Spatial dependence of dose rates: An intercomparison between several radionuclides. 1 MBq each of 32P, 67Cu, 90Y, 111Ag, 131I, l88Re, and 193mPt is assumed to be uniformly distributed in a small tumor (radius, 0.05 cm). Note that the high-energy β emitters (32P and 90Y) are not as effective as the radionuclides with medium- and low-energy particulate emissions.