Poole — Notes on the Distribution of Activity in Radium Therapy. 4? 



If a larger area has to be treated, an arrangement similar to that of Table 4 

 might be used. Suppose the total dose increased to 300 mc. hrs., the actions 

 would be : — 



Oil the surface of a serum needle 300 x 160 = 48,000 units. 

 At a depth of 5 cms. opposite centre of area of application 300 x 0'26 = VS 

 units. 

 And so on. 



For a single dose with a Hat surface applicator of 6 sq. em. area and 3 mm. 

 thick (brassj,in contact with the skin, the emanation tuhes in the applicator being 

 in contact with the base, and as uniformly distributed as possible, we can use the 

 figures in column J^ of the table in the last paper, multiplying by 10 to allow for 

 the change of units. Thus, for a dose of 300 mc. hrs. the actions would be :■ — 



On skin at centre of applicator 300 x 12-4 = 3,720 units. 

 At a depth of 1 cm. opposite to centre of applicator 300 x 3'6 = 1,080 units. 

 „ 5 cms. „ „ „ 300 X 0-27 = 81 units. 



In this way a comparison may be made between the actions to be expected at 

 various depths with different arrangements and doses. 



As in numerous cases the permissible dose is limited solely by the damage done 

 to the skin or flesh in contact with the applicator, it is interesting to work out 

 the skin action through v,-irious thicknesses of brass in direct contact with the 

 tissues. This is especially important in the case of internal tubular applicators 

 where no intervening material is employed. The figures are shown in Table 5. 

 Here F represents the activity at a fixed distance through t mm. of brass, the bare 

 tube being 1000. D is the external diameter of a tubular applicator of thickness 

 t with a bore of 1 mm. to take a single central capillary. A4 is the skin activity 

 on the surface of such an applicator, or of any applicator, in which only a 

 thickness t of brass is interposed between the emanation tube [assumed 15 mm. 

 long] and the flesh. Aa thus also applies to a single tube in a flat applicator, or 

 a large bore tubular applicator in which the emanation tube rests against one 

 side. 



The figures in columns A.^ to A^ represent approximately the skin activities 

 on the surface of tubular applicators 3 to 7 mm. external diameter and t mm. 

 thick. The interior of the applicator, which in all these cases is at least 2 mm. in 

 diameter, is assumed to contain as many uniformly active capillaries as it will 

 hold, so that the distribution may be regarded as symmetrical. These values are 

 obtained by multiplying the value of Ad for the appropriate diameter by the ratio 

 of the values of F for the thin- and thick-walled tubes respectively. Thus, a tube 

 6 mm. in diameter and 2-5 mm. thick would have a bore of 1 mm., and contain a 

 single emanation capillary. Its surface action would be 50, the value of F being 

 9-7. If its wall was only 0-5 mm. thick, the internal bore would be 5 mm., and 

 would contain a large number of capillaries. The value of i^ for 0-5 mm. being 30, 

 the surface action, A^, is assumed to be 30 x 50 ^ 97, i.e., about 150, as shown in 

 the table. This method is only approximate ; but it seems unlikely that any 

 errors due to it would be comparable with those due to the variations from the 

 assumed conditions which are likely to occur in practice. 



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