Generation of a novel phase-space-based cylindrical dose kernel for IMRT optimization.
Generation of a novel phase-space-based cylindrical dose kernel for IMRT optimization.
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DOI：
10.1118/1.3700403
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发表时间：
2012-05
期刊：
影响因子：
3.8
通讯作者：
H. Zhong;I. Chetty
中科院分区：
文献类型：
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作者：
H. Zhong;I. Chetty
目的提高剂量计算精度是调强放射治疗(IMRT)的关键。我们开发了一种生成基于相空间的剂量核的方法，用于肺癌患者的调强放疗计划。方法用EGSnrc/BEAMnrc程序模拟了2 1EX、6 MV光子束(加利福尼亚州帕洛阿尔托瓦里安医疗系统)直线加速器治疗头中的粒子输运。在次级颌骨下记录相空间信息。相空间文件中的每个粒子都与一个Beamlet相关联，该Beamlet的索引被计算并保存在粒子的闩锁变量中。DOSXYZnrc程序被修改为根据每个粒子的Beamlet指数来累积每个粒子沉积的能量。此外，根据每个Beamlet中所有粒子的方向计算出每个Beamlet的中心轴。然后围绕中心轴定义一个圆柱体，以便只计算沉积在圆柱体内的能量。在清点过程中，为每个圆柱体建立了查询表。通过在模拟肺模型上开发的治疗计划，评估了柱形射束能量沉积方法的效率和准确性。结果在水模中计算的开放正方形野大小的剖面剂量和深度百分比剂量在测量值的1.5%以内。用圆柱形剂量核优化的剂量与用非截断3D核计算的剂量相比，在0.6%以内。柱面截断使优化时间减少了约80%。结论在基于Beamlet的肺治疗计划优化中，提出了一种基于相空间的剂量核生成方法，该方法使用截断柱体进行剂量计分，与标准的非截断计分方法具有很好的一致性。与以前的技术相比，我们的方法大大减少了计算时间和内存需求，这可能对基于蒙特卡洛的4D调强放疗或IMAT治疗规划有用。
PURPOSE Improving dose calculation accuracy is crucial in intensity-modulated radiation therapy (IMRT). We have developed a method for generating a phase-space-based dose kernel for IMRT planning of lung cancer patients. METHODS Particle transport in the linear accelerator treatment head of a 21EX, 6 MV photon beam (Varian Medical Systems, Palo Alto, CA) was simulated using the EGSnrc/BEAMnrc code system. The phase space information was recorded under the secondary jaws. Each particle in the phase space file was associated with a beamlet whose index was calculated and saved in the particle's LATCH variable. The DOSXYZnrc code was modified to accumulate the energy deposited by each particle based on its beamlet index. Furthermore, the central axis of each beamlet was calculated from the orientation of all the particles in this beamlet. A cylinder was then defined around the central axis so that only the energy deposited within the cylinder was counted. A look-up table was established for each cylinder during the tallying process. The efficiency and accuracy of the cylindrical beamlet energy deposition approach was evaluated using a treatment plan developed on a simulated lung phantom. RESULTS Profile and percentage depth doses computed in a water phantom for an open, square field size were within 1.5% of measurements. Dose optimized with the cylindrical dose kernel was found to be within 0.6% of that computed with the nontruncated 3D kernel. The cylindrical truncation reduced optimization time by approximately 80%. CONCLUSIONS A method for generating a phase-space-based dose kernel, using a truncated cylinder for scoring dose, in beamlet-based optimization of lung treatment planning was developed and found to be in good agreement with the standard, nontruncated scoring approach. Compared to previous techniques, our method significantly reduces computational time and memory requirements, which may be useful for Monte-Carlo-based 4D IMRT or IMAT treatment planning.