Influence of external beam irradiation technique on early change of brainstem auditory evoked potential in nasopharyngeal carcinoma patients

Objective: To investigate the influence of different external beam irradiation techniques on early change of brainstem auditory evoked potential (BAEP) in nasopharyngeal carcinoma (NPC). Methods: Ninety-seven NPC patients treated with external beam irradiation were monitered through BAEP far 6 times before, within (36-40 Gy/3-4w), right after, three, six, and twelve months after radiotherapy. Of them, fifty-six patients were treated with conventional radiotherapeutic technique (fixed source-skin-distance) and 41 with the improved technique (cerrobend block facio-cervical portal and isocenter). The relationship between the different radiotherapeutic technique, change of BAEP, age of patient, clinical T-stage and accompanying diseases, such as diabetes, hypertensive disease and coronary heart disease, were analyzed. Results The abnormal rate of BAEP was 61.9% twelve months after radiotherapy. The abnormality rate of BAEP within the period of radiotherapy (36-40 Gy/3-4w), right after, three, six and twelve months after radiotherapy was 14.4%, 25.8%, 27.8%, 37.1%, and 61.9%, respectively. Twelve months after conventional technique treatment, the abnormality rate of BAEP and brain stem auditory pathway were 71.4% and 30.4%, compared with 48.8% and 12.2% treated with the improved technique (χ2=5.15, P < 0.05 and χ2=4.45, P < 0.05). The abnormal rate of BAEP 12 months after radiotherapy was significantly higher in patients older than 50 years, so were patients with parapharyngeal region and/or skull base invasion, high T stage, and with complications, such as diabetes, coronay atherosclerotic heart discus (CHD), and hypertensive disease. Conclusions: The change of brainstem auditory evoked patential in NPC patients treated with radiotherapy is related to patient's age, accompanying disease and clinical stage. The improvement of irradiation technique may result in the reduction of abnormal rate of BAEP and the brain stem auditory pathway. (authors)