I recommend expanding foam ear plugs, the kind you roll into a tighter-than-normal size and insert into the ear canal. Then wear quality ear muffs over that. I don't know the total reduction in db lever, but it significantly less then either by themselves.
Sorry to hear you have to undergo chemo. My infusions 5 years ago were with Keytruda, which triggers your immune system to attack the cancer. Hang in there, and if you need support or have to rant, we're here for you.