Radiotoxicity of Intranuclear Tritium, 125 Iodine and 131 Iodine

L1210 leukemia cells were labeled with various doses of ¹²⁵ I-iododeoxyuridine, ¹³¹ I-iododeoxyuridine, or3 H-thymidine and inoculated into new, nonradioactive hosts to facilitate a quantitative evaluation of the toxic effects resulting from the intranuclear decay of the three radioisotopes. Based on radioisotope incorporation data, peritoneal tumor cell count, labeling fraction, and nuclear diameter of L1210 cells, the rate of intranuclear energy deposition was calculated from the known decay properties of each isotope. Intracellular tritium and131 I produce almost identical effects. The two radioisotopes, both beta emitters, yield survival curves which are characteristic of low LET radiations. Despite their very disparate decay energies, the similarity in tritium and131 I radiotoxicity can be explained on the basis of electron energies deposited within the nuclei of labeled cells. In terms of energy absorption per cell, the toxic manifestations from125 I exceed the e...