. The American journal of roentgenology, radium therapy and nuclear medicine . aa oy Fig. 6. can be applied to other machines withoutintroducing a large error. Glasser, O. .■\m. J. Roentgenol., May. 1923, x, 405. The Economics of Dosimetry in Radiotherapy 959 Before leaving this subject we wish topoint out the simplicity of using the equa-tion. In the first place very little thinking isrequired. The radiologist simply writes downthe data of the problem as shown below: Target-skin distance X = 60 cm. ffor instance)Tissue depth Z = 10 cm. Thickness of Cu. filter t = of field A = 200
. The American journal of roentgenology, radium therapy and nuclear medicine . aa oy Fig. 6. can be applied to other machines withoutintroducing a large error. Glasser, O. .■\m. J. Roentgenol., May. 1923, x, 405. The Economics of Dosimetry in Radiotherapy 959 Before leaving this subject we wish topoint out the simplicity of using the equa-tion. In the first place very little thinking isrequired. The radiologist simply writes downthe data of the problem as shown below: Target-skin distance X = 60 cm. ffor instance)Tissue depth Z = 10 cm. Thickness of Cu. filter t = of field A = 200 sq. cm. he sets down r^ = rio = Similarlyhe looks up the value of b(;o,2oo in TableXIII. The desired value is found in the linefor X = 60 and the column for A = is Therefore bxA = = In Table XVI he finds the valuefor aio,2oo at the intersection of the linefor z = 10 and the column for A = azA = aio,2oo = i-20. In a similar manner he finds the valueof fifl. in Table XVII at the intersectionof the line for Z = 10 and t = Then he writes down the symbols for thefactors with the proper subscripts, thus:rz = r,o (Z = 10)hxA = (X = 60, A = 200)azA = CZ. = 10, A = 200)fzt = (Z = 10, t = )He is now ready to look up the propervalues for these constants from the tablesgiven. Thus in Table XV, for z = 10 hefinds for the value of rio. Therefore That is fzt = fio. = Substituting these values into the equa-tion he finds the amount of radiation forthese conditions in terms of the unitadopted here. R = ^ ^° ,„ X X X (60 + 10)- X = In practice he would write the value next to the symbol inthe above list. This, however, would cause confusion in thisexplanation. 960 The Economics of Dosimetry in Radiotherapy i- \\, :< Siilliii -. -— : ^ depth
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