Bahar-Gogani J, Wickman G, Johansson L, Johansson B E
Radiation Physics Department, Umeå University, Sweden.
Med Phys. 1999 Sep;26(9):1932-42. doi: 10.1118/1.598698.
The relative absorbed dose distribution in water around an 192Ir line source of 50 mm length and 0.3 mm diam has been measured using a liquid ionization chamber (LIC). The sensitive volume of the chamber is a cylinder with 3.0 mm diam and a thickness of 1.0 mm. The sensitive medium in the LIC consists of a mixture of two dielectric liquids, tetramethylsilane and isooctane. The mixture has been optimized so that the LIC provides an almost energy-independent response for the radiation qualities present at different distances from the source in water. The measurements were carried out at distances of 2.5-50.0 mm along the source bisector and at distances of 0.0 to +/-40.0 mm along the source axis. The results were compared with measurements made with LiF chips in Solid Water and with calculated data based on an analytical solution to the Sievert integral as well as with Monte Carlo calculations of absolute dose rate in water. Considering the uncertainties involved, the dose distribution measured by the LIC is in reasonably good agreement with the theoretical data as well as the results held with LiF. In comparison with the Monte Carlo calculations the discrepancies range from 0.1% to 18% with the largest differences at points close to the source. This work demonstrates the ability of the LIC for mapping the dose distribution around a low-dose-rate brachytherapy source emitting photons of intermediate energies.
使用液体电离室（LIC）测量了长度为50 mm、直径为0.3 mm的192Ir线源周围水中的相对吸收剂量分布。该电离室的灵敏体积是一个直径为3.0 mm、厚度为1.0 mm的圆柱体。LIC中的灵敏介质由两种介电液体（四甲基硅烷和异辛烷）的混合物组成。对该混合物进行了优化，以便LIC对水中距源不同距离处存在的辐射品质提供几乎与能量无关的响应。测量是沿着源平分线在2.5 - 50.0 mm的距离处以及沿着源轴在0.0至±40.0 mm的距离处进行的。将结果与在固体水（Solid Water）中用LiF芯片进行的测量结果、基于西弗特积分（Sievert integral）解析解的计算数据以及水中绝对剂量率的蒙特卡罗计算结果进行了比较。考虑到所涉及的不确定性，LIC测量的剂量分布与理论数据以及LiF测量结果相当吻合。与蒙特卡罗计算结果相比，差异范围为0.1%至18%，在靠近源的点处差异最大。这项工作证明了LIC能够绘制低剂量率近距离放射治疗源周围的剂量分布，该源发射中等能量的光子。
