With proton’s Bragg-Peak characteristics (look it up), exposure to surrounding normal tissues is minimized, with little radiation entry-dose, minimal radiation scatter, and no radiation exit-dose. Side-effects like burns to the skin would be rare.

@gently
Yes I did get what they called a sunburn type of burn on each hip. I was told this would occur as the is where the proton beam enters body. Even though the proton beam releases it's energy where it is programmed some radiation does occur when entering body.

I did not notice it until one day my wife said she could see the sunburn on both sides of my hip. It got more pronounce over time. Then when treatments ended it turned into a tan color. I still had it months after treatment ended and asked my oncologist/radiologist about it.

He said completely normal reaction of skin and would slowly fade each month after treatments. And it did. It did not hurt or bother me so I did not mention it as a side affect.