GZP型60Co近距离治疗源基于金属施源器剂量参数的蒙特卡罗研究

Monte Carlo dosimetric study of the GZP 60 Co brachytherapy source with stainless steel applicator

目的 研究金属施源器对GZP3型60Co近距离治疗源剂量分布的影响,获得该源基于金属施源器的剂量学参数。方法 通过蒙特卡罗软件Geant4获得近距离治疗源周围（0～10 cm）的平均吸收剂量,并根据AAPM的TG43和TG43U1等报告推荐的计算公式获得该源基于金属施源器的剂量学参数。模拟中60Co近距离治疗源位于半径为30 cm的球体水模中心。结果 获得基于金属施源器的GZP3型60Co近距离治疗源1和2号通道的Λ为1.014 cGyh-1U-1（与无施源器相比分别偏差0.5%）,3号通道的Λ为0.998 cGyh-1U-1（与无施源器相比分别偏差0.1%）;中垂轴0.5～10.0 cm距离范围内的径向剂量函数,并获得该函数的拟合公式;角度0°～175°、距离0.5～10.0 cm范围内的各向异性函数。结论 本研究得到的基于金属施源器的剂量学参数为该源的临床使用提供更加精确的数据参考,在临床使用中应考虑金属施源器对于60Co剂量分布的影响。

Objective To evaluate the effect of stainless steel applicator on dose distribution in GZP 60Co brachytherapy source and to obtain the dosimetric parameters of the 60Co source with stainless steel applicator. Methods Geant4 was employed to obtain the mean adsorption dose of the 60Co brachytherapy source in the range of 0-10 cm, and the dosimetric parameters were calculated according to the formula proposed by AAPM reports TG43 and TG43U1. The 60Co source was located in the center of a sphere water phantom with a radius of 30 cm. Results For channel 1 and 2 of GZP 60Co source, the results of Λ with stainless steel applicator were 1.014 cGyh-1U-1（with a difference of 0.5% compared with non-applicator）, the results of Λ with stainless steel applicator for channel 3 were 0.998 cGyh-1U-1（with a difference of 0.1% compared with non-applicator）. The radial dose function in the range of 0.5-10.0 cm in a longitudinal direction was calculated and the fitting formula for the function was obtained. The polynomial function for the radial dose function and the anisotropy function with a of 0°-175° and an r of 0.5-10.0 cm were obtained. Conclusion The dosimetric parameters of the 60Co source with stainless steel applicator are obtained, which provide more accurate reference data for clinical application. In clinical practice, the effect of stainless steel applicator on dose distribution should be considered.