syhdibendtaders Salad Atak Se a tent ge 1 bea sane vaelsals edataat eietetiongd wy va, vaMener Tne Se Be Ly a atmta NRESaco tet Tiber Rh tek CnZe me apa totems ee TOAVICOLOGY OT RADTIOIECEINES . Since the units for dose ofexternal radiation “at try to present doses associated with the me “reflects the deliberauions, if not the methods, of caiculaung absorbed dose ” (125, p. 108} of NERD cut on the whole provides a somewhat more chassn | Foirsat. Also. e geod sarees of the “classical” appioacn ca oe found he tis venris (.e., Tdas and reins). Since the absorbes chapier by Harper (13>. andthe book oy Hendee (133). . sees of absorption, distribution, retentions spanization from orcan systems te wos bo the toxicology of radionuclides is dev oted wioucoxinctics. Space prevems aay serions wture here, Also in the practice ef nuciear wtien reasonable limits the radiation dose to te prevent undue exposure in diagnostic sherany. ss compttation devised large: by Marinelli, siaany applied since the iate i9sus, has been uty (E25), Rather elaborate ecguations have Ie, point sources, surface and volumesources, ‘126) a simpler, more genera! treatment was -tce of nuclear medicine. To accomplish this a -atttna! Radiation Dose Committee’ (MIRD) Hundreds of narers have addresssd dorimetriz problem. of a particula isotope in a particular ss sien. These cannot be reviewed here except in connection with dose-response relat ionships as a general probiem. OFspecial intcrest, however, is @ odvies cv parters from the New York University fasutute of Environmental Medicine by Wrenn and colleagees (134-136), on the radiation cose from nuclides that ceeay by electron capture or internal conversion. It is pointed out that frequently Auger electron emissior, which can occur in such cases, 1s “more probable thar +-ray emission for elements of biolog:cal interest” (134, p. ij. The range of ar Auger eiectron is consider: biy Shortes nan the mean iree rath of the equivalent \-ray. Therefore conventional dosage catculations my be quite inaccurate if the biclogical object of importance is srnal] compared to the mean free path of the anticipated x-ray. If specific localization of an Aurer electron emitter occurs in sub-cellular structures, very localized irradiation may take place. Conventional dosimetric calculations assuming uniform distrioution ‘¢ the Journal of Nuclear Medicine (127-130) -rmutiee and its sponsors. They present as a ” ‘tnevific absorbed fraction” (= d/m where ..8 mm} which had been introduced earlier for Wrenn (134) showed that the difference in dose to the erythrocyte with Fe-55 is a factor of 10 higher than to the rest of blood because of these phenomena. and with some iron-containing complexes such as ferritin which bind closely to intra-cellular structures. the difference between local dose and a conventionally 2 vaiiphlets give the schema, tables of absorbed calculated one may ve even greater. Feige et al (137) and Gillespie et al (138) ‘ine MIRD schema is to provide a single Dese-effect retutionships—Understanding and formulating the reiationship of dose to effect is especially important ir, considering the eifects of radionuclides at this time because of the strong current emphasis on the effects of verv low would miss this almost entirely. st Nuclear Medicine. Several pamphlets have have explored the physical dosimetry in thyroid for '?°J, another Auger electron “emitter.” cratsa, and other needed information. Future vabstances of interest in nuclear medicine, set any Source of activity to any target for ail “ate peneral anolicability as long as relevant - ! 1 time (126). This jatter is a not inconsideriat te the eatent that aksorbed fraction doses. Acute effects at high doses of both external radiation and internal emitters generally follow the sigmoid relationship familiar in chemical toxicology. But nicters ofinterest for predicting biological set &' ve Giem directly, the new plan has advan- genetic effects of radiation are characteristically linearly related to dose with no apparent threshold [with a recent exception—female mice (139)} and the same Peatan obvious simplification but it zenesis. This has been termed the “linear no-threshold raodel.” The 1972 parer relationship is postulated to hold for some somatic effects including carcino- ¢ Manne, Quimby & Hine methods, the of Evans, Keane & Shanahan (37) presents a useful history of this corcept as applied to radiaron protection, where it was adopted primarily because it was ‘uitely the absorbed doses calculated by Whe diferent from those caleulated ' conservative (114, 140). That i gives an upper limit to risk is evident to the extent that cpe ¢ ue relationship his teow 4a linear extre polation from do-es for wich duta are extant. ivans et al nave taxen the view that the region of no-effect descr-bec in the SRD committee iy che compilation Jigs admuusiered as lsbelied pbarrea“ssech as chemical er) rad ochemica! secugn Of Carcinogenesis above is tuntamount to a “prayceal thresheta’’ in that the incidence is so low within the life span of the species concerned as to be negligible. Others (141-145) do not accept this view and miainiain in essence wb eeidee Cose. Lo waisted a Lmely and complete chapter on - ‘aad tae researcher and the physician. Ii hh ee al POPeseeengyemeeree Tere rmae, BOREAS“PeepAgraren Naeeee f “he 3 “ap spate det,kp. PNT SEATGop) wee memes tee ttt Ce at em at Wibahdats ttApesveraypeer peers Theyre + Lanep viby e Sha eleigh a hbowe HE Eo apatite hoes hee * , : piste 2 yo Beotghen ’ tag OR va sees . Toye ’ ePeGet ah pee wage i . fbr 8 ~ Por ee xVac HT ae Bae . 2 Fe rr 4. bt ce mene + * . vy eet ene Mr © “ aSsesqateneeakaepeatedgit ep FL ous coon the Spee? ge ode>lite ! La eat Baed in got le thas nes eePea sply Paacehin Hw. Opp TENye RD eet