I'd say never because no sane medical professional will be operating or doing any procedure on "some CD from somewhere", pretty much the same with mailing that

I'd say never because no sane medical professional will be operating or doing any procedure on "some CD from somewhere", pretty much the same with mailing that out. They want scans/tests from trusted source to make decisions about person health/life. The only thing they can trust is whatever they have close and used for years. If there is no time to get a new scan/test I think there is no time to download stuff or wait for someone to email things.