Dose delivered to various bone and marrow sites of radium 226 injected mice related to the observed heterogeneity in damage to haemopoietic marrow cells

A method of determining local radiation doses from ²²⁶Ra to selected bone marrow sites of ²²⁶Ra-injected mice is presented. The ²²⁶Ra burden in selected cortical and trabecular bone sites of BALB/c mice and the morphometric characteristics of these bone sites and of their marrow cavities in BALB/c mice are measured. These data, along with information on dosimetry from the literature, are used to calculate the cumulative dose in the selected bone and marrow cavity sites. The amount of ²²⁶Ra picked up by a bone is shown to be linearly related to the area of bone surface. The energy absorption in various bone and bone marrow sites is not homogeneous. The relationship between local marrow doses and the observed non-uniformity in damage to haemopoietic marrow cells of different marrow sites 300 days after ²²⁶Ra injection is discussed. The degree of marrow damage does not simply reflect the calculated marrow dose. This dose-effect study gives some indications for (1) a modification of the approach used in local ²²⁶Ra dosimetry and (2) additional damage to the stem cells due to irradiation of their regulating system.