Need to repair Time Machine back-up drive

I have an external back-up for my Time Machine. I think the power went out while it was backing up, and now I can a message that the drive is "read only" or "unavailable." I've tried to fix it using Disk Repair, but I get this message:

Verify and Repair volume “Time Machine Backups”

Checking Journaled HFS Plus volume.

Detected a case-sensitive volume.

Checking extents overflow file.

Checking catalog file.

Missing thread record (id = 129447065)

Missing thread record (id = 129447066)

Invalid node structure

Rebuilding catalog B-tree.

Disk full error

The volume Time Machine Backups could not be repaired.

Volume repair complete.Updating boot support partitions for the volume as required.Error: Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.

Is there anything else I can try before I reformat the disk and start over with my backups? Thanks!