Nuclear‐Powered Pacemakers

The calculations of the radiation dose to tissue from implanted nuclear-powered pacemakers appearing in the current issue serve to direct attention to a potentially important consideration. In this work it is suggested that since the tissue dose averaged over irradiated organs is well within customary limits, nuclear pacemakers represent an acceptable radiation risk. While the conclusion may indeed turn out to be correct, it is generally agreed that in order for an averaging approach to be applicable, the neutron radiation field should be homogeneous to within approximately 10 /̂-.' The radiation field in the vicinity of a nuclear-powered pacemaker does not satisfy the homogeneity requirement. This can be seen from the accompanying Figures 1 and 2 which have been prepared by simply substituting the near field dose rate of Figure 1 of Jacobson's paper in Figure 2b of that same article. Tbe radiation dose rate to tissue in contact with tbe pacemaker is then ^ 1000% larger than the radiation dose rate only a few centimeters away. In absolute terms, tissue in contact with the pacemaker [particularly the tissue nearest to the plutonium source) is subject to an initial dose rate of ^ 100 rem/year. Over the first twenty years the neutron dose rate will be relatively stable and the total gam-