Revision of quality factors in radiation protection

Following an historical overview of the developments in radiation protection and its physical and biologcial bases, the paper deals with the current state in matters of the reference quantities in radiation protection. Radiation-biological results which - notwithstanding considerable uncertainties - seem to indicate a higher relative biological effect of densely ionizing radiation in case of small doses than the quality factors currently in use would lead one to expect, gave rise to thoughts about a revision of those quality factors, for dose equivalents of sparsely ionizing and densely ionizing radiation are not equivalent under the valid convention. From the interim proposals of NCRP and ICRP, discussions arose about the consistency of a solution that is based on quality factors as a function of linear energy transfer (LET) but makes schematic use of a correction factor (2) for neutrons. Theoretical arguments have so far prevented these proposals from becoming a part of the radiation protection regulations. Modifications of the present recommendations may yet come from a further proposals for the revision of said factors by a study group of ICRP and ICRU, and moreover from comparative studies of LET and microdosimetric parameters as well as relevant radiobiological investigations. (TRV)