Sloboda R S, Wang R
Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada.
Phys Med Biol. 1998 Dec;43(12):3495-507. doi: 10.1088/0031-9155/43/12/008.
Dose rates in a phantom around a shielded and an unshielded vaginal applicator containing Selectron low-dose-rate 137Cs sources were determined by experiment and Monte Carlo simulation. Measurements were performed with thermoluminescent dosimeters in a white polystyrene phantom using an experimental protocol geared for precision. Calculations for the same set-up were done using a version of the EGS4 Monte Carlo code system modified for brachytherapy applications into which a new combinatorial geometry package developed by Bielajew was recently incorporated. Measured dose rates agree with Monte Carlo estimates to within 5% (1 SD) for the unshielded applicator, while highlighting some experimental uncertainties for the shielded applicator. Monte Carlo calculations were also done to determine a value for the effective transmission of the shield required for clinical treatment planning, and to estimate the dose rate in water at points in axial and sagittal planes transecting the shielded applicator. Comparison with dose rates generated by the planning system indicates that agreement is better than 5% (1 SD) at most positions. The precision thermoluminescent dosimetry protocol and modified Monte Carlo code are effective complementary tools for brachytherapy applicator dosimetry.
通过实验和蒙特卡罗模拟确定了在含有Selectron低剂量率137Cs源的屏蔽和未屏蔽阴道施源器周围模体中的剂量率。使用热释光剂量计在白色聚苯乙烯模体中按照针对精度设计的实验方案进行测量。对相同设置使用EGS4蒙特卡罗代码系统的一个版本进行计算，该版本已针对近距离放射治疗应用进行修改，最近还纳入了由比拉耶夫开发的新组合几何包。对于未屏蔽施源器，测量的剂量率与蒙特卡罗估计值在5%（1标准差）范围内一致，同时突出了屏蔽施源器的一些实验不确定性。还进行了蒙特卡罗计算，以确定临床治疗计划所需屏蔽的有效透射值，并估计在与屏蔽施源器相交的轴向和矢状平面上各点处水中的剂量率。与计划系统生成的剂量率进行比较表明，在大多数位置一致性优于5%（1标准差）。精确热释光剂量测定方案和改进的蒙特卡罗代码是近距离放射治疗施源器剂量测定的有效互补工具。
