TD12-Scatter Analysis and Tissue Inhomogeneity Correction

Cheng B. Saw, PhD

UPMC Cancer Centers, Pittsburgh, PA  15232

This presentation will examine scatter analysis and tissue inhomogeneities. 

In its simplest form, the dose to a point in a phantom can be separated into two components referred to as the primary and scattered components.  The primary component comes directly from the target and is influenced by factors in the treatment head such as collimator settings.  The scattered component is from the beam interacting with the patient phantom.  The scattered components are determined based on the Clarkson’s method.

The presence of inhomogeneities such as bone and air changes the dose distributions.  The effect of tissue inhomogeneity can be broadly classified as the changes in the absorption of primary beam, the scatter of photons, and secondary electron fluence.  The relative importance of these effects depends on the region of interest.  For regions lying beyond the inhomogeneities, the predominant effect is attenuation of the primary beam.  Scattered electron fluence contributes strongly to the dose within the inhomogeneity tissues and at boundaries.  Scattered photons strongly contribute to the dose distributions near the inhomogeneities than farther away.

TD12 - 散射线分析和组织不均匀性校正

Cheng B. Saw, PhD

UPMC Cancer Centers, Pittsburgh, PA  15232

本讲讲述散射线分析和组织不均匀性校正。

模体中一点的剂量可以分为两部分：原射线和散射线。原射线来自X射线靶，受到治疗机机头（如准直器设置）的影响；散射线源于射线与模体的相互作用，可以用Clarkson方法计算。

不均匀组织（如骨和空气）的存在会改变剂量分布。组织不均匀性的影响大体可分为原射线吸收、光子散射及次级电子注量的变化。各种影响的相对重要性取决于感兴趣区的位置。处于不均匀组织后面的区域，主要受到原射线衰减变化的影响；在不均匀组织内和边界处，主要受到散射电子注量变化的影响；散射光子对不均匀组织附近区域的剂量分布影响大。