The prognostic impact of daytime and seasonality of radiotherapy on head and neck cancer

Highlights: • Circadian rhythm was previously shown to correlate with treatment toxicity. • This is the first study investigating the impact of seasons on oncologic outcome. • Radiotherapy delivery in the darker half of the year yields better tumor control. The potential impact of daytime and season of radiotherapy application on prognosis is unclear. This was analyzed in a retrospective cohort of patients who were diagnosed with non-metastatic head and neck squamous cell carcinoma (HNSCC) and treated with definitive radiotherapy with or without chemotherapy.