Dad starts radiation therapy tomorrow what should he know?

Found my way here to be a help to my dad- he is 81 and was recently diagnosed with stage 4 lung cancer. He and my mother aren’t the most tech-savvy of folks so I decided joining a few support groups could be my way of supporting this fight! So, with that said, he starts radiation tomorrow, and if you had one thing you wish someone had told you before you started (or your loved one started) what would that be? Just trying to help prepare mom for any side-effects that could potentially appear. Thanks in advance for sharing the wisdom you’ve gained on your own heroic journey xoxoxox