Effects of the alpha-particle emitter At-211 and low-dose-rate gamma-radiation on the human cell line Colo-205 as studied with a growth assay.
BACKGROUND
The aim of this study was to investigate the biological effect of the alpha-particle-emitting isotope astatine-211 on the human cell line Colo-205 and to compare it with that of low-dose-rate gamma-radiation.


METHODS
Plastic (PMMA) rotating phantoms were constructed, allowing precise dosimetry on a cellular level for both types of radiation. Growth assays using 96-well plates were used to estimate apparent cell survival for the two types of radiation. From this, the relative biological effect (RBE) could be estimated.


RESULTS
Irradiation of the cells with 211At resulted in an RBE of 25.1 +/- 6.7 at 37% survival, and 17.3 +/- 2.5 at 10% survival, when compared with low-dose-rate gamma-irradiation. The absorbed dose at 37% survival, 0.12 Gy, corresponds to 2.2 traversals of alpha-particles through the cell nuclei. For cells irradiated with gamma-radiation (1 and 2 Gy), an apparent cell survival above unity was observed up to 50 hours post-irradiation, indicating a possible radiation hormesis effect.


CONCLUSIONS
The RBE of 211At found in this growth-assay study was significantly higher than previously presented values. The difference might be due to the use of low-dose-rate gamma-radiation as reference. The RBE presented here could prove valuable when evaluating 211At-labelled compounds for radiotherapy.
Department of Radiation Physics, Göteborg University, Sahlgrenska University Hospital, Sweden. stig.palm@radfys.gu.se
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Palm
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Bäck
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Claesson
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Delle
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Hultborn
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Jacobsson
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Köpf
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Lindegren
D000512:Alpha Particles; D001246:Astatine; D002455:Cell Division / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects*; D003110:Colonic Neoplasms; D005720:Gamma Rays; D006801:Humans; D019047:Phantoms, Imaging; D019904:Polymethyl Methacrylate; D013997:Time Factors; D014407:Tumor Cells, Cultured
D019904:Polymethyl Methacrylate; D001246:Astatine