Objectives/HypothesisThe purpose of this study was to report the outcomes of a retrospective consecutive cohort study of patients with T1N0M0 glottic carcinoma treated with 4-MV or 6-MV radiotherapy. Study DesignRetrospective case-control study. MethodsThis was a retrospective review of all patients with T1N0M0 glottic carcinoma treated with radiotherapy between January 2000 and December 2012 in the Department of Radiation Oncology at National Cancer Center Singapore. A total of 124 patients were included. Clinical endpoints of interest were: local control (LC), overall survival (OS), and disease-specific survival (DSS). Other prognostic factors for LC were also analyzed: age, gender, smoking status, T substage, dose fraction, field size, anterior commissure involvement, total dose, and overall treatment time. ResultsSix-megavolt photon radiotherapy was used in 73 patients and 4-MV photon radiotherapy in 51 patients. Median follow-up was 4.9 years. The 5-year LC and OS were as follows: 4 MV, 91.6% and 83.4%; 6 MV, 88.8% and 82.8%; and the 5-year LC, OS, and DSS for all patients were 90.4%, 83.3%, and 98.3%. There was no significant difference in LR and OS between 4-MV and 6-MV radiotherapy (P = .92, P = .16, respectively). In the univariate analysis of LC, none of the prognostic factors was statistically significant. Twenty patients (23%) developed second primary cancers, the majority in the lungs. ConclusionsSix-megavolt photon radiotherapy yields comparable results to 4-MV photons. Bolus and computed tomographic simulation are useful to ensure adequate dose coverage of target volume. Follow-up postradiotherapy should incorporate chest imaging, smoking cessation advice, and thyroid function test. Level of Evidence4 Laryngoscope, 127:1061-1067, 2017