Inhomogeneous Treatment Planning
KeywordsUnit Density High Density Region Lung Density Inhomogeneous Region High Density Material
In and beyond low density regions, such as lung, the decrease in attenuation causes an elevation of the absorbed dose.
Within low density regions the decrease in scattering partially offsets the elevation in dose.
The magnitude of the actual dose in and beyond low density regions, relative to that on a unit density basis, depends in a non-linear manner on the location, extent, and density of the inhomogeneous region.
For inhomogeneities as large as some dimensions of the lung, the geometric decrease in intensity becomes appreciable. Consequently, in the extension or contraction of dose contours a geometric correction is necessary.
Beyond high density regions, such as bone, the increased attenuation produces a contraction in the dose contours with a consequently decreased dose.
Within high atomic number material, such as bone, and immediately beyond in the interface region, there is an elevated dose due to enhanced scattering.
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