Gamma radiation treatment

I have apatient with Knee pain/swelling (OA and ?goput on XRAy) who just had injections of gamma radiation in his knee. This relkieved his pain and the swelling has reduced (he was having 100ml fluid aspirated easch week). Can anyone tell me more about the gamma radaition treatment, or direct me to info? I am treating this patioent with exercises.stretches to restore his ROM/strength. I have steerd clear of EPA as I wasn't sure about its effects with the radaition treatment.