Radiosensitivity and cell cycle redistribution of cultured human tumour cells during fractionated daily 2-Gy irradiations.
Exponentially growing SQ-5 human lung squamous cell carcinoma cells were irradiated in vitro at 2-Gy per fraction per day continuously for 14 days. The number of total cells continued to increase exponentially till day 5, and reached a plateau level thereafter. The cell cycle distribution changed marginally for the first 5 days, and showed a prominent G2/M accumulation at day 7. Plating efficiencies decreased exponentially with increasing fractionation while the total clonogenic cell number remained constant until day 4. Radiosensitivity at each fraction was stable until day 9, but significantly increased at day 11. A comparison of plating efficiencies between the immediate and 24-h delayed assays revealed that the capacity of cells to spare 2-Gy damage increased with the number of 2-Gy fractions. These results suggest that sublethal damage could accumulate during multifraction daily irradiations, while repair of potentially lethal damage and/or proliferation could rather increase.
Division of Clinical Research, National Institute of Radiological Sciences Chiba, Japan.
T
T
Aruga
K
K
Ando
M
M
Iizuka
S
S
Koike
K
K
Fukutsu
H
H
Itsukaichi
N
N
Arimizu
D002294:Carcinoma, Squamous Cell; D002452:Cell Count / Q000528:radiation effects; D002453:Cell Cycle / Q000528:radiation effects*; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects*; D005434:Flow Cytometry; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms; D013997:Time Factors; D014407:Tumor Cells, Cultured