Low-dose ionizing radiation exposure and tumor risk: An umbrella review of systematic reviews and meta-analyses.

Low-dose ionizing radiation (LDIR) arises from medical, occupational, and environmental sources, but cancer risks at low doses remain debated. We conducted an umbrella review of systematic reviews and meta-analyses on low-dose-relevant ionizing radiation exposure and observed tumor occurrence. We searched MEDLINE, Embase, PubMed, Scopus, ScienceDirect, Web of Science, and Epistemonikos for publications through July 2026. Findings were synthesized descriptively by exposure context and cancer type. We assessed methodological quality using AMSTAR 2, classified temporal exposure patterns and dose applicability, evaluated primary-study overlap, and rated certainty using an overview-level GRADE approach. Forty reviews were included: 15 systematic reviews without meta-analysis, 15 systematic reviews with meta-analysis, and 10 meta-analyses. Leukemia-incidence findings following pediatric computed tomography and protracted low-dose-relevant radiation exposure were rated as moderate certainty. Evidence for residential proximity to nuclear facilities, aviation exposure, occupational thyroid cancer, adult central nervous system tumors, dental X-ray-related meningioma, and skin cancer was less certain. No additional pooling was performed because reviews addressed heterogeneous questions and shared primary studies. These findings support exposure-specific, certainty-informed interpretation rather than a uniform conclusion across radiation exposure settings.