• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Medical Physics >Final Aperture Superposition Technique applied to fast calculation of electron output factors and depth dose curves.
【24h】

Final Aperture Superposition Technique applied to fast calculation of electron output factors and depth dose curves.

机译：最终孔径叠加技术适用于快速计算电子输出因子和深度剂量曲线。

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The Final Aperture Superposition Technique (FAST) is described and applied to accurate, near instantaneous calculation of the relative output factor (ROF) and central axis percentage depth dose curve (PDD) for clinical electron beams used in radiotherapy. FAST is based on precalculation of dose at select points for the two extreme situations of a fully open final aperture and a final aperture with no opening (fully shielded). This technique is different than conventional superposition of dose deposition kernels: The precalculated dose is differential in position of the electron or photon at the downstream surface of the insert. The calculation for a particular aperture (x-ray jaws or MLC, insert in electron applicator) is done with superposition of the precalculated dose data, using the open field data over the open part of the aperture and the fully shielded data over the remainder. The calculation takes explicit account of all interactions in the shielded region of the aperture except the collimator effect: Particles that pass from the open part into the shielded part, or visa versa. For the clinical demonstration, FAST was compared to full Monte Carlo simulation of 10 x 10, 2.5 x 2.5, and 2 x 8 cm2 inserts. Dose was calculated to 0.5% precision in 0.4 x 0.4 x 0.2 cm3 voxels, spaced at 0.2 cm depth intervals along the central axis, using detailed Monte Carlo simulation of the treatment head of a commercial linear accelerator for six different electron beams with energies of 6-21 MeV. Each simulation took several hours on a personal computer with a 1.7 Mhz processor. The calculation for the individual inserts, done with superposition, was completed in under a second on the same PC. Since simulations for the pre calculation are only performed once, higher precision and resolution can be obtained without increasing the calculation time for individual inserts. Fully shielded contributions were largest for small fields and high beam energy, at the surface, reaching a maximum of 5.6% at 21 MeV. Contributions from the collimator effect were largest for the large field size, high beam energy, and shallow depths, reaching a maximum of 4.7% at 21 MeV. Both shielding contributions and the collimator effect need to be taken into account to achieve an accuracy of 2%. FAST takes explicit account of the shielding contributions. With the collimator effect set to that of the largest field in the FAST calculation, the difference in dose on the central axis (product of ROF and PDD) between FAST and full simulation was generally under 2%. The maximum difference of 2.5% exceeded the statistical precision of the calculation by four standard deviations. This occurred at 18 MeV for the 2.5 x 2.5 cm2 field. The differences are due to the method used to account for the collimator effect.
机译：描述了最终孔径叠加技术（FAST），并将其应用于放射治疗中临床电子束的相对输出因子（ROF）和中心轴百分比深度剂量曲线（PDD）的近似，即时计算。 FAST基于完全打开的最终光圈和没有打开的最终光圈（完全屏蔽）这两种极端情况下在选定点的剂量预先计算。该技术不同于常规的剂量沉积核心叠加技术：预先计算的剂量与插件下游表面的电子或光子位置不同。特定孔径（X射线钳口或MLC，插入电子施放器中）的计算是通过将预先计算的剂量数据叠加在一起进行的，使用孔径的开口部分上的开场数据和其余部分上的完全屏蔽的数据。该计算明确考虑了光圈屏蔽区域中除准直器效应以外的所有相互作用：从开放部分进入屏蔽部分的粒子，反之亦然。为了进行临床演示，将FAST与10 x 10、2.5 x 2.5和2 x 8 cm2刀片的完整Monte Carlo模拟进行了比较。使用商用线性加速器对6个能量为6的不同电子束的治疗头的详细蒙特卡罗模拟，在0.4 x 0.4 x 0.2 cm3体素中，沿中心轴以0.2 cm的深度间隔计算了剂量的0.5％精度。 -21 MeV。每次模拟在配备1.7 Mhz处理器的个人计算机上花费了几个小时。在同一台PC上，不到一秒钟即可完成叠加的单个刀片的计算。由于预计算的仿真仅执行一次，因此无需增加单个刀片的计算时间即可获得更高的精度和分辨率。对于小场和远光能量，在表面完全屏蔽的贡献最大，在21 MeV时最大达到5.6％。对于大的场尺寸，高的束能量和浅的深度，准直器效应的贡献最大，在21 MeV时最大达到4.7％。为了达到2％的精度，必须同时考虑屏蔽作用和准直器效应。 FAST明确考虑了屏蔽作用。将准直器效应设置为FAST计算中最大的场，FAST和完全模拟之间的中心轴剂量（ROF和PDD乘积）的差异通常在2％以下。 2.5％的最大差异超出了计算的统计精度四个标准偏差。对于2.5 x 2.5 cm2的场，这种情况发生在18 MeV。差异归因于用于考虑准直器效果的方法。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号