PURPOSE: To examine the feasibility of the treatment planning for minimizing carotid artery dose in the radiotherapy of early glottic cancer. MATERIALS AND METHODS: From 2007 to 2010, computed tomography simulation images of 31 patients treated by radiotherapy for early glottic cancer were analyzed. The virtual planning was used to compare the parallel-opposing fields (POF) with the modified oblique fields (MOF) placed at angles to exclude the ipsilateral carotid arteries. Planning target volume (PTV), irradiated volume, carotid artery, and spinal cord were analyzed at a mean dose, V35, V40, V50 and with a percent dose-volume. RESULTS: The beam angles were arranged 25 degrees anteriorly in 23 patients and 30 degrees anteriorly in 8 patients. The percent dose-volume of PTV shows no statistical difference. Conversely, the cumulative percent dose-volume of carotid artery shows the significant difference (p<0.001). The mean doses of carotid artery were 38.5 Gy for POF and 26.3 Gy for MOF and the difference was statistically significant (p=0.012). Similarly, V35, V40, and V50 also showed significant differences between POF and MOF. CONCLUSION: The modified oblique field was respected to prevent a carotid artery stenosis and reduce the incidence of a stroke based on these results.