Radiotherapy treatment time delay evidence, part I: Update on cervical, anal, prostate, and head and neck cancers.

Treatment delays during radiotherapy for head and neck cancer (HNC) are a well-established factor negatively affecting clinical outcomes, with similar trends observed in other cancers. In this first part of a two-part review, we assessed the impact of overall treatment time (OTT) prolongation on locoregional control (LRC) and survival (SV) in cervical cancer (CC), prostate cancer (PC), and anal cancer (AC), while updating evidence for HNC. A comprehensive literature search was performed in evidence-based databases, including MEDLINE, identifying studies evaluating the relationship between OTT prolongation and outcomes. Particular attention was paid to the strength of evidence, distinguishing univariate analysis from multivariate analysis (MV-An). For CC, 37 articles were identified, with 88.8% reporting a detrimental impact on LRC and/or SV, mostly supported by MV-An. In AC, 15 studies were found, with 33.3% showing negative impacts, although with weaker evidence. For PC, 12 articles were reviewed, with 66.6% demonstrating detrimental effects mainly on LRC or biochemical control, and occasional associations with cancer-specific SV. Recent studies in HNC reinforced prior findings. When available, radiobiological parameters and practical recommendations are provided. In conclusion, strong evidence confirms that prolonged OTT worsens outcomes in HNC and CC, with less consistent but relevant effects in PC and AC.