Dose to the Fetus in Pregnant Women Undergoing Stereotactic Radiosurgery for Brain Tumors

Objectives: Stereotactic radiosurgery (SRS) treats intracranial tumors during pregnancy when intervention cannot be delayed until delivery. However, fetal radiation exposure raises toxicity and carcinogenic concerns, especially above 50 mGy. This review evaluates published evidence on fetal exposure during SRS to assess the safety of Gamma Knife radiosurgery (GKRS) compared with other platforms. Although pregnancy is a relative contraindication to radiation therapy, urgent intracranial tumor treatment may be necessary, making knowledge of fetal exposure and safety critical. Methods: A comprehensive literature search (PubMed, MEDLINE, Embase, Google Scholar) identified studies published through May 2026 evaluating fetal radiation doses, exposure determinants, dosimetric methodologies, and maternal-fetal outcomes during cranial SRS. Results: Five key studies were identified, including clinical case reports, dosimetric analyses, and phantom models. Gamma Knife demonstrated the lowest exposure, ranging from 1.5 to 3.1 mGy in legacy systems down to 0.49 to 1.28 mGy with modern equipment. CyberKnife reported fetal doses of ~42 mGy. For additional linear accelerator (LINAC) systems, modeling data suggested exposure in the low tens of milligrays due to increased scatter and leakage radiation. Across platforms, fetal dose correlated directly with target distance, treatment duration, internal scatter, machine leakage, and delivery system design. No adverse maternal or fetal outcomes were reported, and all recorded doses remained well below deterministic injury thresholds. Conclusions: Although the ideal fetal radiation dose is zero, available evidence indicates that fetal exposure during SRS remains below accepted thresholds for deterministic effects regardless of SRS treatment modality. Gamma Knife demonstrates the most favorable dosimetric profile due to reduced leakage and dedicated intracranial design. When treatment cannot be delayed, SRS may be considered in selected pregnant patients with individualized planning and multidisciplinary input. Further standardized studies are needed to refine comparative safety across platforms.