Well, thanks a lot, that did the trick.
I had to set the cropsize to 5 and not 10 though. Otherwise the resulting image is somehow 10 pixels wider. It seems contre-intuitive when I read the comments from the page you linked.
The code bellow works for me.
// add black border to prevent leakage
// first shrink the image
using CropImageFilterType = itk::CropImageFilter <Image3d, Image3d>;
CropImageFilterType::Pointer cropFilter = CropImageFilterType::New();
cropFilter->SetInput(v_CropedImg);
Image3d::SizeType cropSize;
cropSize.Fill(5);
cropFilter->SetBoundaryCropSize(cropSize);// then expand with black borders
using ConstantPadImageFilterType = itk::ConstantPadImageFilter <Image3d, Image3d>;
ConstantPadImageFilterType::Pointer padFilter = ConstantPadImageFilterType::New();
Image3d::SizeType v_ExtendRegion;
v_ExtendRegion.Fill(5);
padFilter->SetInput(cropFilter->GetOutput());
padFilter->SetPadLowerBound(v_ExtendRegion);
padFilter->SetPadUpperBound(v_ExtendRegion);
padFilter->SetConstant(-3000);
padFilter->Update();
return padFilter->GetOutput();