Huge inconsistency in disk space measurement, missing 50% of the disk

I own a MacBook Pro 13 Retina, OSX reports disk usage as 450Gb, but utilities such as DiskInventoryX tells a different story reporting 226Gb as used disk space:

How can I convince OSX to give me back my disk space? Given that DiskInventoryX (and other I tested) cannot find where these 411Gb marked as "Other" are what can I do to identify the issue?