Sturge-Weber syndrome (SWS) is a rare congenital disorder with diverse manifestations, including diffuse choroidal hemangiomas causing visual impairment. This case report describes a 14-year-old girl with retinal detachment due to diffuse choroidal hemangioma, treated effectively using external beam radiation therapy (EBRT). The treatment achieved a significant 55% reduction in choroidal thickness after the first phase and near-complete remission after supplementary therapy. This case underscores EBRT's efficacy and highlights the potential of adaptive radiation strategies for managing complex SWS-related ocular complications. Early intervention remains crucial for optimizing patient outcomes.