Scientific and Clinical Studies on Variation in Individual Response to Ionising Radiation: A Scoping Review.

Ionising radiation, defined as radiation with sufficient energy to remove electrons from atoms and molecules, can produce significant biological effects in living tissue. Individual response to ionising radiation varies considerably and underpins both deterministic tissue reactions and stochastic effects such as cancer. The concepts of radiosensitivity and radiosusceptibility are central to this variability; however, their definitions and applications remain inconsistent across the literature. This scoping review aims to systematically map and analyse how radiosensitivity and radiosusceptibility are defined, applied, and distinguished in scientific and clinical studies of ionising radiation. The review was conducted in accordance with the Arksey and O'Malley framework and reported using PRISMA-ScR guidelines. A comprehensive search of PubMed and Scopus (December 2025) was performed using a broad Boolean strategy to capture variation in terminology. Following staged filtering and duplicate removal, studies were screened at title/abstract and full-text levels by two independent reviewers using predefined inclusion and exclusion criteria. Data were extracted using a standardised framework and synthesised descriptively. The search yielded over 14,000 records, which were systematically reduced through structured filtering to a manageable dataset for screening. The final included studies demonstrated substantial heterogeneity in study design, endpoints, and terminology. Radiosensitivity was predominantly characterised using cellular and molecular measures, including DNA damage, repair capacity, and cytogenetic assays, whereas radiosusceptibility was particularly associated with normal tissue toxicity and radiation-induced cancer risk. The term "radiosusceptibility" was comparatively underrepresented. Across studies, considerable inter-individual variability in radiation response was consistently observed. This review highlights a lack of conceptual clarity and consistency in the use of radiosensitivity and radiosusceptibility. Greater definitional precision and methodological alignment are needed to improve comparability across studies and support the integration of biological and clinical evidence, with implications for personalised radiotherapy and radiation risk assessment.