 Local only at the painful joint low dose irradiation of the chronic patients results in most patients in a significantly reduced pain, not only direct after the therapy, but also lasting for more than 12 month in many cases. The patients experience enhanced mobility and increased quality of life. The molecular and cellular processes leading to the pain reduction are just fragmentarily analyzed. Our group revealed that macrophages are key players in radiation-induced immune modulation. Inflammatory macrophages exposed to low doses of radiation showed a reduced inflammatory capacity and attenuated an inflammatory microenvironment. Besides macrophages further immune cells are most likely involved in reduction of inflammation following LD-RT, as in vitro already shown for neutrophils. 