Article: Pathology of Irradiation, Edited by C C Berdjis (Plutonium Injection Experiment)

Page 2

The Williams & Wilkins Company All rights reserved. This book is protected by copyright. No part of this book may be reproduced in any form or by any means, including photocopying, or utilized by any informat ion storage and retrieval system without written permission from the copyright (0 LbLibrary of Conps Catalog Card Number 71-110278 Composed and printed at the Waverly Press, Inc. Mt. Royal and Guilford Aves. NATIONAL LIBRARY OF MEDICINE

Page 3

Some Toxicity Aspects of Internally Plutonium-239 is a good example of a radionuclide which is retained within the body for prolonged periods, and thus irradiates selected organs or specific tissues within an organ with relatively high energy (5.14 mev) alpha particles.’.’” The range of a 23yPu5.14-mev alpha particle is approximately 35 p in soft tissue and behavior also typifies the complex problems encountered in the study of internal radiation. For example, the deposition pattern is markedly influenced by the route of entry into the body, the physical and chemical states of the radionuclide before and after exposure, the age and metabolic state of the organism a t the time of exposure, and species differences -just to mention a few of the variables. Further complexities arise from the ever-changing tissue concentration and unequal distribution patterns of the radionuclide within a given tissue or organ. Also, the specific target cell is frequently unknown. Thus, the precise local dose for a given response is seldom known. In some instances the dosimetry is further complicated by the continuous movement of cells into or away from the radiation field. Also, precise latent periods for the various lesions are usually difficult or impossible to determine, since the lesion is usually not detected until sometime after the injurious dose was received. Thus, the induction dose is usually significantly less than the accumulated dose a t the recognition time of the lesion. These factors are just a few of the variables involved in evaluating the effects of internally deposited radionuclides on the components of a dynamic biologic system and suffice to emphasize some of the problems encountered and the potential variability in the toxicity syndromes induced by the respective radionuclides or various physical and chemical states of the same radionuclide. Thus, the toxicity syndrome of pJyPuin a dog, as presented in this study, is not given as a typical example of internal radiation but as a specific case indicating some of the major end-points induced by one of the more important and very toxic radionuclides. Nevertheless, it does serve to indicate some of the more general factors involved in the study of internal radiation. All of the animals summarized in this study were pure-bred beagles which were progeny from a moderately inbred colease-free conditions, and environmental, dietary, and general animal care factors were comparable for each animal throughout its life span. The pJutonium was administered in the tetravalent form, in a citric acid sodium citrate buffer (pH 3.5) via a single intravenous injection, at approximately 16 to 17 months of age.” All of the epiphyses were closed a t this time, except those of the costochondral junction. The animals were kept until death or were sacrificed when death was imminent. The dose levels and numbers of dogs observed are shown in Table 7.1. The percentage fractures (shown below in Fig. 7.6) were based on the total number occurring in a specific bone, as related to the total number of these bones pres-

Page 4

some of the ical states of of the major of the more arized in this iistered in the xcept those of one, as related ent in the given number of dogs a t the respective dose levels. The fractures shown for the thoracic vertebrae were limited entirely to the dorsal spiKous processes and those for the lumbar vertebrae involved both dorsal spinous and The induction times for the osteosarcomas are the intervals from injection of 23yPuto the time of death and not the time of first recognition. The autoradiograms are from acetonefixed tissues, prepared according to the method of Arnold and Jee.I3 Following a single intravenous injection of tetravalent p''yF'u,most of the retained radionuclide burden was ultimately localized in the skeleton (approximately Sori) and the liver (approximately 30C;), where it was retained for prolonged tion sites were the thyroid," the kidney, and the spleen.'.' Thus, these and the immediately adjacent tissues, such as the bone marrow, were the principal target organs. The following observations summarize the most significant aspects of the The earliest clinically detectable radiation-induced change was a drop in the leukocytes of the peripheral blood." The depression was most acute at the 2.8 p C per kg dose and became minimal or nonsignificant below 0.095 p C per kg. Partial recovery occurred a t various postinjection times, which varied accord in g to the injected dose level. In spite of the very significant blood dyscrasia, death due to hematopoietic changes did not occur and hematopoietic neoplasms were Approximately 25';; of the dogs injected a t the highest level died with primary ning at approximately 400 days postinjection, In the cases of primary liver disease, the liver a t death was one-half to ondary portal hypertension was invariably present. The earliest evidence of hepatic injury was a significant elevation in the serum glutamic pyruvic transaminase which occurred approximately 200 days hepatic syndrome indicated that the 3 very near the LDso for the dog, with death due to subacute primary liver disease at post-injection times greater than 400 days. Significantly higher doses would FIG.7.1. Autoradiogram of 6 - p section of beagle liver taken 13 days followinp; a single intravenous inform distribution of alpha tracks (arrow) arising from the hepatic epithelium. Exposure. 27 days. X380.

Page 5

PATHOLOGY OF IRRADIATION undoubtedly lead to more acute deaths from hematopoietic factors. Initially, the 'j9h was uniformly distributed throughout the hepatic cells and was strikingly absent from the reticucluding the biliary epithelium (Fig. 7.1). This pattern persisted until approximately 200 to 300 days post-injection, after which a significant translocation of the 2JyAIto the RE cells produced promia high percentage of the radionuclide was localized in the individual RE cells lining the sinusoids, especially at the highest dose levels. The formation of the first hot spots coincided with the earliest rise in SGPT and was probably the result of increased liver necrosis. The rate of movement into the RE cells appeared to be a function of the degree of injury to FIG. 7.3. Autoradiogram of 6 - p section of beagle her taken 1.400 days following a single intravenous gregation of a high percentage of the plutonium in the portal areas, which occurs at relatively long postinjection times. Exposure. 27 days. X38O. FIG. 7.2. AutoradioPam of 6 - p section of beagle liver taken 362 days following a single intravenous injection of 0.303 p C of '.IYPu per kg which shows the early translocation of the radionuclide t o the RE cells (arrow). Also shown are foci of relatively nonradioactive parenchymal cells (N). Exposure. 4 7 the hepatic parenchyma and was greatest a t the highest dose levels. A distinctive feature in the translocation of '"AI to the RE cells was its assosumably hemosiderin. The ' 'Pu in liver cells other than the hepatic epithelium was seldom observed in the absence of such iron-shining material and appeared to be bound to this compound. Following the shift of '"hand the associated iron pigment to the RE cells, a further translocation to the stromal areas, including the subcapsular regions, occurred until ultimately a high percentage of the '"h retained in the liver was localized in these areas (Figs. 7.3 and 7.4). This feature was most obvious and occurred a t shorter post-injection times a t the highest levels. Again, the alpha activity was invariably associated with iron-staining pigment and a high percentage was still retained within

Page 6

ection of beagle le plutonium in Pu in liver ilized in these is feature was macrophages, which presumably served as transport vehicles from the more central areas. This movement to the stromal areas was obviously quite efficient, since the plutonium was lost from the liver at The plutonium distribution pattern was also influenced by regenerative changes. This was principally a mechanical displacement of the older radioactive tissue by foci of younger regenerating hepatic cells of very low plutonium activity (Fig. 7.5). These changes were prominent even a t the lowest dose level, 0.015 p C per kg, but only after relatively long latent periods. Such regenerative changes represented a replacement phenomenon since the liver weight usually remained normal even though 70 to 80'; of the liver was eventually composed of regenerative FIG. 7.4. Autoradiogram of 6 s section of liver showing the late localization of plutonium in the subcapsular areas. Same dog as Figure 7.3. Exposure. FIG.7.5. Microphotograph showing numerous foci of regenerating hepatic cells (R)in a beagle liver 3,430 days following a single intravenous injection ' Includes only dogs 8 years or older. tissue. In spite of the very marked liver changes, fibrosis did not occur. A third factor in the plutonium-induced liver syndrome was a moderate number of primary liver tumors which occurred in the long-term low level animals. Table 7.2 summarizes the incidence observed All of the tumors were the bile duct type. Only two were the primary cause of death with the others being quite small and found incidentally a t autopsy. Another feature of plutonium toxicity was the induction of pathologic fractures. These occurred in the three highest dose levels: 2.8, 1, and 0.3 p C per kg (Fig. 7.6). The earliest fracture was observed approximately 390 days post-injection, with an average skeletal dose of 3,180 rads." The incidence dropped sharply between 2.8 and 1.0 pC per kg doses and became

Page 7

FIG. 7.6. Anatomical distribution and percent incidence of pathologic fractures ip dogs following a single intravenous injection of 'Vu. insignificant a t the 0.3 p C per kg dose level. A significant percentage healed normally when they were properly imIn spite of other very obvious radiographically apparent changes, the fracture sites usually could not be predicted by radiography. This was in agreement with strength tests of defleshed bones which established that '"'Pwinduced changes in the breaking stress were not sufficient to account for the pathologic fractures and the etiology was tentatively ascribed to the induction of localized bone A unique feature of these radiationinduced fractures was the minimal amount of pain associated with them. An abnormal rate of tooth loss was first observed a t the 0.0948 pC per kg dose level and the rate increased with each successively higher dose (Fig. 7.7). The dental lesions, which ultimately resulted in tooth loss, were clearly separable from the naturally occurring nonradiation fac tors such as the periodontal syndrome and were similar to those induced by other bone-seeking radionuclides, such as radium and radiothorium. The lesions, as seen radiographically, were characterized by loss of the periodontal ligament, ankylosis of the roots, unique dental caries, and exfoliation of the crowns in the advanced cases (Figs. 7.8 and 7.9). Varying degrees of root resorption occurred prior to, but especially after, the loss of the crowns. Marked lesions in the adjacent bony structures occurred concurrently with the tooth changes. Radiographically these were seen as coarsening and loss of spongy bone and formation of radiolucent foci in the mandibular cortex, especially a t the higher dose levels. Dental radiography was the most sensitive in vivo method of detecting nosneoplastic plw toniuminduced skeletal injury. Within general limits it was possible to determine the dose level by examination of the dental occlusal films. In addition to the fractures and bone tumors, an additional very obvious plunate osteolysis (Figs. 7.10 and 7.11). This was marked a t the higher dose levels and occurred to a lesser degree down to levels as low as 0.5 p C per kg. In the lower doses it was frequently the only non-neoINJECTED pC11b.g OF BODY WEIGHT FIG.7.7. Comparison of the regression coefficients for rate of tooth loss in beagles injected with 'JyPu.

Page 8

iental caries, and in the advanced ed prior to, but t of the crowns. ening and loss of on of radiolucent ible to determine mination of the actures and bone er dose levels and ree down to levels kg. In the lower lk9 OF BODY WEIGHT les injected with ""h. plastic skeletal lesion that was obvious during the gross postmortem dissection. Thus far, primary neoplasms have not occurred a t this site and the osteolysis did not produce serious clinical problems. The apparent atrophy resulted from varying degrees of osteolysis involving the thin, bony laminae which formed the framework of this structure. In some of the highest levels, complete loss of the bone occurred. Changes in the overlying mucous membrane were not remarkable. FIG. 7.10. (Top.) Photograph of midsaggital section through beagle skull with nasal septum removed showing the normal appearance of the madlo - FIG. 7.11. (Bottom.) Photograph of midsaggital section through beagle skull 1,400 days following involution of the marilloturbinate and ethmoturbiFIG. 7.8. (Top.) Radiograph of left mandible of 692-day-old beagle showing normal bone and dental FIG. 7.9. (Bottom.) RadioFaph of left mandible of beagle 1,338 days following a single intravenous injection of 0.838 UC of ''"Pu per kg showing dental cariea, root resorption, loss of the periodontal ligament, and marked coarsening of the sponRy bone of the alveolar crests. Same dog as Figure 7.8. X2%. Similar lesions were seen in the ethmoid labyrinth but were less obvious grossly. The identical syndrome also occurred in dogs treated with other bone-seeking Th. It was not observed in animals treated with relatively high doses of betaThe leading cause of death following intravenous injection of tetravalent vJyPu was the induction of osteosarcomas.PU.2' Thus far such tumors have occurred as low as the 0.0158 p C per kg dose level

Page 9

116 PATHOLOGY OF IRRADIATION and a t an average cumulative skeletal dose as low as 60 rads. Since the cumulative rad dose was based on the survival time, the tumor-induction dose was less than this. However, the local dose to the critical cells, because of the surface deposition, was much higher than the average skeletal dose. The average length of time from injection until death from osteosarcoma generally increased as the dose was lowered; however, the range of the survival times for some of the injected dose levels overlapped significantly (Fig. 7.12). The anatomical distribution of such neoplasms was more generalized than described for the nonradiation-induced bone tumors observed in other canine The spontaneous osteosarcoma incidence in the beagle is very low and lies somewhere between 1 to 100 cases per 100,OOO deaths." Thus it is fairly certain that all the tumors presented in this study were In general the plutonium lesions were localized within the focally irradiated areas. However, several conditions developed which may have been secondary to the overall radiation effect. Some of these, especially the decreased longevity FIG. 7.12. Average osteosarcoma latent period of beagles receiving a single intravenous injection of Pu. The range of the latent period is desimated by the vertical bars and the percent incidence is shown …