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.