You can read about this in the next section. The machine used looked a bit like those large mechanical robots that they use to assemble cars. It had a flexible head so it could be positioned in just the right place. After I was fastenned to the bench with the mask the machine was positioned and I got a minute or two of radiation from two different angles. Each session took about fifteen minutes.
More time is spent positioning than radiating.
You don't feel a thing. Having your head held still can be a bit uncomfortable but it doesn't last long. Radiation kills cells. The idea is to kill cancer cells. But it also kills normal cells.