高エネルギーX線のアクリル樹脂ファントムによる吸収線量 測定の際の電離箱の吸収線量変換係数 Absorbed Dose Conversion Factors of Several Ionization Chambers to Determine Absorbed Dose by the Use of Acrylic Plastic Phantom for High Energy X-rays
Absorbed dose conversion factors, (C<SUB>λ</SUB>)<SUB>acryl</SUB> of 8 types of commercially available cylindrical ionization chambers were calculated for conditions using an acrylic plastic phantom and high energy X-rays of 4 MV,6 MV,10 MV and 15 MV and <SUP>60</SUP>Co γ rays. The calculations were according to a Japan Association of Radiological Physicists (JARP) protocol (1986). In comparison with the (C<SUB>λ</SUB>)<SUB>acryl</SUB> for the JARP ionization chamber (C-110) having a wall and build-up cap of acrylic plast ic, the difference for the other 7 ionization chambers is small, being from -1.1% to +0.4%. Among them, the (C<SUB>λ</SUB>)<SUB>acryl</SUB> for the NE 2581 chamber with a wall of A-150 plastic and Lucentine build-up cap is the most different value of about -1.1% and that for the NE 2505/3B chamber with a wall of nylon and acrylic build-up cap is the second most different value of about -0.7%. With a wall and build-up cap of the same acrylic plastic, the difference between PTW 30001 and PTW 23333chambers is very small, being within ±0.1%. In order to compare the absorbed dose given according to the absorbed dose conversion factors calculated, twin ionization chambers were installed in the acrylic plastic intercomparison phantom for each exposure and 5 types, the PTW 30001, JARP C-110, PTW 23333, NE 2571 and NE 2581 chambers were used for 4 MV and 10MV X-rays. The measured absorbed doses for these ionization chambers show good agreement within ±0.35%, although the difference in the measured doses between PTW 30001 and 4 chambers increases from - 0.44% to +0.71%.
放射線医学物理 19(2), 90-98, 1999-06-30
Japan Society of Medical Physics