Seat belt attachment for chest injuries

  My sister had breast cancer about 6 years ago and she had issues with using the seat belt, since she had radiation and chemo treatments. Sadly, like most radiation treatments, you have raw and very painful wounds. Sometimes she didn't wear her seat belt and other times she put the strap behind her back, which is terribly unsafe and can also get her a ticket. Anyhow, I was thinking there should be a attachment or some sort of seat belt created for people with chest injuries. It's painful enough to go through what they are suffering, but it would be great if someone created a safe ergonomically seat belt attachment for this case. I just know it's not safe to put the strap behind your back, but I am thinking there are probably other positions the strap could fall and still keep you secure if you were in an accident.