From Cellular Radiosensitivity to Precision Radiotherapy: Integrating Functional Assays, Genomics, and Clinical Modeling

Background: Radiotherapy outcomes are determined by the balance between tumor control and normal tissue toxicity, both of which exhibit significant interpatient variability. While radiogenomic and molecular approaches have identified determinants of radiosensitivity, their predictive performance remains limited when used in isolation. Methods: This review provides a comprehensive synthesis of functional assays, genomic biomarkers, and integrative models used to assess radiosensitivity, including radiation-induced lymphocyte apoptosis (RILA), chromosomal radiosensitivity assays, micronucleus formation, γ-H2AX foci kinetics, comet assays, clonogenic survival, and patient-derived organoids, alongside genomic and molecular predictors of tumor response such as hypoxia signatures and gene expression-based models (e.g., RSI and GARD). Results: Functional assays provide direct phenotypic assessment of radiation response, capturing DNA repair capacity, chromosomal stability, apoptosis, and tissue regenerative potential, and have shown associations in several studies with normal tissue toxicity across clinical settings. Tumor radiosensitivity is influenced by intrinsic cellular factors and microenvironmental conditions, including hypoxia and genomic instability. Integrative approaches combining functional, genomic, and clinical data show increasing potential for improving predictive accuracy. Conclusions: Radiosensitivity should be considered a systems-level phenotype requiring multi-dimensional assessment. Conceptual frameworks that integrate tumor and normal tissue responses within a unified modeling approach, supported by measurable biological and clinical parameters, represent a promising direction for clinically actionable precision radiotherapy. The integration of functional assays with genomic and clinical modeling frameworks represents a promising strategy for advancing personalized radiotherapy and improving therapeutic outcomes.