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ALPEN, E. L., AND POWERS-RIsIus, P., The Relative Biological Effect of High-Z, HighLET Charged Particles for Spermatogonial Killing. Radiat. Res. 88, 132-143 (1981). The testis weight loss at 28 days after irradiation was used to assess the relative effectiveness of high-energy heavy ions for cell killing of mouse spermatogonia. The testis weights are corrected for the radiation-insensitive fraction. With this model the data were found to fit an exponential survival curve with no shoulder. For all ions the extrapolation number is 1.0. For 60Co radiation the extrapolation number is 1.0 and the Do is 107 rad. All ions have killing effectiveness higher than 60Co radiation except nonstopping helium ions. The radiation modalities used were 228 MeV/amu helium ions and 400 to 670 MeV/amu carbon, neon, and argon ions. The RBE for spermatogonial killing was a maximum of 3.0 for plateau argon ions. Both neon and argon ions were shown to have reduced effectiveness if the LET exceeded 100 keV/Mm. One of the most significant observations made in these studies is that LET alone does not predict the effectiveness of the various ions. Large differences in effectiveness are seen as a function of atomic number of the particle, even though LET is held approximately constant. |
