The standard radiation therapy is 50Gy in 25 treatments using 6megavoltage photons, for larger ladies a mix of 6/18Mv May be used as 18mv is more penetrating. There is a new protocol from Canada which is 42.6Gy in 16 treatments (this is usually for smaller younger women). For ladies under 65 a “boost” to the lumpectomy site is used either 5 treatments (after the 25) or 4 (after the 16), this uses electrons which do not penetrate very deeply, the energy depends on the depth of site (usually 6mev or 9mev). Mastectomy patients are 50Gy in 25 treatments this is usually with electrons but may also be photons. Care is taken to
minimise dose to lungs, ribs, heart and liver - each plan is customised to your body using the CT scan done at your planning session.
I hope that helps :)