When do you give treatment breaks for patients with NSCLC undergoing chemoradiation with serious toxicity?

I agree with @Dr. First Last's approach. I am very aggressive in not introducing treatment breaks during radiotherapy. One approach that I occasionally use to "make up" for dose issues when a break is inevitable is to accelerate at the end of treatment to make up for the break rather than to specifically dose increase. In other words, I will do continuous treatment through weekends towards the end of the course for breaks that happen earlier

For esophagitis, I try to keep the patient going with oral or IV supplementation and analgesics. But I have been giving a short break for neutropenia less than 500. I resume as soon as I see a steep recovery so it is rarely more than a few days. If the normal tissue constraints have not been exceeded than I have added 2-6 Gy if there is more than a 2-3 day break in treatment.