title: Comparison between 4-MV and 6-MV radiotherapy in T1N0 glottic cancer.
abstract: OBJECTIVE
  The 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.
  
  
  METHODS
  Retrospective case-control study.
  
  
  METHODS
  This 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.
  
  
  RESULTS
  Six-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.
  
  
  CONCLUSIONS
  Six-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.
  
  
  METHODS
  4 Laryngoscope, 127:1061-1067, 2017.
authors.affiliation: Department of Radiation Oncology, National Cancer Center Singapore, Singapore.
authors.forename: Kiattisa
authors.initials: K
authors.lastname: Sommat
authors.affiliation: Department of Radiation Oncology, National Cancer Center Singapore, Singapore.
authors.forename: Nelson Ling Fung
authors.initials: NL
authors.lastname: Yit
authors.affiliation: Department of Clinical Trials and Epidemiology, National Cancer Center Singapore, Singapore.
authors.forename: Li-Lian
authors.initials: LL
authors.lastname: Kwok
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D005260:Female; D005500:Follow-Up Studies; D005931:Glottis / Q000473:pathology*; D006801:Humans; D007822:Laryngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D060787:Neoplasm Grading; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000379:methods*; D012189:Retrospective Studies; D012846:Singapore; D016896:Treatment Outcome
keywords: Radiotherapy; glottic cancer; larynx