RADIATION QUALITY AND BONE-MARROW 

 DOSE IN RADIOLOGY 



J. H. Martin and G. Muller 

 Physics Department, Peter MacCallum Clinic, Melbourne 



It has been realized for many years that ionizini^ radiations can induce 

 leukaemia, but it is only in recent years that its induction in man at low doses 

 has become apparent. This realization arises from evidence of leukaemia 

 among radiologists, that in the survivors of the atomic bomb explosions in 

 Japan, that given in the work of Court-Brown and Doll on the incidence in 

 persons treated for ankylosing spondylitis, the investigation in children 

 treated by X-rays for enlargment of the thymus gland and the much pul^li- 

 cized studies of Alice Stewart and her colleagues relating incidence of 

 leukaemia in children to exposure to diagnostic X-rays in utero. 



These studies have shown the possibility of a linear relationship between 

 incidence of leukaemia and dose of radiation, but the information at low 

 doses is scanty, and it is also possible to assume a threshold. Bone-marrow 

 doses resulting from radiation procedures are, therefore, under study to 

 clarify the situation. 



Some preliminary assessments in various countries of bone-marrow dose 

 due to diagnostic radiology have been made and are referred to in the recent 

 report of the United Nations Scientific Committee on Atomic Radiations^ 



In this paper an endeavour will be made to give a more detailed assessment 

 of the bone-marrow dose taking into account the changes in quality of the 

 radiation as it penetrates a scattering medium such as the body. 



A study has been made of the radiation conditions with regard to cjuality 

 and quantity within the field of radiation, and outside it in regions to which 

 radiation can be scattered. The corrections to be made for the absorption 

 of radiation by the bony shell surrounding the bone marrow, vary very much 

 with the energy of the radiation in the range of energies of interest and a 

 knowledge of the radiation ciuality within the body is thus necessary. 



An assessment of bone-marrow dose has been made first, for the conditions 

 of kilovoltage and filtration considered to be average for diagnostic practice 

 at present. These factors have been determined from a survey of the factors 

 in use by a number of X-ray departments. In addition, an assessment has 

 been made for conditions used with high kilovoltage techniques, a charge 

 of about 30 kV being usual. Radiation quality within the radiation field 

 has been studied using a system whose response is markedly dependent upon 

 energy and comparing the results with those obtained from a non-quality 

 dependent system. The system has been calibrated to yield effective H.V.L. 

 in aluminium as a measure of the quality of the radiation of interest. The 

 result of the qualitv study is shown in Figure 1. 



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