Besides a suction machine, you can get your mouth sprayed everyday by your radiation center to get the gunk, mucus out. The usual rinsing, brushing, drinking water will helps too, and seltzer water rinses, papaya or pineawple juice helps break up the mucus as does other measures to reduce mucus like mucinex, robotusem, and they have yellow and green sponge sticks to get the mucus out from the back area of the mouth if it accumulates there. If swallowing becomes extremity difficult, even by just protein drinks, not compromising breathing, they can put a peg or nasal tube in. I think it's uncommon to stop radiation, chemo yes, and more often due to toxicities, but not as often with radiation, and for everyday of radiation missed is like a 1.7 day loss of survival for each day due to cancer regeneration, and you will have to make the days up, if they can be made up cancer wise. Radiation should be completed through the alloted time, unless unavoidable. There are pain meds, antiinflammatories, others to help you get through this. There can be other reasons for vomiting, nausea, dehydration, constipation, even lying down too soon after eating, raising too quickly. In any case, tell your doctor(s) of your difficulty, and see what they say. Good luck.