A study of interface effects in 60Co beams using a thin-walled parallel plate ionization chamber.
A study of interface effects in 60Co beams using a thin-walled parallel plate ionization chamber.
复制标题
使用薄壁平行板电离室研究 60Co 束中的界面效应。
DOI：
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发表时间：
1992
期刊：
影响因子：
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通讯作者：
Pedro Andreo
中科院分区：
文献类型：
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作者：
Bo Nilsson;Anders Montelius;Pedro Andreo
建立了一个大型平行平面电离室，用于研究60 Co束流的界面效应。所设计的几何形状产生来自侧壁的可忽略不计的扰动，这与市售的平面平行腔室中存在的大的影响相反。该室已被用来调查过渡区的界面现象，使用广泛的元素（Z = 4-82）作为前，后散射介质和临床相关的60钴γ射线场的大小。已经研究了离散地改变腔室高度（0.5-11 mm）和增加壁厚（1-9 mg/cm 2）的影响。测量的电离随实验设置的变化（反向散射材料和室壁之间的气隙，在dmax和5 cm深度处的测量，改变室前面和后面的材料等）。也被调查了。离子室的简单几何形状已被发现最适合用于蒙特卡罗计算的基准研究。离子室是适合于实验研究不同的传输参数的影响，在蒙特卡罗模拟。结果表明，复杂的物理机制，60 Co界面剂量学仍然使蒙特卡罗凝聚历史（宏观）技术不确定。已经发现，EGS 4 Monte Carlo系统，连同用户代码DOSRZ V4.0和PRESTA算法，产生良好的协议与实验低和中等Z（主要兴趣在剂量测定和放射治疗），但可能低估高达10%的背散射从高Z材料，即使当传输参数优化。
A large plane-parallel ionization chamber has been constructed to investigate interface effects in 60Co beam. The designed geometry yields negligible perturbation from the side walls, as opposed to the large effects existing in commercially available plane-parallel chambers. The chamber has been used to investigate interface phenomena in transition zones using a wide range of elements (Z = 4-82) as front- and back-scattering media and a clinically relevant 60Co gamma-ray field size. The effects of varying the chamber height discretely (0.5-11 mm) and increasing the wall thickness (1-9 mg/cm2) have been investigated. The variation of the measured ionization with the experimental setup (air gap between backscatter material and chamber wall, measurements at dmax and at 5-cm depth, varying the material both in front of and behind the chamber, etc.) has also been investigated. The simple geometry of the ion chamber has been found optimum for benchmark studies of Monte Carlo calculations. The ion chamber is suited for investigating experimentally the effects of varying transport parameters used in Monte Carlo simulations. The results presented show that the complex physical mechanisms governing 60Co interface dosimetry still make Monte Carlo condensed-history (macroscopic) techniques uncertain. It has been found that the EGS4 Monte Carlo system, together with the user code DOSRZ V4.0 and the PRESTA algorithm, yields good agreement with experiments for low and medium Z (main interest in dosimetry and radiotherapy), but may underestimate up to 10% the backscatter from high-Z materials even when transport parameters are optimized.