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BACKGROUND: Progenitors of the immortalized human glioma cell line, SHG-44, are significantly less sensitive to irradiation. Two hypotheses regarding the mechanism of this effect exist: several studies have suggested that there is a subgroup with different radiosensitivities in identical cell group, and the progenitors of irradiate is a adaptive response subgroup, so its radiosensitivity is descend. A second hypothesis suggests that irradiated glioma progeny have a stronger ability to repair DNA damage. This would suggest that when progeny are continuously irradiated, resistance to irradiation-induced DNA increases, and radiosensitivity decreases.OBJECTIVE: To investigate radiosensitivity and growth features after irradiation to progeny of the human glioma cell line SHG-44.DESIGN, TIME AND SETTING: A randomized, controlled experiment, which was performed at the Department of Radiology Laboratory, the First Hospital Affiliated to Soochow University, between September 2004 and January 2006.MATERIALS: The glioma cell line SHG-44 was provided by the Institute of Neuroscience, First Affiliated Hospital of Suzhou University. Propidium iodide reagent was provided by Coulter Corporation. A linear accelerator, KD-2 type, was provided by Siemens, Germany. The flow cytometer EPICS-XL was provided by Coulter Corporation.METHODS: Brain glioma SHG-44 cells were divided into four groups: SHG-44, SHG-44-2, SHG-44-6, and SHG-44-10. The SHG-44-2, SHG-44-6, and SHG-44-10 cells were vertically irradiated with varying doses of 2,6 and 10 Gy by a linear accelerator (6 MVX). The cells were passaged for 15 generations and cultured in RPMI-1640 culture media.MAIN OUTCOME MEASURES: Community re-double time, mean lethal dose (D0), extrapolation number (N), fraction surviving fraction irradiated by 2 Gy dose (SF2), quasi-threshold dose (Dq), and cell cycle.RESULTS: The Population doubling time (PDT) of SHG-44-2, SHG-44-6, and SHG-44-10 cell groups was not significant (P=0.052). Compared to these three groups, the PDT of the SHG-44 cell group was significantly difference (F=7.878, P<0.002). SHG-44 cell clone ratewas 26.5%, and SHG-44-10 cell group was 15.5%. The SHG-44-10 cell group also exhibited radiosensitivity, but was less than the radiosensitivity of the SHG-44 cell group. Compared to the SHG-44 cell group, the ratio of the G2/M phase was decreased in the SHG-44-10 cell group, and the radio of S phase was increased. The SHG-44 and SHG-44-10 cell groups were irradiated with 8 Gy. After 12 hours, the G2/M ratio was compared to pre-irradiation times, indicating a significantly higher ratio in the pre-irradiated groups (P<0.01). The cells between SHG-44 and SHG-44-10 groups were harvested 12 hours after irradiation: G2 phase of SHG-44-10 cells was arrested and the G2/M ratio was increased, which was intensified with increasing irradiation doses.CONCLUSION: In the present study, the proliferation delay and decreased radiosensitivity were confirmed in progeny of irradiated human glioma cells, and radiosensitivity was dose-dependent.