The dosimetry of bone irradiated by fast neutrons

Bone dosimetry is briefly reviewed and a dosimetric theory applied for the response of detectors to fast neutrons. The detector or cavity shape is characterised by distributions of chord lengths along which the neutron-produced charged particles travel and deposit energy. Cavities of different convex geometries can be treated. Absorbed doses to individual marrow cavities in trabecular bone are calculated over a large range of marrow cavity size for monoenergetic neutrons ranging from 0.5 to 7.0 MeV and for 252Cf neutrons. The influence of cavity shape is explored by considering spheres and cylinders of different elongation. The difference in absorbed dose is not great. A simplified model using a single mean chord length gives results in close agreement. The mean marrow dose to different human bones has been calculated, by using measured chord length distributions for marrow cavities in the bones, by using a sphere with the same mean chord length as the measured distribution, and by applying the measured single mean chord length. Differences between the three approaches are small and agreement good with results obtained by other workers using the Monte Carlo technique. The dose to the endosteal cell layer has also been calculated by approximating the layer with an infinite slab. (UK)