Carcinoma/radiotherapy; Ethmoid Sinus/radiation effects; Frontal Sinus/radiation effects; Mucocele/etiology; Nasopharyngeal Neoplasms/radiotherapy; Neoplasm Recurrence, Local/radiotherapy; Radiation Injuries/etiology; Sphenoid Sinus/radiation effects; Adult; Combined Modality Therapy; Diplopia/etiology; Endoscopy; Female; Headache/etiology; Humans; Magnetic Resonance Imaging; Middle Aged; Mucocele/diagnosis; Mucocele/diagnostic imaging; Mucocele/pathology; Mucocele/surgery; Nasal Obstruction/etiology; Neoplasm Recurrence, Local/complications; Neoplasm Recurrence, Local/drug therapy; Radiation Injuries/diagnosis; Radiation Injuries/diagnostic imaging; Radiation Injuries/pathology; Radiation Injuries/surgery; Sphenoid Sinus/pathology; Sphenoid Sinus/surgery; Time Factors; Tomography, X-Ray Computed