If you are dealing with Dicom, is the input shape defined as [batch_size, depth, height, width], [batch_size, channels, height, width] or any other format?
Usually Dicom images are using a single channel, so I assume the channel dimension is missing?
If that’s the case, you would need to create a new conv layer with in_channels=1 or alternatively repeat the input channel 3 times.
Before digging into alternatives, let’s first clarify how you’ve created the input and what each dimension means.