The main purpose of a physician extender (in a way, anyone in a rad onc practice who does what an MD "technically" could - check vitals, answer phones, record billing codes, schedule patients, treat patients, contour, calc dose, write notes, field questions, send out prescriptions, file appeals, see followups, etc) is to let the MD practice at the top of their skillset doing only those thing that legally require a medical license to do.
Even with a little slack in my schedule, it can save me money for anyone lower paid to do something that I "technically" could, even if they aren't totally awesome at it. That is the essence of specialization.
In the one place I practiced where we were fully staffed at every level including scribes and a PA, not only was productivity sky high, but I believe everyone (including patients) was happier and more fulfilled. We all got to practice at the top of our game. We had a very cohesive dept and very little turnover.
Since I didn't see a lot of simple breast or prostate patients, I didn't utilize our PA that much, but my partners did. For me, with complex cases and lots of reirradiation, the scribe was a much better value. Although having a scribe or scribe/MA costs money, they allowed me to see an extra 1-2 consults per day and improved my job satisfaction and on-time departure more than any other person in the dept. They more than made up their "cost."