Qualitatively different induction of germ cell mutations by heavy ions. A dual target theory.

The problem of the dependence of the biological efficiency of ionizing radiation on the Linear Energy Transfer (LET) is still unsolved. Unexpected reactions of heavy ion irradiated cellular systems such as an increasing Relative Biological Effectiveness (RBE) up to a LET of about 100 keV/micron and then a decrease below 1 oblige to dismiss some conventional interpretations. Several years ago we suggested that, especially by higher ionization density in addition to the DNA, repair systems and (or) membraneous systems could also be injured (dual target theory). Our experiments with heavy ions at the Lawrence Berkeley Laboratory with LET's between 102-970 keV/micron on different types of mutations show a strict distinction between events connected with fusion modalities (repair or misrepair) and those associated with nonfusion. With very high LET misrepair reactions such as translocations disappear, suggesting the direct damage of the repair systems and confirming our previous experiments with peak pions and ions of LET's between 1100-4800 keV/micron.