Peritumoral volume segmentation

I want to delineate peritumoral volume using my 3D-slicer.

The segmentation of tumor has been conducted along the boundary of pulmonary nodules (the gray area in the picture). Now I wonder whether the volume can be dilated 10 mm (or 20mm) (the blue area in the picture) in three dimensions uniformly based on the tumor boundary? And then I intend to save tumor volume and peritumoral volume respectively.

Yes, you can use Margin effect to dilate a segment by a margin. You probably want to make a copy of the GTV before you grow it, and set Masking/Modify other segments to “Allow overlap” to allow the GTV and PTV segments to overlap.

If you want to restrict margin growing to be inside the lungs, you can segment the lungs using Lung CT segmenter module (provided by LungCTAnalyzer extension), import the lung segment into your segmentation, and choose it as Editable area in Masking section when you use the Margin effect.

I could not find Margin effect and LungCTAnalyzer extension in my 3D slicer (version 4.10.2). should I update a latest version?

Yes, you always need to use the latest stable or latest preview release.