CONSIDERATION ON FILM DOSIMETRY FOR MEASURING DOSE DISTRIBUTION OF COBALT-60 BEAM RADIATION

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  • フィルム法によるコバルト60γ線の線量分布測定法の検討
  • フィルムホウ ニ ヨル コバルト 60 ガンマセン ノ センリョウ ブンプ ソクテイホウ ノ ケントウ

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Using the chamber and film method, the depth dose of cobalt-60 γ-rays was measured and compared. In film method, Fuji nomal gravure film (TAC-135), which could be dealt with automatic film processor, was applied The results obtained are as follows : 1) In the stationary exposure of 10×10 cm field size, the film method has a density-exposure dependence on the depth from the surface of phantom. When film of maximum density of 1.5 and the characteristic curve (density vs exposure) in 20 cm deep of the phantom are used, the difference between isodose distribution by film method and depth dose rate by chamber method is almost negligible up to 50% depth dose. 2) In the moving field exposures of 10 cm field size using 20,25 and 30 cmφ phantoms, the difference of the isodose distributions between the film (about 1.5 maximum density) and chamber method is less than ±5% in the region up to the depth of 50% isodose distribution. 3) In both the moving (abdomen and breast, etc) and wedge field exposure, which are clinically applicable, the difference of the isodose distributions between film and chamber method is the same to the results in (2). It is concluded from these results that film method is suitable for the region up to 50% isodose distribution.

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