Ten Haken R K, Awschalom M, Rosenberg I
Med Phys. 1985 Jan-Feb;12(1):46-52. doi: 10.1118/1.595734.
To assess the effect of ionization chamber wall thickness on absolute neutron absorbed dose determinations, measurements were made of the charge collected by an A-150 tissue-equivalent plastic ionization chamber irradiated by a p(66)Be(49) neutron therapy beam as a function of chamber wall thickness both in air and in four different media: tissue-equivalent solution, water, motor oil, and glycerin. Wall thicknesses ranged from 1 to 31 mm, where isolation of the chamber gas volume from protons originating outside the chamber wall was assured. The in-air measurements compare favorably with earlier buildup measurements performed with an A-150 extrapolation chamber in an A-150 phantom. The in-phantom results may be explained if the effect of charged particles reaching the gas volume from the medium and the wall as well as the differences in neutron attenuation by the wall and the medium displaced by the wall are taken into account. The errors in absolute absorbed dose determination caused by ignoring the above processes are assessed.
为评估电离室壁厚度对绝对中子吸收剂量测定的影响，我们进行了相关测量。测量的是一个A - 150组织等效塑料电离室在p(66)Be(49)中子治疗束照射下收集的电荷，该电荷是电离室壁厚度在空气中以及在四种不同介质（组织等效溶液、水、机油和甘油）中的函数。壁厚度范围为1至31毫米，在此范围内可确保电离室气体体积与来自室壁外部的质子隔离。空气中的测量结果与早期在A - 150体模中使用A - 150外推电离室进行的累积测量结果相比很有利。如果考虑到带电粒子从介质和壁到达气体体积的影响，以及壁对中子的衰减和壁所取代的介质对中子衰减的差异，那么体模内的结果就可以得到解释。我们评估了忽略上述过程在绝对吸收剂量测定中所引起的误差。
