School of Mechanical Engineering, Shiraz University, Shiraz, Iran.
J Appl Clin Med Phys. 2011 May 19;12(3):3480. doi: 10.1120/jacmp.v12i3.3480.
In this study, dose rate distribution around a spherical 137Cs pellet source, from a low-dose-rate (LDR) Selectron remote afterloading system used in gynecological brachytherapy, has been determined using experimental and Monte Carlo simulation techniques. Monte Carlo simulations were performed using MCNP4C code, for a single pellet source in water medium and Plexiglas, and measurements were performed in Plexiglas phantom material using LiF TLD chips. Absolute dose rate distribution and the dosimetric parameters, such as dose rate constant, radial dose functions, and anisotropy functions, were obtained for a single pellet source. In order to investigate the effect of the applicator and surrounding pellets on dosimetric parameters of the source, the simulations were repeated for six different arrangements with a single active source and five non-active pellets inside central metallic tubing of a vaginal cylindrical applicator. In commercial treatment planning systems (TPS), the attenuation effects of the applicator and inactive spacers on total dose are neglected. The results indicate that this effect could lead to overestimation of the calculated F(r,θ), by up to 7% along the longitudinal axis of the applicator, especially beyond the applicator tip. According to the results obtained in this study, in a real situation in treatment of patients using cylindrical vaginal applicator and using several active pellets, there will be a large discrepancy between the result of superposition and Monte Carlo simulations.
在这项研究中，使用实验和蒙特卡罗模拟技术确定了来自用于妇科近距离放射治疗的低剂量率（LDR）Selectron 远程后装系统的球形 137Cs 丸源周围的剂量率分布。使用 MCNP4C 代码对单个丸源在水中介质和有机玻璃中进行了蒙特卡罗模拟，并且在有机玻璃体模材料中使用 LiF TLD 芯片进行了测量。获得了单个丸源的绝对剂量率分布和剂量学参数，例如剂量率常数、径向剂量函数和各向异性函数。为了研究施源器和周围丸源对源的剂量学参数的影响，针对中央金属管内的单个有源源和五个无源丸源的六种不同排列，重复了模拟。在商业治疗计划系统（TPS）中，施源器和非活性间隔物对总剂量的衰减效应被忽略。结果表明，该效应可能导致计算的 F(r,θ)沿施源器的纵轴高估，尤其是在施源器尖端之外，最大可达 7%。根据本研究的结果，在使用圆柱形阴道施源器并使用多个有源丸源对患者进行实际治疗的情况下，叠加和蒙特卡罗模拟的结果之间会存在很大差异。
