用蒙特卡罗方法评估加速器光子剂量各向异性分析算法的精度

发布时间：2018-11-16 16:39

【摘要】：目的：以蒙特卡罗模拟的结果为基准，评估各向异性分析算法（Anisotropic AnalyticalAlgorithm，AAA）在非均匀介质中的计算精度。方法：建立一包含非均匀介质（空气、肺、脂肪、肌肉、骨）的水模体,模体大小为40cm×40cm×25cm，非均匀介质为30cm×30cm×5cm的平板，位于水模体的5cm深度处。分别用蒙特卡罗方法、AAA算法、笔形束卷积算法（Pencil Beam Convolution，PBC算法）（作为对比）计算不同射野（1cm×1cm到10cm×10cm）、不同能量（6MV和15MV）、不同介质中的深度剂量和离轴比并做比较。深度剂量的比较使用定义的剂量偏差和剂量偏离因子，在非均匀介质区域和非均匀介质后的区域进行。离轴比的比较通过伽马分析来实现。结果：AAA算法在空气介质中、能量分别为6MV和15MV时，剂量偏差的范围分别为40.37%～517.22%、42.55%～560.97%，伽马分析通过率范围分别为12.20%～64.63%、21.95%～65.82%，AAA算法的剂量偏差均小于PBC算法，伽马分析通过率与PBC算法接近。AAA算法在肺介质中、能量分别为6MV和15MV时，剂量偏差的范围分别为-2.54%～11.63%、-0.92%～26.29%，伽马分析通过率范围分别为84.15%～93.90%、87.80%～100.00%，AAA算法除个别射野的剂量偏差大于PBC算法外，其它均小于PBC算法，伽马分析通过率均大于PBC算法。AAA算法在脂肪介质中、能量分别为6MV和15MV时，剂量偏差的范围分别为-2.45%～-1.22%、-3.43%～1.26%，伽马分析通过率范围分别为93.90%～97.56%、93.90%～97.56%，AAA算法除能量为6MV、2cm×2cm射野的剂量偏差大于PBC算法外，其它均小于AAA算法，伽马分析通过率与PBC算法接近。AAA算法在肌肉介质中、能量分别为6MV和15MV时，剂量偏差的范围分别为0.99%～4.03%、1.65%～4.38%，伽马分析通过率范围分别为92.68%～96.34%、95.12～97.56%，AAA算法除能量为15MV时、1cm×1cm射野的剂量偏差小于PBC算法外，其它均大于PBC算法，，伽马分析通过率整体与PBC算法接近。AAA算法在骨介质中、能量分别为6MV和15MV时，剂量偏差的范围分别为1.68%～4.22%、1.47～2.60%，伽马分析通过率范围91.46%～97.56%、92.68%～97.56%，AAA算法在能量为6MV时，剂量偏差均大于PBC算法，伽马分析通过率整体与AAA算法接近，在能量为15MV时，除个别射野的剂量偏差大于PBC算法外，其它均小于PBC算法，伽马分析通过率均与PBC算法接近。结论：AAA算法计算的精度在空气、肺、脂肪介质中高于PBC算法，而在肌肉、骨介质中的精度略低于PBC算法。AAA算法在肺、脂肪介质中剂量计算的结果与蒙特卡罗模拟的结果一致性较好，计算精度较高，但在空气中的剂量计算结果与蒙特卡罗模拟的结果仍偏离较大。AAA算法在能量为6MV时、空气介质、肺介质、脂肪、肌肉介质中剂量计算的精度高于能量为15MV时，而骨介质中剂量计算的精度总体上略低于能量为15MV时。同时，AAA算法，尤其是PBC算法在1cm×1cm射野时显示了较差的计算精度。
[Abstract]:Aim: to evaluate the accuracy of anisotropic analysis algorithm (Anisotropic AnalyticalAlgorithm,AAA) in inhomogeneous media based on Monte Carlo simulation results. Methods: a water motif containing air, lung, fat, muscle and bone was established. The size of the model was 40cm 脳 40cm 脳 25 cm, and the heterogeneous medium was 30cm 脳 30cm 脳 5cm, which was located at the 5cm depth of the water motif. Monte Carlo method, AAA algorithm and pen-beam convolution algorithm (Pencil Beam Convolution,PBC algorithm) are used to calculate and compare the depth dose and off-axis ratio of different fields (1cm 脳 1cm to 10cm 脳 10cm), different energy (6MV and 15MV), and different medium. The depth dose is compared using the defined dose deviation and dose deviation factor in the inhomogeneous medium and the area behind the inhomogeneous medium. The off-axis ratio is compared by gamma analysis. Results: when the energy of AAA algorithm is 6MV and 15MV in air medium, the range of dose deviation is 40.37, 517.22, 42.55 and 560.97, and the passing rate of gamma analysis is 12.20 and 64.63, respectively. 21.95 the dose deviation of 65.82 AAA algorithm is smaller than that of PBC algorithm, and the passing rate of gamma analysis is close to that of PBC algorithm. When AAA algorithm is in lung medium, its energy is 6MV and 15MV, respectively. The range of dose deviations were -2.54 and 11.63- 0.92 and 26.29, respectively, and the passing rate of gamma analysis was 84.15 and 93.900.The range was 87.80 and 100.00. The dose deviation of the AAA algorithm is larger than that of the PBC algorithm, the other is smaller than that of the PBC algorithm, and the passing rate of gamma analysis is higher than that of the PBC algorithm. When the AAA algorithm is in fat medium, the energy is 6MV and 15MV, respectively. The range of dose deviation is -2.45 and 1.22 and 3.430.The passing rate of gamma analysis is 93.90,97.56and 97.90A, respectively. The energy of the AAA algorithm is 6 MV. The dose deviation of 2cm 脳 2cm field is larger than that of PBC algorithm, and the other is smaller than that of AAA algorithm. The passing rate of gamma analysis is close to that of PBC algorithm. When AAA algorithm is in muscle medium, the energy of AAA algorithm is 6MV and 15MV, respectively. The range of dose deviation is 0.99 and 4.03 and 1.65 and 4.38, respectively. The passing rate of gamma analysis is 92.68 and 96.340.95.1297.56A, except for the energy of 15MV. The dose deviation of 1cm 脳 1cm field is smaller than that of PBC algorithm, but the rest is larger than that of PBC algorithm. The overall passing rate of gamma analysis is close to that of PBC algorithm. When AAA algorithm is in bone medium, the energy of AAA algorithm is 6MV and 15MV, respectively. The dose deviation ranges from 1.68 to 4.22 and from 1.47 to 2.60. The gamma-ray analysis pass rate ranges from 91.46 to 97.56 and 92.68 to 97.56A. When the energy is 6MV, The dose deviation is larger than that of PBC algorithm, and the passing rate of gamma analysis is close to that of AAA algorithm. When the energy is 15MV, the dose deviation of individual field is larger than that of PBC algorithm, and the passing rate of gamma analysis is smaller than that of PBC algorithm. The passing rate of gamma analysis is close to that of PBC algorithm. Conclusion: the accuracy of AAA algorithm is higher than that of PBC algorithm in air, lung and fat medium, but the accuracy in muscle and bone medium is slightly lower than that in PBC algorithm. The results of dose calculation in adipose medium are in good agreement with those of Monte Carlo simulation, and the accuracy of calculation is high, but the result of dose calculation in air still deviates greatly from that of Monte Carlo simulation. AAA algorithm is used when the energy is 6MV. The accuracy of dose calculation in air medium, lung medium, fat medium and muscle medium is higher than that in 15MV medium, while that in bone medium is slightly lower than that in 15MV medium. At the same time, the AAA algorithm, especially the PBC algorithm, shows poor accuracy in the field of 1cm 脳 1cm.
【学位授予单位】：南华大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R142

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