This paper reviews efforts on using high energy (25-30 MeV) and high power (10-20 kW) electrons linacs and lower energy (7MeV) photon linacs, PET (Positron Emission Tomography) radioisotope are producted through photonuclear reactions such as F (y,n) F, which also allow production of other PET radionuclides C, N, and O. Other mostly used medical radio nucleus Tc can also be obtained by using the electron linacs, through photofission or photo nuclear reactions. Proton linacs for PET have also been recently developed and the product has been available in the market since 2005. The linacs have been tested for F production. As a proton accelator, the target system and nuclear reactions are similar to the ones used in PET cyclotrons.