Sahoo S, Selvam T Palani, Vishwakarma R S, Chourasiya G
Radiological Physics and Advisory Division, Health Safety, and Environment Group, Bhabha Atomic Research Centre, Mumbai - 400 094, India.
J Med Phys. 2010 Jan;35(1):15-22. doi: 10.4103/0971-6203.58779.
The reference medium for brachytherapy dose measurements is water. Accuracy of dose measurements of brachytherapy sources is critically dependent on precise measurement of the source-detector distance. A solid phantom can be precisely machined and hence source-detector distances can be accurately determined. In the present study, four different solid phantom materials such as polymethylmethacrylate (PMMA), polystyrene, Solid Water, and RW1 are modeled using the Monte Carlo methods to investigate the influence of phantom material on dose rate distributions of the new model of BEBIG (60)Co brachytherapy source. The calculated dose rate constant is 1.086 +/- 0.06% cGy h(-1) U(-1) for water, PMMA, polystyrene, Solid Water, and RW1. The investigation suggests that the phantom materials RW1 and Solid Water represent water-equivalent up to 20 cm from the source. PMMA and polystyrene are water-equivalent up to 10 cm and 15 cm from the source, respectively, as the differences in the dose data obtained in these phantom materials are not significantly different from the corresponding data obtained in liquid water phantom. At a radial distance of 20 cm from the source, polystyrene overestimates the dose by 3% and PMMA underestimates it by about 8% when compared to the corresponding data obtained in water phantom.
近距离放射治疗剂量测量的参考介质是水。近距离放射治疗源剂量测量的准确性严重依赖于源 - 探测器距离的精确测量。固体模体可以精确加工，因此可以准确确定源 - 探测器距离。在本研究中，使用蒙特卡罗方法对四种不同的固体模体材料，如聚甲基丙烯酸甲酯（PMMA）、聚苯乙烯、固态水和RW1进行建模，以研究模体材料对新型BEBIG（60）Co近距离放射治疗源剂量率分布的影响。对于水、PMMA、聚苯乙烯、固态水和RW1，计算得到的剂量率常数为1.086 +/- 0.06% cGy h(-1) U(-1)。研究表明，模体材料RW1和固态水在距源20 cm范围内表现出水等效性。PMMA和聚苯乙烯分别在距源10 cm和15 cm范围内表现出水等效性，因为在这些模体材料中获得的剂量数据差异与在液体水模体中获得的相应数据没有显著差异。在距源20 cm的径向距离处，与在水模体中获得的相应数据相比，聚苯乙烯高估剂量3%，而PMMA低估剂量约8%。
