30 grays over 30 days is quite doable. My husband had 70 grays over 35 days the first time, and then 20 grays over 5 days twice. The first time he had multiple side effects, the remaining two times were not bad at all although he was getting more grays per day (20 divided by 5= 4 grays a day). Has your dad had his teeth checked and fluoride trays made? That should be done prior to radiation starting. Keep records of his daily intake, get him a Waterpik so he can rinse the gunk out of his mouth (use it on the lowest setting with the tongue scraper attachment and with a bit of magic mouthwash thrown in), put a humidifier in his bedroom and maybe set up a station with things he might need in the sitting room. He’ll get through it and you will too. Wishing you two all the very best.