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相关概念视频

Beams with Unsymmetric Loadings01:17

Beams with Unsymmetric Loadings

112
Analyzing a supported beam under unsymmetrical loadings is essential in structural engineering to understand how beams respond to varied force distributions. This analysis involves calculating the deflection and identifying points where the slope of the beam is zero, which are crucial for ensuring structural stability and functionality.
The first moment-area theorem determines the slope at any point on the beam. This theorem indicates that the change in slope between two points on a beam...
112
Beams with Symmetric Loadings01:15

Beams with Symmetric Loadings

182
The moment-area method is an analytical tool used in structural engineering to determine the slope and deflection of beams under various loads. Consider a cantilever with a concentrated load and moment at the free end. The first step is constructing a free-body diagram to calculate the reactions at the fixed end. Next, the bending moment diagram is plotted to visualize how the bending moment varies along the beam's length, focusing on points where the bending moment equals zero.
The M/EI...
182
Deformation of a Beam under Transverse Loading01:15

Deformation of a Beam under Transverse Loading

252
Understanding beam deflection, particularly for indeterminate beams with overhanging segments and multiple concentrated loads, is crucial for ensuring structural integrity and functionality. The process begins with constructing an accurate free-body diagram, which helps identify the forces and moments acting on the beam. This diagram is vital for visualizing how bending moments vary along the beam's length, influencing its curvature.
The insights from the bending moment diagram extend to...
252
Radiation Pressure: Problem Solving01:09

Radiation Pressure: Problem Solving

330
The radiation pressure applied by an electromagnetic wave on a perfectly absorbing surface equals the energy density of the wave. The wave's momentum also gets transferred to the surface when an electromagnetic wave is entirely absorbed by it. The rate at which momentum is transmitted to an absorbing surface perpendicular to the propagation direction equals the force on the surface.
The average value of the rate of momentum transfer divided by the absorbing area represents the average force...
330
Shear on the Horizontal Face of a Beam Element01:16

Shear on the Horizontal Face of a Beam Element

158
To understand shear on the flat side of a prismatic beam element, consider the vertical and horizontal shearing forces, and the normal forces, acting on the element. The element's upper (U) and lower (L) sections, which are divided by the beam's neutral axis, are examined. The equilibrium of these forces is determined by applying the equilibrium equation, which helps identify the horizontal shearing force. This force is directly related to the bending moments and the cross-section's...
158
Shearing Stresses in a Beam: Problem Solving01:14

Shearing Stresses in a Beam: Problem Solving

168
A cantilever beam with a rectangular cross-section under distributed and point loads experiences shearing stresses. The analysis begins by identifying the loads acting on the beam. Then, the reactions at the beam's fixed end are calculated using equilibrium equations. The vertical reaction is a combination of the distributed and point loads, while the moment reaction is the sum of their moments. The shear force distribution along the beam, resulting from these loads, is established by...
168

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对于动态混合光束弧疗法 (DYMBARC) 的剂量优化.

Chengchen Zhu1, Gian Guyer1, Jenny Bertholet1

  • 1Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland.

Medical physics
|October 26, 2024
PubMed
概括

动态混合束弧疗法 (DYMBARC) 结合非共平面光子和电子弧来改善辐射治疗计划. 与VMAT相比,这种创新技术成功降低了风险器官剂量,提高了个性化癌症护理.

关键词:
剂量测量优化的路径查找.混合光束放射疗法混合光束放射疗法非共平面辐射疗法

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科学领域:

  • 辐射瘤学 辐射瘤学
  • 医学物理 医学物理
  • 癌症治疗方法 癌症治疗方法

背景情况:

  • 结合非共平面和混合光束模式可以提高放射治疗计划的质量.
  • 动态混合光束弧疗法 (DYMBARC) 集成非共平面光子/电子弧,动态门架/聚合器旋转和强度调制.
  • 优化DYMBARC的光束方向是一个复杂的,非凸的挑战,由于广泛的解决方案空间和机器限制.

研究的目的:

  • 建立DYMBARC作为一种可行的放射治疗技术.
  • 通过直接光圈优化 (DAO) 来解决光束路径查找的挑战.
  • 在临床场景中确定光子和电子弧的最佳桌面和门架角度.

主要方法:

  • 生成一个潜在的光束方向的网格,不包括导致碰撞或表干扰的那些.
  • 采用混合DAO算法,将列生成和模拟化相结合,以优化光圈和重量.
  • 将DYMBARC计划与VMAT, colli-DTRT和Arc-MBRT进行比较,使用薄膜测量进行剂量计验证.

主要成果:

  • 与VMAT相比,DYMBARC降低了3.2 Gy (大脑),0.5 Gy (乳房) 和2.9 Gy (骨盆) 的风险器官平均剂量,同时保持了目标覆盖范围.
  • 对目标剂量的电子贡献在DYMBARC的2%至34%,Arc-MBRT的11%至40%.
  • 剂量计验证表明,玛射线通过率超过99.7%.

结论:

  • DYMBARC通过剂量测量优化的路径查找方法成功实施.
  • 该技术有效地结合了非共平面性和混合光束模式,以改进治疗规划.
  • 迪姆巴克 (DYMBARC) 允许对光子和电子贡献进行个性化确定,用于定制的癌症治疗.