fractionated irradiation, and the monolayer cell system is not suitable for determining the effect of growth rates on survival following fractionated irradiation.