- Arm I: Patients receive radical radiotherapy once daily, 5 days a week, for 4-6.4 weeks. Patients also receive oral niacinamide once daily 1.5-2 hours before initiation of each radiotherapy dose and carbogen through a closed breathing system (face mask with a tight air seal or a mouthpiece with nasal clip) once daily beginning 5 minutes before initiation and continuing until completion of each radiotherapy dose.