Department of Radiation Oncology, Henry Ford Health System, Detroit, MI 48202, USA.
Med Phys. 2012 May;39(5):2518-23. doi: 10.1118/1.3700403.
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.
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.
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%.
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.
提高强度调制放射治疗（IMRT）的剂量计算精度至关重要。我们开发了一种用于生成肺癌患者 IMRT 计划的基于相空间的剂量核的方法。
使用 EGSnrc/BEAMnrc 代码系统模拟了 21EX、6 MV 光子束（加利福尼亚州帕洛阿尔托的瓦里安医疗系统）直线加速器治疗头中的粒子传输。在次级准直器下记录相空间信息。相空间文件中的每个粒子都与一个射束有关，其索引在粒子的 LATCH 变量中计算并保存。DOSXYZnrc 代码被修改为根据其射束索引累积每个粒子沉积的能量。此外，从该射束中所有粒子的方向计算每个射束的中心轴。然后在中心轴周围定义一个圆柱体，以使仅在圆柱体内部沉积的能量被计数。在计数过程中为每个圆柱体建立一个查找表。在模拟肺体模上开发的治疗计划中评估了圆柱形射束能量沉积方法的效率和准确性。
在水中体模中计算的开放正方形射野的轮廓和百分深度剂量与测量值相差在 1.5%以内。使用圆柱形剂量核进行优化的剂量被发现与非截断的 3D 核计算的剂量相差在 0.6%以内。圆柱截断将优化时间减少了约 80%。
开发了一种基于相空间的剂量核生成方法，该方法使用截断的圆柱体进行剂量评分，用于基于射束的肺治疗计划优化，并发现与标准的非截断评分方法非常吻合。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，这对于基于蒙特卡罗的 4D-IMRT 或 IMAT 治疗计划可能很有用。
