Büyükyıldız Mehmet, Kurudirek Murat
a Faculty of Engineering, Department of Electrical and Electronics , Yalova University , Yalova , Turkey.
b Faculty of Science, Department of Physics , Ataturk University , Erzurum , Turkey.
Int J Radiat Biol. 2018 Jan;94(1):70-78. doi: 10.1080/09553002.2018.1403057. Epub 2017 Nov 30.
In this paper, the effective atomic numbers (Z), electron densities (N), exposure buildup factor (EBF) and energy absorption buildup factor (EABF) of healthy (H), carcinoma (C) and equivalent (E) breast tissues were investigated to quantify differences in radiological parameters between the tissues in the continuous energy region. For these purposes, Zs and Ns, of healthy, carcinoma and equivalent (H-C-E) breast tissues were calculated for interaction of gamma rays and charged particles with selected tissues. EBFs and EABFs of the tissues were also calculated for gamma rays as well and were compared to each other for different photon energies (0.015-15 MeV) up to 40 mfp.
A well-known interpolation procedure has been used for the calculation of Z using the mass stopping powers and mass attenuation coefficients for charged and uncharged radiations in the continuous energy region. And the buildup factors of the tissues were calculated by the well-known G-P fitting method based on the interpolation from the equivalent atomic number (Z).
The variation of Zs, Ns with energy and differences (%) in the Zs between the tissues were determined for photon, electron, proton and C ion, which is commonly used in hadron therapy in the relevant energy region 1 keV-400 MeV. Differences (%) between healthy and carcinoma tissues in Z were around 9%, >4%, >5%, >2.5% for C ion, photon, electron and proton interaction, respectively. The relative differences (RD %) in Z between healthy and equivalent tissues in the energy range 0.02-1 MeV were found to be less than 1% for photons and C ions. In addition differences (%) between healthy and carcinoma tissues in EABF and EBF were around 25%, but differences (%) between healthy and equivalent tissues were <6% and <4% (at 40 mfp) in the continuous energy region.
From the results, BR12 was found the be available for an equivalent to healthy breast tissue in 0.02-1 MeV for photons and C ions due to RD (%) in Z between healthy and equivalent tissues (less than 1%). However, for electron interaction, the RD (%) in Z between healthy and equivalent tissues was always greater than 4% in the entire energy range, thus BR12 was found the worse an equivalent to healthy breast tissue in in the entire energy range for electron. Also the reported data in the study should be useful to choose best equivalence for photon, electron, proton and Carbon ion interactions.
本文研究了健康（H）、癌（C）和等效（E）乳腺组织的有效原子序数（Z）、电子密度（N）、照射积累因子（EBF）和能量吸收积累因子（EABF），以量化连续能量区域中各组织间放射学参数的差异。为此，计算了γ射线和带电粒子与选定组织相互作用时健康、癌和等效（H-C-E）乳腺组织的Z值和N值。还计算了各组织对γ射线的EBF和EABF，并针对高达40个平均自由程的不同光子能量（0.015 - 15 MeV）进行了相互比较。
采用一种知名的插值程序，利用连续能量区域中带电和不带电辐射的质量阻止本领和质量衰减系数来计算Z值。并基于等效原子序数（Z）的插值，通过知名的G-P拟合方法计算组织的积累因子。
确定了光子、电子、质子和碳离子（强子治疗中常用）在相关能量区域1 keV - 400 MeV内，Z值和N值随能量的变化以及各组织间Z值的差异（%）。对于碳离子、光子、电子和质子相互作用，健康组织与癌组织之间Z值的差异（%）分别约为9%、>4%、>5%、>2.5%。在0.02 - 1 MeV能量范围内，健康组织与等效组织之间Z值的相对差异（RD%）对于光子和碳离子小于1%。此外，在连续能量区域中，健康组织与癌组织之间EABF和EBF的差异（%）约为25%，但健康组织与等效组织之间的差异（%）在40个平均自由程时<6%和<4%。
结果表明，由于健康组织与等效组织之间Z值的相对差异（RD%）（小于1%），在0.02 - 1 MeV能量范围内，对于光子和碳离子，BR12可作为等效于健康乳腺组织的材料。然而，对于电子相互作用，在整个能量范围内，健康组织与等效组织之间Z值的相对差异（RD%）始终大于4%，因此在整个能量范围内，BR12作为等效于健康乳腺组织的材料较差。此外，本研究报告的数据对于选择光子、电子、质子和碳离子相互作用的最佳等效材料应是有用的。
