Impairment of optic path due to radiotherapy for nasopharyngeal carcinoma

Purpose: To evaluate the impairment of optic path caused by radiotherapy for nasopharyngeal carcinoma (NPC). Methods: Visual evoked potential was used to evaluate the functional impairment of optic path by an 8 MV linear accelerator or (CO)-C-60 gamma-ray radiotherapy in 63 (23 women and 40 men) patients with nasopharyngeal carcinoma before radiotherapy, at the end of radiotherapy, 6 months and 1, 2 and 3 years after their radiotherapy respectively. Results: In the female group, the latency of VEP elicited by the three types of elements significantly delayed 2 and 3 years after radiotherapy than that before radiotherapy, at the end of radiotherapy, 6 months and I year after radiotherapy; there were no significant difference among VEP amplitudes elicited by the three types of elements before and after radiotherapy. In the male group, the latency of VEP elicited by the medium and the small elements significantly delayed I year after radiotherapy than that before radiotherapy and at the end of radiotherapy, the VEP latency elicited by the small elements was significantly prolonged 3 years after radiotherapy compared to that just after radiotherapy, while the VEP amplitude elicited by the large elements was significantly attenuated I year after radiotherapy compared to those before and just after radiotherapy. Conclusions: In the female group, the significant prolongation of VEP latency happened at the end of radiotherapy and lasted for 3 years, while the VEP amplitude did not change significantly during the 3 years after radiotherapy. It indicates that the sustained impairment by radiation within the female visual nerve system starts at the end of radiotherapy, but the impairment was mild. In the male group, the significant prolongation of VEP latency mostly happened I or 2 years after radiotherapy. It was shown that the radiotherapy for nasopharyngeal carcinoma certainly injured the optic path, and there was difference in the impairment between the two sexes.