hanes C1 sae tated da ae2 alle Bs edt talioe, 98 0 (parent) | 1 | 2 227h 28Ra 228A¢ 2287 h Half-life ; | | LAX 10M y 5.75 y 6.13 h L.Oly 0.14 us 3.1m an 22P 6 208T |] 0.34; 0.97; others up 33 (0.17) 67 77 36 6.05 2.20 8.78 1.77 wa 9 10 55 42 (0.83) Oo 60.5 m QC 21273) 10.6 h WHA 8 212Ph 10 053 6.26 0.3387) 0.663) = 3.62 d 54.58 0.165 WR *4Ra 220Fim 216Po 7 ; R 4 5 6 Principal gamma-ra: a energies Particle emitted and energy, MeV ca 3 Nuclide Oe | tre Serial number of decay product Decay PARAMETERS OF THE Th Decay SpERrES Q TABLE 34. 0.241 (weak) — —_ 0.239 0.73 (weak) — 0.58; 2.62; and othe ‘* Only gamma rays greater than 0.10 MeVin energy and more than 1% abundant arelisted. determination of radiation dose. However, dosimetry in these cases is a problem of great complexity since energy is deposited within the tissues not only by the parent nuclide, *8°Th, but also by a long series of radioactive descendants (Table 34), each of which is translocated according to its own peculiar metabolic characteristics. Other problems also serve to complicate the dosimetry, such as the very nonuniform distribution of the colloid in the bodyand in anyone organ, as well as the self-absorption of the radiation within aggregates of Thorotrast particles. The general metabolic patterns of behavior of the longer lived nuclides *°Th, 2°8Ra, 2°8Th and 774Ra can be described in broad outline from the work of Rundo,‘**#) Rotblat,“?) Kaul-®) and their coworkers in Europe, and of Hursh‘*-!) and Marinelli@? ) and their collaborators in the United States. To a lesser extent, data are also available on the metabolism of the shorter-lived daughter products 72°Em,‘!%15, 14) 212Pb, and “!*Bi.: ©) However, much of this knowledge is based on a very small numberof tissue measurements, which particularly for the shorter-lived daughter products, is very scantyindeed. The present program of investigation was undertaken with the aims of (1) checking the validity of some of the currently accepted data on Thorotrast MATERIALS AND METHODS Sources of Tissue Samples Analyzed The attainment of the main objectives of th vestigation required a study of tissue samples typical Thorotrast patients, most of whom re: injections of the material 20 to 30 years previ To this end, various smal] autopsy samples we: tained for analysis through the kind cooperat several physicians who had an interest in the 1 trast problem, However, it proved extremely di to gain access to more than a very small num! such specimens at a sufficiently early time after for the study of the shorter-lived daughter pro. For this reason—but also to obtain data on the metabolism of Thorotrast—the investigation of term Thorotrast patients was supplemented ir ways. Firstly, short-term studies were conduct: terminal cancer patients injected intravenously th a catheter with known amounts of Thorotras: lected tissue samples were examined promptly death. Secondly, a series of animal experiment: performed using rats and dogs injected intraven and then sacrificed after intervals up to about 2 from the time of injection for prompt examinati the tissues. These animal experiments were i1mp< metabolism and (2) studying particularly the metabolism of the shorter-lived thorium daughter products, “28Ac, 74Ra, 772Pb, and *4*Bi. On the basis of this for the understanding they afforded of the behav the short-lived nuclides, ?88Ac, 777Pb, and 71°Bi. ing of the factors on which the dosimetry of Thorotrast determination of the 73*Bi activities. knowledge it was hoped to obtain a better understand- depends. This report also seeks to summarize the more important measurements of other workers in this field, and hence to derive the current “best estimates” of the radiation dose delivered to the tissues of Thorotrast patients. in such cases could the measurements be comm at sufficiently early times after death (<1 hr) to Radwactivity Measurements Small samples of tissue weighing up to abou were used for the radioactivity determinations. growth and decay of 7*8Ac, 7?°Pb, and 7°°T1 wer