Hi, I want to point out an error:
In the backbone.py following lines

if conv.dim == 2:
self.P1_upsample = Interpolate(scale_factor=2, mode='bilinear')
self.P2_upsample = Interpolate(scale_factor=2, mode='bilinear')
else:
self.P1_upsample = Interpolate(scale_factor=(2, 2, 1), mode='trilinear')
self.P2_upsample = Interpolate(scale_factor=(2, 2, 1), mode='trilinear')

You didn't mention where is the Interpolate from, so maybe you could write it more specifically.

Thank you