W. M. COURT BROWN AND JOHN D. ABBATT 



this response from this aspect are reinforced by the obvious inverse relation- 

 ship existing between the length of the latent period and the approximate 

 duration of the acute symptoms {Figure 4) . These relationships appear to 

 hold not only for the cases subjected to medium voltage X-rays but also for 

 those given large doses of ^^^I. In this latter group the whole body dose 

 corrected for renal and thyroid clearance has been calculated according to 

 principles laid down by Mayneord and Sinclair^. In this instance the 

 mean dose rate per hour has been plotted against the latent period. 



No correlation has been found between the length of the latent period 

 and whole body integral dose in either the cases treated with X-rays or 

 with 13^1. This is not surprising as the implication of such a correlation 

 would have been that energy absorbed in all tissues would be equally effective 

 in the production of this syndrome. 



A consideration of the X-ray dose per unit of body size recjuired to pro- 

 duce latent periods of comparable length gives some indication of the 

 radio-sensitivity of differing anatomical sites. Thus it can be shown that to 



6r 



Figure 4. Relationship of the length of the 



latent period to the duration of the period of 



acute symptoms 



{44 cases) 





s 



I' 



Irradiation of whole spine 

 " abdomen 

 upper trunk 

 ^vho/e body 



12 3^567 



Duration of tt)e period of acute symptoms 



8 



produce latent periods of similar duration following irradiation of the pelvis 

 alone or of the whole abdomen, the X-ray dose to the pelvis has to be about 

 five times greater than that to the abdomen. 



The influence of body size and the relationship that exists between the 

 length of the latent period and the period of acute symptoms suggests that 

 the production of symptoms is related to the concentration of some circula- 

 ting compound. On this hypothesis it would be expected that a given X-ray 

 dose would produce a constant amount of this substance, which on passing 

 out of the irradiated volume of tissue would become diluted in some fluid 

 compartment of the body. An interesting piece of indirect evidence in 

 favour of this hypothesis has been noted in some of the patients given large 

 doses of 1=^11. A number of these patients have been in congestive cardiac 

 failure with obvious oedema. In these patients the latent periods have been 

 found to be considerably longer than would be expected from the observa- 

 tions made on cases not in cardiac failure. 



This dose response system provides a convenient method of assessing either 

 the protective or therapeutic efficacy of a drug for this particular phase of 

 the radiation syndrome. Provided sufficient material is available, it is 

 possible to carry out properly planned clinical trials. In this way the 



231 



