Based on our demonstration of a circadian rhythm in the human oral mucosa cell cycle, with most cells in the G(1) phase in the morning and M phase at night, we hypothesized that morning radiotherapy (RT) would lead to less oral mucositis than afternoon RT.

A total of 216 patients were randomized to morning (8-10 AM) vs. afternoon (4-6 PM) RT and stratified by radiation dose, smoking status, and center. Patients receiving primary or postoperative RT alone were eligible. Oral mucositis was scored using the Radiation Therapy Oncology Group (RTOG) criteria and a validated scoring system.

Of 205 evaluable patients, 52.9% vs. 62.4% developed RTOG Grade 3 or greater mucositis after morning vs. afternoon RT, respectively (p = 0.17). Morning RT was also associated with significantly less weight loss after 5 months (p = 0.024). In a subgroup of 111 patients treated to a dose of 66-70 Gy in 33-35 fractions, exploratory analyses revealed a significant reduction in Grade 3 or greater mucositis with morning RT (44.6% vs. 67.3%, p = 0.022) and a longer interval to the development of Grade 3 or greater mucositis (median, >7.9 vs. 5.6 weeks, p = 0.033). In 53 patients, who smoked during therapy, a significant reduction was found in Grade 3 or greater mucositis with morning RT (42.9% vs. 76%, p = 0.025).

In this proof of principle study, morning RT was associated with significantly less weight loss after 5 months and an apparent reduction in oral mucositis in a subset of patients receiving >/=66 Gy and in patients who smoked during therapy.