J. H. MARTIN AND G. MULLER 



normal and high kV conditions, is about 20 per cent. Although high kilo- 

 voltages result in lower skin doses, by a factor of the order of three, the greater 

 penetration of high kV beams mean that more radiation penetrates to the 

 bone marrow. As compared with a previous assessments^ in which no 

 allowance was made for radiation quality, the value now obtained is some 

 18 per cent higher, a difference which is within the order of accuracy of the 

 determination. 



Table 3. Adults 



To the values in Tables 3 and 4 must be added allowances for screening 

 procedures and mass miniature radiography. The final bone-marrow dose 

 becomes about 140 gram-rads or 95 millirads per head of population. 



These figures make it possible to assess the incidence of leukaemia which 

 can be attributed to the use of diagnostic X-rays. Broadly speaking, from a 

 survey of some X-ray diagnostic departments, it can be said that the age 

 distribution of the cases presented does not differ radically from that of the 

 population, and the average number of years at risk is thus 34. Assuming 

 that there is no threshold for the effect, that the integrated dose rather than 

 the dose at any given point is significant, and that the dose administered is 

 cumulative, and these assumptions should be stressed, one finds that the 

 incidence of leukaemia which could possibly be attributed to the use of 

 diagnostic X-rays is some 10 per cent of the 50 per million cases occurring 

 annually, i.e. a total of 50 cases per year in Australia. 



Between 1936 and 1956 the consumption of X-ray film for medical use in 



35 



