不同空腔厚度模体对上段食管癌剂量验证的影响

目的 研究Monaco TPS 中2种计算方法对自制不同空腔厚度模体的剂量计算准确性，并分析不同空腔厚度模体对上段食管癌剂量验证的影响。方法 将不同空腔厚度的模体放在CT模拟定位机上进行扫描获取图像，在Monaco TPS中对获取的图像添加以电离室插口为中心、能量为6 MV、100 MU和不同方野大小的照射野，用2种算法计算电离室空腔的剂量，并在同等条件下用剂量仪在加速器上进行测量。同时在接受固定野动态调强的上段食管癌患者中随机选取20例纳入研究对象，并用2种算法在不同空腔厚度模体上进行剂量验证，结果用SPSS 22.0软件进行统计分析。结果 Monte Carlo和Pencil Beam2种算法在不同空腔厚度模体计算中，计算值与测量值最大偏差分别为0.66%和-1.8%。Monte Carlo算法中RD组配对t检验结果P > 0.05，AD（0 mm，10 mm）、（5 mm，10 mm）和（10 mm，20 mm）组配对t检验P < 0.05，最大偏差为1.1%，其余组P > 0.05；Pencil Beam算法中RD（0 mm，20 mm）和（5 mm，20 mm）组配对t检验结果P < 0.05，最大偏差为0.58%，其余组P > 0.05，AD组P < 0.05，最大偏差为2.78%；2种算法间配对t检验P < 0.05，RD和AD组中最大偏差分别为2.49%和4.14%。结论 Monte Carlo算法计算准确且剂量验证γ通过率高，不同空腔厚度模体间的剂量验证γ通过率无临床差异，在空腔模体计算中不推荐使用Pencil Beam算法。

Effect of phantoms with different cavity thickness on dose verificationupper esophageal cancer

Objective To investigate the dose calculation accuracy of two algorithms in Monaco TPS for self-made phantoms with different cavity thickness, and analyze the influence of phantoms with different cavity thickness on dose verification of upper esophageal cancer.Methods The phantoms with different cavity thickness were placed on the simulated CT positioning machine to scan and acquire images. In Monaco TPS, the irradiation fields with energy of 6 MV, 100 MU and different square field sizes were added to the acquired images. The dose of the cavity of the ionization chamber was calculated by two algorithms, and measured on the accelerator by dosimeter under the same conditions. At the same time, 20 patients with upper esophageal cancer who received dynamic intensity modulation in fixed field were randomly selected and included in the study, and two algorithms were used for dose verification on phantoms with different cavity thickness. The results were statistically analyzed by SPSS 22.0 software.Results The maximum deviations between the calculated values and the measured values were 0.66% and -1.8%, in the calculation of phantoms with different cavity thickness by algorithms of Monte Carlo and Pencil Beam. In Monte Carlo algorithm, the result of RD pair t test is P > 0.05. Paired t test of AD (0 mm, 10 mm), (5 mm, 10 mm) and (10 mm, 20 mm) groups showed no significant difference (P < 0.05). The maximum deviation was 1.1%, and the rest groups were not statisticely significant (P > 0.05); In Pencil Beam algorithm the t test results of RD (0 mm, 20 mm) and (5 mm, 20 mm) pairs were (P < 0.05), the maximum deviation was 0.58%, and the rest groups were (P > 0.05). In AD group, (P < 0.05), the maximum deviation was 2.78%; The paired t test between the two algorithms was (P < 0.05), and the maximum deviations in RD and AD groups were 2.49% and 4.14%, respectively.Conclusion Monte Carlo algorithm has accurate calculation and high gamma pass rate of dose verification, and there is no clinical difference in gamma pass rate of dose verification among phantoms with different cavity thickness, pencil Beam algorithm is not recommended in cavity phantom calculation.