DICOM RTSTRUCT changed after segment editor

Operating system:windows 10
Slicer version:4.10.2
Expected behavior:export dicom RTSTRUCT correctly
Actual behavior:
First I loaded Dicom with RTSTRUCT, then I just wanted to modify one segment a little bit using segment editor. It is requested to convert contour into labelmap. After modification, I exported it to another Dicom subject with new study. However, when I opened the new one, the RTSTRUCT was changed. Some of contour having triangle and some of segments were combined as one. I was very frustrated. Does any one can help me?

This is the expected behavior. RT structure set is very poor 3D representation, as it is highly anisotropic (contains high-resolution contours within a slice, and there is no information about contour shape between two slices).

Segment Editor module performs all editing in 3D labelmap at the chosen resolution. If you find that the default resolution is not sufficient to represent all relevant details then use higher resolution. A simple way of achieving that is by creating the binary labelmap representation using an “oversampling factor” larger than 1.0 (e.g., 1.5-2.0).

Instead of just changing oversampling factor, you can specify custom resolution and extents using “Specify geometry” button in Segment Editor module.

You did two things that changed the segmentation.

  1. Change the master representation from planar contours (the original inefficient representation) to binary labelmap
  2. Export it using a different CT image

I would suggest increasing the resolution of the master volume. In Segmentations module if you long-click Create… in the row of Binary labelmap, choose the CT you will export it with (addresses #2), then click Set geometry and specify an oversampling of 2 (addresses #1).

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Oh, and please use a recent Preview version because 4.10.2 is almost two years old and one thing that improved significantly is the segmentation infrastructure.

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Is there any way to edit contour directly instead of converting them to labelmap then converting back to dicom RT structure again?

Slicer only supports true, direct 3D editing. Parallel contours are very poor representation of segmentations, so I would not recommend to use them at all and if you need DICOM export then switch to DICOM segmentation object instead.

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