EXPERIMENTAL LEUKAEMOGENESIS BY RADIATION 



109 



treating ankylosing spondylitis by several exposures weekly at high dose- 

 rate for a few weeks, it will be readily admitted that these experimental 

 dose-response curves have little, if any, direct application to man. They have, 



50 r 



u 25- 



Mortality of 9 CBA mice 12 months after start 



4-week exposure to *°Co v-rays • = 59— 60r/hr 



r.r.r. O = l6-l9r/hr 



1000 r A 



24 (hr) 

 1 (days) 2 4 



Interval between successive doses 



672 



-! \ ^ r 



20 14 7 



Number of doses 



Fig. 2. Mortality in female CBA mice given 1,000 r of ""Co y-rays over a 4-week period at 

 different dose-rates and with different schedules of fractionation. At 12 months practically all 

 deaths were due to leukaemia. 



^ 25 



Mortality of V CBA mice at 12 months after start 

 4-week exposure to *°Co y-rays at 16-19 r/hr 



24 (hr) 



1 (days) 2 4 



Interval between successive doses 



672 



112 



20 



14 

 Number of doses 



Fig. 3. Mortality in female CBA mice given 1,000 r or 2,000 r of ""Co y-rays over a 4- week 

 period at a fixed dose-rate but with different schedules of fractionation. At 12 months practic- 

 ally all deaths were due to leukaemia. 



