bwtraceboundary draws outside object, whereas edge identifies "last pixels" of object, right?

Reading the documentation, am I correct in understanding that bwtraceboundary draws outside the object whereas edge identifies the "last pixels", the "end" of the object itself?

It is important that I use (e.g. image) only the object itself, and not accidentally "expand" the object larger than it is, which it seems bwtraceboundary would do, that I should therefore use edge.

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The context for this question:

I'm learning to work with DICOM structure sets and dose files with ulrikls's code:

dicomrt2matlab('file')
load('resultingfile.mat')
imshow(contours(9).Segmentation(:,:,75)) % to show the 75th slice of contour
end

An intermediate goal is to image the RT-Image and RT-Dose with the outline of an RT Structure Set structure. I suppose this work has already been done and that I should search MathWorks Support ...

Edit: I will try Jun Li's "Dicom Operator - EsmeProcess" to see how he's implemented DICOM 3D viewing.