Biological effects of heavy particles

The usual definitions of biological dose and biological dosimetry do not fit in case of particles with high linear energy transfer (LET). The dose corresponds to an average value which is not representative of the highly localized energy transfer due to heavy ions. Fortunately, up to now, a biological dosimetry following an exposure to high LET particles is necessary only for cosmonauts. In radiotherapy applications, one exactly knows the nature and energy of incident particle beams. The quality requirements for a good biodosimeter include reliable relation between dose and effect, weak sensitivity to individual variations, reliability and stability of acquired informations against the time delay between exposure and measurements. Nothing is better than the human lymphocyte to be used for measurements that fulfil these requirements. In the case of a manned spaceship, the irradiation dose corresponds to a wide range of radiation (protons, neutrons, heavy ions), and making a dosimetry as well as defining it are of current concern. As yet, there exist two possible definitions, which reduce the dose either to a proton or to a neutron equivalent one. However, such an approximation is not a faithful representation of the irradiation effects and in particular, the long-term effects may be quite different. In the future, it is reasonable to expect an evolution towards technics that enable identifying irradiated cells and quantifying precisely their radiation damage in order to reconstruct the spectrum of particles received by a given cosmonaut in a given time. Let us emphasize that the radiation hazards due to a short stay in space are quite minor, but in the case of a travel to Mars, they cannot be neglected