iaea human health series publications - SEDIM

(4) Using the same target–filter and kV combination used for imaging the 45 mm PMMA slab in the AEC test(see Section 8.4.2), make an exposure in manual mode with the previously determined mAs value, mAs AEC . Ifit is not possible to select the exact mAs value, then the kerma (M AEC ) can be estimated by extrapolation froma measurement taken at the closest available manual mAs setting, M 1 , that is:MAECmAs AEC= M1mAsM1(4)(5) Obtain the value of the incident kerma, K i,45 (at the height of the top surface of the 45 mm phantom), fromM AEC using Eqs (5) and (6) and record the value on Chart 11 in Annex II:K i,45 = M AEC ·N mammo · k TP (5)k TP( 273. 2 + T)P0=¥( 273. 2 + T0)P(6)wherek TPN mammoT 0 and P 0is the dosimeter correction factor for temperature and pressure to be used if the dosimeter is avented air ionization chamber;is the value of the calibration factor for beam quality;are the values of temperature and pressure at which the dosimeter is calibrated (if applicable).(6) Repeat steps 4 and 5 for the target, filter, mAs and kV used for 20 and 70 mm PMMA slabs, respectively.(7) For these measurements, correct the incident air kerma value to the location of the entrance surface asfollows:Ê dT- 45ˆKi, 20= Ki,45ËÁd - 20¯˜T2(7)Ê dT- 45ˆKi, 70= Ki,45ËÁd - 70¯˜T2(8)112