Can vitamin a derivative shield immune system during cancer radiation?

This study tests whether adding a drug called ATRA (a form of vitamin A) to standard radiation therapy can prevent a drop in infection-fighting white blood cells in people with a few metastatic tumors. About 58 adults with solid cancers that have spread to up to 5 spots will receive radiation to all visible tumors, with or without ATRA pills taken for 3 days every 3 weeks. The goal is to see if the combination is safe and reduces the risk of low lymphocyte counts, which can weaken the immune system.