Bens, I mis-spoke, I'm not using the Elekta Unity Machine, I'm using a Linear Accelerator True Beam with Hypersight by Varian Medical Systems, sorry for the mix up. As far as the margins go, the short answer is 5mm. When I asked my Dr. he proceeded with diagrams and talked for 10 minutes about past experiences and why they use that, I only wish I could remember everything he said, sometimes he just overwhelms you with info.