A systematic literature review of the potential relationship between tumour response and the timing of radiation therapy

This systematic review aims to examine the previously published studies on the application of radiotherapy (RT) and determine the possible benefits of incorporating a circadian-based time-of-day RT concept to improve outcomes. A literature search was conducted to identify relevant studies published between 2008 and 2024 using PubMed, Science Direct and Google Scholar databases. This systematic review included studies that analysed outcomes of patients with cancer who underwent RT in relation to the time of the day for those treatments. Nineteen studies were included in the systematic review; fourteen were retrospective, and five were prospective randomized trials. This review revealed that 64.3% (9/14) studies measured overall survival (OS) and tumour control, 14.3% (2/14) studies measured clinical outcomes and treatment toxicity, and 21.4% (3/14) retrospective studies measured Chrono-RT-induced toxicity only; however, they do not have consistent results. In addition, 100% (5/5) prospective studies measured treatment toxicity effects only whether patients were treated in the morning or evening. Existing literature suggests that Chrono-RT may reduce adverse symptoms in highly proliferative tissues and improve clinical outcomes. However, further examination of the Chrono-RT concept, in well-designed prospective trials and retrospective studies, is warranted to validate this hypothesis and for consistent results.