412 INFLUENCE OF EXPOSURE FACTORS 



If the abdomen only is exposed, the mid-lethal dosage, expressed in roentgens 

 measured in air, is approximately 1100 r, about 400 r above the total-body LD50 

 dose. The clinical effects are very similar to those found after total-body irradi- 

 ation, and it is of interest to note that it is possible to produce this syndrome and 

 death in this manner with considerably fewer gram roentgens than are required 

 nith total-body irradiation. 



If the abdomen is shielded, however, and the remainder of the body is ir- 

 radiated, the mid-lethal dose is about 2000 r, and the animals die with chnical 

 signs quite different from those seen after total-body irradiation. If only the 

 head is exposed and the remainder of the body is shielded, death occurs at ap- 

 proximately the same dose level with weight loss compatible with that seen in 

 starvation. 



It was of interest to see whether the syndrome of acute total-body radiation 

 illness could be approximated by means of irradiation confined to small portions 

 of the abdomen. If one half of the abdomen was exposed, the dose necessary to 

 kill was about 1600 r and the clinical picture was not greatly different from that 

 of total-body irradiation. 



To obtain highly selective irradiation, we were fortunate in having access to 

 the 190-mev deuteron beam produced by the 184-in. cyclotron in Berkeley. The 

 beam traverses the entire width of a rat with essentially no lateral scatter, and 

 the RBE of the ray, as determined by total-body lethality studies in mice, is 

 approximately 1. A ^^-in.-diameter beam was used, which will irradiate ap- 

 proximately 12-14 grams of tissue as it passes laterally through a rat. 



It was found that irradiation confined in this manner to the abdomen produced 

 acute deaths at dosages of the order of 2000 rep, and the cUnical picture showed 

 definite variations from that seen after total-body irradiation. In addition, no 

 particulary "sensitive" region was found; irradiation of large portions of the 

 liver, spleen, or stomach at comparable doses did not produce a syndrome 

 analogous to that following total-body irradiation. 



Lateral irradiation to include both adrenals (plus a portion of the spine) pro- 

 duced no visible acute effects at 3500 rep; however, some of the animals devel- 

 oped paralysis of the hind Umbs about 2 months after irradiation. It is of in- 

 terest also that, while locaUzed gut irradiation produced adrenal hypertrophy 

 and thymic atrophy, depression of the red-cell elements of the bone marrow did 

 not occur. Depression of the red-cell elements can be demonstrated 24 hr after 

 total-body irradiation by observation of the rate of uptake of radioactive iron. 



Hahn: 



It may be pertinent at this time to point out that the pathological human 

 organism may be used as a test tube in the study of irradiation effects on cells. 

 As Tobias mentioned yesterday, there are often relatively simple relationships 

 existing, as for instance in the equation he gave for cell sur^^val, N = NqC ^^. 



In the treatment of chronic leukemia in human beings by intravenous admin- 

 istration of single doses of colloidal metaUic gold^^^ the isotope is deposited in the 

 reticulo-endothelial system, largely in the liver. The resultant drop in white- 



