DAMAGE TO THE REPRODUCTIVE CAPACITY OF 

 HUMAN CELLS IN TISSUE CULTURE BY IONIZING 

 RADIATIONS OF DIFFERENT LINEAR ENERGY 



TRANSFER 



G. W. BARENDSEN 



RadiobioJogiad Institute oj the Organization for Health Research TNO, 

 Rijsu'ijk {Z.H.), The Netherlands 



SUMMARY 



Kidney cells of human origin, cultured by the technique developed by Puck 

 et at., (1956) were irradiated with a, j8, 200 kV X- and 20 kV X-radiation. The 

 cells were cultured in special dishes with a Melinex bottom G/j. thick, which per- 

 mitted irradiation from outside with alj^ha particles from ^lopo and beta particles 

 from SOY. The number of cells, which after irradiation had retained the capacity 

 for clone formation, was counted. The survival curve was found to be expo- 

 nential in the case of a-irradiation, whereas with other radiations a more compli- 

 cated curve was obtained, which cannot be interpreted by a two hit mechanism. 



The RBE of a-radiation was found to range from 2-5 at high doses to 6-0 at 

 low doses. From the experiments with a-radiation the sensitive area of these 

 cells for the inhibition of clone formation was calculated to be 40fi^, which was 

 found to be approximately eciual to the cross -sectional area of the nuclei. It may 

 be inferred that clone formation is inhibited if one a-particle passes somewhere 

 through the nucleus. 



Experiments with fractionated doses showed that partial repair takes p\ace 

 after X- and /3-irradiation, but no recovery could be detected after a-irradiation. 



Furthermore cells were irradiated with various doses of a-radiation followed 

 by X-irradiation and conversely. In these experiments no de^Darture from addi- 

 tivity was observed i.e. X-radiation acts on cells surviving after a-irradiation as 

 if they were not irradiated at all. This contrasts with the effect of a second dose 

 of X-radiation, which depends on the amount of X-radiation the cells have re- 

 ceived before i.e. in this case there is some cumulative effect. 



Finally experiments are discussed on the sensitivity of these cells to a- and 

 X-radiation when in eciuilibrium with different mixtvires of nitrogen and oxygen. 

 The absence of oxygen protects the cells in X-irradiation experiments but a very 

 small decrease in sensitivity is found with a-radiation. 



INTRODUCTION 



The development by Puck et al. (1956) of a plating technique for 

 single mammalian cells, whereby each cell grows into a separate clone 

 of macroscopic size has stimulated a number of investigations on pro- 

 cesses which inhibit this unlimited proliferation. The first experiments 



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