This systematic review compared incidence of moyamoya syndrome after receiving photon or proton cranial radiation for pediatric brain tumors. The authors found that the incidence of moyamoya syndrome after receiving proton radiation is almost double that of photon-induced moyamoya syndrome. Patients who received PBT for the management of pediatric brain tumors are more likely to develop moyamoya syndrome at the age of less than 5 years. Most patients with proton-induced moyamoya are more likely to be diagnosed within the first 2 years after the completion of their proton beam therapy.