t Ur 113 _iryboski, J. D. and Gotoff, 8. P. Vew Eng. J. Med. 265, 1829 (1961). + »; Schroeder, H. A., Balassa, J. J., and Vinton, W. H. J. Vuir. 86, 51 (1965). stover, B. J., Atherton, D. R., Buster, D. S., and Keller, ie of N. Radiat. Res. 26, 226 (1965). Po. Wallaee, D. E., Stehney, A. F., and IJcewicz, F. H. Argonne National Laboratory Radiological Physics Division. semiannual Report January—June 1957. ANL-5755, p. 33. Roo crrillmaier, R. Biophysikalische Untersuchungen an Personen mit Ablagerungen von Radionukliden der natirlichen Thoriumreihe. Ph.D. Thesis, Homburg/ Saar, 1964. Box Parr, R. M. Ann. N. Y. Acad. Scr. 145(3), 644 (1966). fog Bohr, N. Agl. Danske Videnskab. Selskab, Mat.-fys. Medd. 18(8) (1948). Ee Nielson, K. O. Electromagnetically Enriched Isotopes and Mass Spectrometry, Ed. M. L. Smith. Butterworths, London, 1956, pp. 68-81. B31. Marinelli, L. D. Private communication. . P23 Bensted, J. P. M. and Crookall, J. O. Bret. J. Cancer 17(1), 2 (1963). Feo’ tlursh, J. B. Misbehavior of thorium daughters formed in Thorotrast. Paper presented at the Ist International Congress of the International Radiation Protection Association, Rome, Italy, 5-10 September, 1966. ¥o3t. lWursh, J. B. Personal communication quoted in Reference 11. “oy Baserga, R., Yokoo, H., and Henegar, G. C. Cancer 18, 1021 (1960). fe... (irilimaier, R., Muth, H., and Oberhausen, E. IAEA symposium on Assessment of Radioactivity in Man, Proce. IAEA Symp., Heidelberg. Int. Atomic Energy Agency, Vienna, 1964, Vol. 2, p. 473. 37. Stover, B. J. Proc. Soc. Exptl. Biol. Med. 100, 269 (1959). 7 38. Marinelli, L. D. IAEA-WHO Panel Meeting on Dosimetry and Toxicity of Thorotrast, Vienna, October 1965. Int. Atomic Energy Agency, Vienna, 1968, Tech. Report 106, p. 86. on Dudley, R.A. Ann. N. ¥. Acad. Sez. 145, 595 (1966). F 40, Muth, H. and Grillmaier, R. IAEA-WHO Panel Meeting on Dosimetry and Toxicity of Thorotrast, Vienna, October, 1965. Int. Atomic Energy Agency, Vienna, 1968, tope. In general, it is necessary to distinguish three types of atom; those which enter the circulation in the injection materials (tvpe I), those which grow77vivo as daughters of injected atoms (type II), and those which grow in vivo as granddaughters of the injected atoms {type III). (In the present context, since we are dealing with growth and decay on a time scale long compared to the half-life of Ac, the decay chain ?°Th:*%Ra:°%Th is visualized as a_ parent:daughter: granddaughter series). At the time of injection, therefore, all the 2Th, “Ra, and “*Th atoms are of type I. At anylater time, ?%Th atoms are of types I, IT, and III, *8Ra atoms are of types I and II, and all the °®Th atoms remain of type I. For a Thorotrast body burden of very long standing (sufficiently long for essentially all the 8Ra atoms of type I to have decayed away), we can write the follow- ing for the activities in any tissue sample and in the whole body. (See Table 53.) TABLE 53. ActTiviTtes FoR 4 LONG-STANDING THOROTRAST Bopy BurpEN 22Th (type I) Tissue sample activity Whole body activity Tissue/whole body ad» Ag a ! 28Ra (type IT) 228Th (type ITI) Filado] fidg afs/fi frlfiaAo] felfidol afifo/fife Aa is the activity of ™?Th in the whole body (equally the activity of “2Th in the total injection material) and a is the fraction of this administered material contained within the tissue sample. These expressions define the quantities f; and f: for the tissue sample, and f, and f2 for the whole body, as F 41. Rotblat, J. and Ward, G. B. Nature 172, 769 (1953). the steady state activity ratios which it is desired to calculate. It follows that, of all the ?®Ra atoms born within the entire body which have not undergone decay F APPENDIX within the body; and amongst the different tissues these Tech. Report 106, p. 79. Calculation of the Steady State Activity Ratios ( SRA/27H) and (Th/*™Ra) in vivo ‘. rigorous mathematical treatment of the #*Ra and ““Th activities 2 vivo is complicated by the fact that Thorotrast is a nonhomogeneous material in which the + radioactivity is probably distributed throughoutseveral different. physical phases in proportions whichare differcnt for each nuclide. For this reason alone, and without tesird to differences in physical half-life, it cannot be ‘issumed that different isotopes of the same element will ‘ow the same pattern of tissue distribution in vivo F (. ™8Th and 2®Th, or 2*Ra and 2%Ra). Moreover, a thorough analysis of the problem even demands that f ‘“ctinetions be drawn between atoms of the same iso- by the time of sampling, a fraction f; remains then retained atoms are distributed in the proportions afi//t . Similarly for “®Th, f, measures the fraction retained in the whole body, and afif2/fif2 measures the distribution of the retained atoms amongthedifferent tissues. This discussion refers to a Thorotrast burden of such long standing that none of the type I **Ra atoms and none of the types I and II ?8Th atoms survive. At earlier times it is obviously necessary to consider the fates of theRa andTh atoms contained within the administered Thorotrast. For #*Ra it will be assumed that all type I atoms distribute themselves in the same proportions af,/f, among the different tissues as do the type II 28Ra atomsreferred to in Table 53 and that the whole-body retention is f,. Similarly, the 28Th atoms of type IT will be assumed to distribute themselves in the pb ay