Cumulative fetal radiation dose in pregnant oncology patients: Reevaluating risk beyond single-exposure thresholds

Abstract: This systematic review examines how fetal radiation risk is currently understood in pregnant patients undergoing oncologic imaging and treatment, and where that understanding begins to fall short. Clinical decisions are still often framed around single-exposure thresholds, yet real care rarely occurs in isolated steps. We searched PubMed/MEDLINE, PubMed Central, Scopus, Web of Science, and the Cochrane Library for studies published between 2000 and 2025, using predefined eligibility criteria focused on pregnancy, ionizing radiation, and oncology-related exposures. Two reviewers independently screened records, assessed full texts, and extracted data, with disagreements resolved through discussion. Thirty-two studies were included, encompassing clinical observations, dosimetric analyses, and computational modeling. Across these studies, fetal dose estimates varied widely depending on modality, technical factors, and gestational timing. Individual procedures – computed tomography (CT), positron emission tomography/CT, or radiotherapy scatter – often remained below traditional safety thresholds, but a different pattern emerged when exposures were considered sequentially. The cumulative burden, especially when distributed across sensitive developmental windows, appeared less predictable and not fully captured by existing models. Radiobiological responses also shifted with gestational stage, which complicates any attempt to define a universal threshold. The evidence is uneven in places, and much of it relies on modeling rather than direct clinical measurement. Still, a consistent signal appears: risk is not static, and it does not accumulate in a simple linear way. This review brings these elements together and proposes a more integrated perspective. Future work will need to move beyond isolated dose estimates and toward frameworks that reflect how care actually unfolds.