Mauceri T, Kase K
Med Phys. 1987 Jul-Aug;14(4):653-6. doi: 10.1118/1.596034.
Traditionally, measurements have been made in heterogeneous phantoms to determine the factors which should be applied to dose calculations, when calculating a dose to a heterogeneous medium. Almost all measurements have relied on relatively thin-walled ion chambers, with no attempt to match ion chamber wall material to the measuring medium. The recent AAPM dosimetry protocol has established that a mismatch between ion chamber wall and phantom material can have an effect on dose measurement. To investigate the affect of this mismatch of ion chamber wall material to phantom material, two parallel-plate ion chambers were constructed. One ion chamber from solid water, for measurements in a solid water phantom and the other from plastic lung material, for measurements in a plastic lung material phantom. Correction factors measured by matching ion chamber to media were compared to correction factors measured by using a thin-walled cavity ion chamber with no regard for matching wall and media for cobalt-60, 6-, 10- and 20-MV photon beams. The results demonstrated that the matching of ion chamber to measuring media can be ignored, provided that a small, approximately tissue-equivalent, thin-walled ion chamber is used for measuring the correction factors.
传统上，人们在非均匀模体中进行测量，以确定在计算非均匀介质剂量时应应用于剂量计算的因素。几乎所有测量都依赖于相对薄壁的电离室，而没有尝试使电离室壁材料与测量介质相匹配。美国医学物理师协会（AAPM）最近的剂量测定协议表明，电离室壁与模体材料之间的不匹配会对剂量测量产生影响。为了研究电离室壁材料与模体材料这种不匹配的影响，制作了两个平行板电离室。一个由固体水制成，用于在固体水模体中进行测量，另一个由塑料肺材料制成，用于在塑料肺材料模体中进行测量。将通过使电离室与介质匹配测量得到的校正因子，与使用薄壁腔电离室（不考虑壁与介质匹配）测量得到的校正因子进行比较，用于钴 - 60、6兆伏、10兆伏和20兆伏光子束。结果表明，如果使用一个小的、近似组织等效的薄壁电离室来测量校正因子，那么电离室与测量介质的匹配可以忽略不计。
