256 



BIOLOGICAL EFFECTS OF IONIZING RADIATIONS 



X 



r> 



ft 



lead bricks" / 

 four inches thick 



(a) 



y-rays 



(_sourceS 



concrete or 

 sand bags, 

 two feet thick 



(b) 



Figure 9-9. Protection against ionizing radiations is offered by relatively thin 

 layers of heavy-atom absorbers (a), or by relatively thick layers of lighter-atom 

 absorbers (b). Absorption follows approximately the Beer-Lambert Law (Chap- 

 ter 4): intensity decays exponentially with thickness. Note protective chemicals 

 in pill form! 



The clinical symptoms of radiation sickness caused by the LD 50 are fairly 

 well known: diarrhoea, nausea and vomiting, followed by inflammation of 

 the throat; loss of hair; loss of appetite; fever and pallor; rapid emaciation, 

 and death — completed within 3 to 4 weeks of exposure. For less exposure, 

 recovery begins after a period of time which is longer the greater the ex- 

 posure. Repeated exposures with small doses precipitate the onset of leuke- 

 mia or carcinogenesis, often years after the first exposure. Certain chemi- 

 cals, mentioned earlier in the chapter, offer some protection against the 

 chemical and physical effects which multiply into the biological effects. 

 Further, experiments on the removal of Sr 90 and other radioactive isotopes 

 from the body after ingestion by complexing them away with the so-called 

 chelating (complexing) agents, are showing limited promise. 



Radiation Therapy 



Because they are undergoing more rapid cell division and have certain 

 instabilities which normal cells do not have, cancer cells are, as a general 

 rule, more radiation-sensitive than normal cells. Further, by a continuous 

 rotation of either target or radiation beam, it is a rather simple matter in 

 principle for a radiologist to deliver a high accumulated or total dose to the 

 cancerous volume and at the same time deliver only part of that dose to the 

 noncancerous tissue which surrounds it. Radiation therapy is based on 

 these two principles. 



In many cases 2000 to 7000 rem of local irradiation will kill or sterilize a 

 tumor so that it cannot grow. Machine-produced X rays, gamma rays such 

 as those from the Co 60 "bomb" (Figure 9-10), or radium needles inserted 

 directly into the center of the tumor can be used to give local irradiation. 



