A 16-year-old boy presents with recurrent epistaxis and nasal obstruction for 6 months. Nasal endoscopy reveals a highly vascular mass in the nasopharynx. CT shows a lobulated mass with bowing of the posterior maxillary wall and widening of the pterygopalatine fossa. Biopsy confirms nasopharyngeal angiofibroma. What is the drug of choice for preoperative embolization to reduce intraoperative bleeding?