The most important issue here is that you complete treatment. If you have 35 scheduled radiation visits, then you must complete all 35. It is a sequential treatment but missing a day or two shouldn't make a difference. Patients not completing the treatment protocol have poorer survival odds in general.

The machines are VERY busy and often are run for 2 shifts every day at many treatment centers, one can only imagine the logistical nightmare if too many patients were rescheduling. A day or 2 of downtime can really mess up their schedules as well. When I worked for Siemens we scheduled all maintenance, repairs and upgrades after hours and on weekends, unless the machine was inoperable or in a dangerous condition.

I want to make clear this applies mainly to the frontline treatment, i.e. radiation. Chemo is given as an adjunct and sometimes chemo protocols are changed or shortened without adverse effects or conversely, due to adverse effects.