There have been several improvements on the MC algorithm, such as that described in the paper "A Surface Smoothing Method for a 3D Model of a Medical Object", however, many current free software still employ the MC algorithm to create triangular meshes, such as 3D-slicer

https://link.springer.com/content/pdf/10.1007/978-3-642-34197-7_19.pdf

https://www.slicer.org/

I assume by "DICOM" you mean 3D grayscale image in DICOM format. In some cases extracting isosurface by marching cubes directly from the grayscale image produces usable results, but most often segmentation is not that trivial. In the last 30 years, many manual, semi-automatic, and automatic segmentation methods have been implemented - Google Scholar has more than 200,000 hits for the search terms +medical +"image segmentation".

As Edgar above suggested, you can try 3D Slicer's segmentation methods. Recent nightly versions have a very powerful segmentation module (Segment Editor), which contains a number of segmentation tools (and you can get a couple of more by installing SegmentEditorExtraEffects and other extensions from the Slicer appstore).