I thought the photon beam was for smaller, direct application to cancer/tumor. For instance, I had a .2 psa, then several weeks later a .3 psa (Post prostatectomy from 2013) . Did PET scan, but Radiation Oncologist advised there's about a 40% chance he will see it when psa is still .3, thus have to treat larger areas if the goal is curability. That's all I understand... not much.