Comfortable or safe? I was somewhat confounded after my neck dissection to discover that the trip to my gym suddenly had a "breakneck curve" I had never noticed before. Two years later and it's back to being a mild bend in the road.
So while I could drive safely, I had to twist my entire body and turn my head around so far that it was painful, not comfortable for about four months. After my neck dissection, I did not drive to my radiation treatments after my cancer had come back as it required a high speed merge that I could not do fast enough to be safe. But I also had had salvage surgery which traumatized my shoulder and chest muscles at the same time so that was an additional factor that makes it hard for me to accurately sort out the impact of the neck dissection.

I drove myself the first two weeks to radiation the first time I had cancer but I had not had a neck dissection. By the third week, the Erbitux had made the raw skin on my neck to painful to drive safely.

So IMO, it depends on how challenging your drive to radiation is as to when you can safely do it.
Keep the faith
Charm