Problem with loading data to rcnn model

Hi, I am trying to train rcnn model, but I have few problems when I am using batch_size>1.
My function which make dataset returns a single img tensor and a single target (dictionary):

        return (

Later I am loading datasets to dataloader which loads data to the training process.

   with tqdm(train_loader) as _tqdm:
        for x, y in _tqdm:
            x =
            for key, value in y.items():
                y[key] = torch.tensor(value).to(device)

            outputs = model(x, y)

When batch_size is f.e. == 2, then x is a list of two tensors of shape [D, H, W] but y is a dict where every key have two values. Then occurs error:

.../", line 64, in forward boxes = target["boxes"] TypeError: string indices must be integers
So I assumed that probably it can’t handle with dictionaries and I pass:

output(x, [y])

Then error changes to:

.../", line 99, in forward
target_index = targets[i] if targets is not None else None
IndexError: list index out of range

Any ideas how to make it run properly?