After radiotherapy for cancer, my brother developed a bald spot on his head, which persisted for 15 years. A couple of months after he began daily niacin, his bald spot had grown back. The radiation had also caused a vision problem in the eye on the radiated side, resulting in a loss of 40% of the visual field in that eye. After a few months on niacin, the vision in that eye was almost normal.
My dad has a small open wound in his mouth from radiation for salivary gland cancer. The last treatment was 2 years or so ago. I wonder if the niacin might be effective for that. He’s 93 and still pretty active.