Why are scout views from CT generally not used for planning?

In the context of CT imaging for treatment planning in medical dosimetry, scout views, also known as localization images or survey images, serve as preliminary images to generate a basic layout of the area of interest. However, they are not typically utilized for planning purposes primarily due to the inherent characteristics of beam divergence in CT imaging.

CT scans produce images by rotating around the patient with an x-ray beam that diverges. This divergence occurs in the transverse plane, meaning that as the beam travels through the patient, it spreads out and can create a blurring effect at the boundaries of the imaged area. As a result, the scout views, which are intended to provide a quick overview, do not possess the detailed resolution necessary for accurate treatment planning, especially when precise tumor targeting and organ-at-risk delineation are critical.

The other options, while they may have components of truth, do not fully encapsulate the primary reason for the unsuitability of scout views in planning. For instance, although scout views might not have the same resolution as full diagnostic CT images, this isn't the sole reason they're not used in clinical planning. Similarly, the speed at which images are taken doesn't directly impact the diverging nature of the beam in a way that fundamentally affects