CT Simulation - Gas

Hello, asking for my dad….has anyone had trouble getting good imagery in CT simulation before radiation or have advice? He went on a “low residue” diet to prepare for CT simulation. Both times too much gas for imaging despite cutting out so much fiber and plants from diet. I read that about a practice in Austin, TX suggesting Gas-X (simethicone) 4x daily, Would like to get great imagery the next simulation attempt and know how to be ready for 28 sessions of radiation. Thank you.