I’ve recently finished radiotherapy and understand your concerns.
I was told to be fully hydrated before leaving home for RT. That was 3 mugs of green tea and an empty bladder, before I left for 1hr journey to the hospital. On arrival, min. ½ hour before RT time, report in, empty bladder, then drink 3 cups of water and wait to be called.
On a good day this worked fine, but as the radiologists told me, sometimes doesn’t because of uncontrollable reasons such as weather temperature, humidity, the body, longer journey or waiting time, etc.
I frequently had to fill or part-empty my bladder and once empty my bowels when the side effects of RT kicked in with wind and diarrhoea. This was the same for other patients.
All the radiologists who treated me were absolutely brilliant about this thankfully. You can only do your best.
I think the problem is the radiologist’s bad bedside manner. As you said they went ahead with treatment.
It might be worth speaking to someone in the department, a nursing sister, about your concerns, for your peace of mind, which is important.