. La revue américaine de roentgoenologie, de radium thérapie et de médecine nucléaire . 1100 100 100 TROP 100 100 230 82.3 82.0 81.0 81.5 81.8 81.8 121 70.0 68.6 68.7 68.5 68.5 68.6 37.8 48.1 49 4 49 6 48.9 49-3 49 3 nous sommes impatients de ne pas transmettre une faute de la formulation de cette généralisation. Nous souhaitons donc porter une attention particulière aux limites de son applicabilité.les données expérimentales sur lesquelles il est couvert les plages suivantes: Distance,52.7 à 73.5 cm.; filtre, 0.42 mm. Cu. À 1,68 mm. Cu., également 3.27 mm. AL ; surface de la peau, 40 cm2. À 1000 cm2., les champs beingrectangulaires avec
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. The American journal of roentgenology, radium therapy and nuclear medicine . 1100 100 100 TOO 100 100 230 82.3 82.0 81.0 81.5 81.8 81.8 121 70.0 68.6 68.7 68.5 68.5 68.6 37.8 48.1 49 4 49 6 48.9 49-3 49 3 We are anxious not to convey a wrongimpression by the wording of this generali-zation. We wish to call particular attention, therefore, to the limits of its applicability.The experimental data on which it is basedcovered the following ranges: Distance, 52.7 to 73.5 cm.; filter, 0.42 mm. Cu. to1.68 mm. Cu., also 3.27 mm. AL; skin area, 40 sq. cm. to 1000 sq. cm., the fields beingrectangular with sides approximately in theratio of iio; water depth, o to 10 cm. inthe phantom already described. In addi-tion, several special experiments were madeto extend the range of the skin areas downto 20 sq. cm. and the range of the tissuedepth to 15 cm. Within these limits forthe different factors, therefore, the abovegeneralization holds with a considerabledegree of accuracy. That the limits can beextended somewhat on either side withoutintroducing a large error can be readily. J- Suf face :, , 2.- « sna depth Lrficr or i5Vi//v Ah-f/i oij (Lffect iS trijefjctxhritof filter /■go i>Hin /^rsa. i.yi Jq. Cm sQo: yitjo , /oao Fig. 2. We may make now the first generalization:A. The effect of the si/.e of the field on theradiation effective at any particular tissuedepth is the same for all filters and alldistances used in practice. granted. The final results are showngraphically in Figure 2. This supplies thenecessary quantitative data to make theproper corrections in the dose according tothe size of the skin area irradiated. 948 The Economics of Dosimetry in Radiotherapy 2. The Effect of the Filter on the Amount of Radiation Effective at Different Depths Table IV EFFECT OF FILTER ON SURFACE RADIATION 200 kv. (crest value) 4 ma., 73.5 cm. T-S DistanceIonization Chamber Half Submerged Area on Surface of Water, in Copper sq. cm. Filter Average mm. 41.5 118 237 1000 0 412 405 397 387 4
