I have never heard of using cornstarch, but there are many things I haven't heard of. I was treated at UCSF Comprehensive Cancer Center and I was told to have nothing on my skin prior to radiation therapy to avoid any bolus (enhancing) effect. I was told to apply anything for the skin afterwards. They make special gels for the purpose, I think it's called Radia Care. As your skin gets dried out, the itching is something to avoid. Why they would recommend something to dry your skin out further is beyond me. They also gave me a steroid cream towards the end of treatment.