Mackie T R, el-Khatib E, Battista J, Scrimger J, Van Dyk J, Cunningham J R
Med Phys. 1985 May-Jun;12(3):327-32. doi: 10.1118/1.595691.
We have measured the radiation dose in simple heterogeneous phantoms and compared our results with those obtained by various methods of computation. Dose data were obtained both within and distal to simulated regions of lung in order to test the ratio of tissue-air ratios (TAR), Batho, and equivalent TAR methods. These procedures are used routinely in manual and computer-aided planning of radiation therapy, but have been validated primarily for cobalt-60 radiation. Tests performed with 6- and 15-MV x rays reveal that incorrect doses can be computed within or near to a low-density medium, particularly when the field size is small. In these cases, electronic equilibrium is not achieved in the lateral direction, thereby violating an implicit assumption of all the above calculation methods. We quantify the errors in dose calculation for simple slab phantoms, and support our interpretation with a Monte Carlo simulation in which the energy transported by charged particles away from sites of x-ray interactions is considered directly.
我们已在简单的非均匀体模中测量了辐射剂量，并将我们的结果与通过各种计算方法获得的结果进行了比较。为了测试组织空气比（TAR）、巴托（Batho）和等效TAR方法的比值，在模拟肺区域内部和远端均获取了剂量数据。这些程序在放射治疗的手动和计算机辅助计划中经常使用，但主要是针对钴 - 60辐射进行验证的。用6兆伏和15兆伏的X射线进行的测试表明，在低密度介质内部或附近可能会计算出错误的剂量，特别是当射野尺寸较小时。在这些情况下，在横向方向上未达到电子平衡，从而违反了上述所有计算方法的一个隐含假设。我们对简单平板体模的剂量计算误差进行了量化，并用蒙特卡罗模拟支持我们的解释，在该模拟中直接考虑了带电粒子从X射线相互作用部位带走的能量。
