Developments and trends in bioequivalent dosimetry.

Significant progress in radiobiology has refined the understanding of radiation-induced biological response at the cellular level and challenged the conventional application of a macroscopic description of radiation action to dosimetry in favour of a microscopic approach. Pioneering experiments, which investigated the stochastics of energy deposition from ionising radiations in volumes of cellular dimensions, contributed to the recognition of microdosimetry as a new scientific discipline. The first quantitative applications of Monte Carlo track structure simulations in radiobiology, however, supported evidence for target sizes of particular biological importance being in the nanometre regime. Bioequivalent dosimetry attempts to link particular features of the response of physical detectors with biological endpoints, exploiting clusters of multiple ionisations within nanometre scales in solid-state, gas- and water-filled devices. This approach supports the continued development of new concepts and quantities in radiation protection to permit evaluation of the biological effectiveness of radiations of different quality independently of dose and dose rate.