Cunningham J R, Schulz R J
Med Phys. 1984 Sep-Oct;11(5):618-23. doi: 10.1118/1.595643.
A method for the selection of average stopping-power (L/rho)medair and energy-absorption coefficient (mu en/rho)medair ratios has been developed. The quality of the x-ray beam is characterized by the ratio of ionization chamber readings at depths of 20 and 10 cm in water (TMR)2010. For convenience, a relationship is established between experimental (TMR)2010 and the nominal accelerating potential (MV) of the accelerator. Experimental (TMR)2010 are related to (L/rho)medair and (mu en/rho)medair in a three-step process. First, using experimental and theoretical spectra in the range 60Co to 45 MV, (TMR)2010 were calculated for primary and first-scatter photons, and a graph of experimental versus calculated (TMR)2010 for these same spectra was constructed. Second, (L/rho)medair and (mu en/rho)medair were calculated for a large number of primary spectra [for most of which experimental (TMR)2010 were not available] and a graph constructed that related these quantities and (TMR)2010 calculated as above for this group of spectra. Third, using the graphs from the preceding steps, graphs relating the calculated (L/rho)medair and (mu en/rho)medair with experimental (TMR)2010 were constructed. Data are presented for water, polystyrene, acrylic, graphite, A-150, C-552, Bakelite, and nylon for beams with nominal accelerating potentials in the range 2-45 MV.
已开发出一种选择平均阻止本领（L/ρ）medair和能量吸收系数（μen/ρ）medair比值的方法。X射线束的品质由水模体中20cm和10cm深度处电离室读数的比值（TMR）2010来表征。为方便起见，建立了实验（TMR）2010与加速器标称加速电位（MV）之间的关系。实验（TMR）2010通过三步过程与（L/ρ）medair和（μen/ρ）medair相关。首先，利用60Co至45MV范围内的实验和理论能谱，计算初级光子和一次散射光子的（TMR）2010，并构建这些相同能谱的实验（TMR）2010与计算值的关系图。其次，针对大量初级能谱计算（L/ρ）medair和（μen/ρ）medair[其中大多数没有实验（TMR）2010数据]，并构建将这些量与上述针对该组能谱计算的（TMR）2010相关联的关系图。第三，利用前几步的关系图，构建将计算得到的（L/ρ）medair和（μen/ρ）medair与实验（TMR）2010相关联的关系图。给出了标称加速电位在2 - 45MV范围内的射束在水、聚苯乙烯、丙烯酸、石墨、A - 150、C - 552、酚醛塑料和尼龙中的数据。
