A study, funded by CEC, was set up essentially to study the effects of low X-ray doses using cells from 4 subjects and the results (Lloyd et al, Int. J. Radiat. Biol. 53, 4, 1988) were compatible with a possible threshold at doses less than 20 mGy. This was later extended (still to be published) to blood from a further 20 subjects. Despite large numbers of cells being analyzed the statistical uncertainties on the data were fairly large. Nevertheless a similar conclusion of a threshold could still be drawn. If the low dose response is really linear as has been the usual assumption in radiobiology, it is remarkable that three studies have all shown, albeit each not significantly, evidence for a low dose plateau in response and a reduction below the control value at 10 mGy or less.
The present project forms an extension of this work to obtain data using low doses of high LET radiation. Samples of blood from 4 subjects will be irradiated at the Fast Neutron Facility at the Reactor Centre Petten, The Netherlands. Expertise from NRPB, together with the staff at the Reactor Centre will be used in the dosimetry. Eight doses (0, 0.25 0.5 0.8 1.25 2.5 12.5 and 62.5 mGy) will be used and the incident neutrons have a mean energy of 1.0 MeV. The irradiated samples will be taken to Leiden for culturing for metaphase preparations using a standard protocol. Many replicate slides will be prepared, coded and distributed between the six participating laboratories for microscope analysis. After scoring the data will be decoded and evaluated by statistical programs at NRPB.