Radiation-Induced Alopecia in Patients Undergoing Intracranial Radiation Therapy: A Systematic Review

Radiation-induced alopecia (RIA) is a common side effect of cranial and head-and-neck radiotherapy that can be temporary or permanent, depending on radiation dose and hair follicles to recover. Since RIA can impact patients' self-image and quality of life, establishing dose thresholds and prevention strategies are essential for patient counseling and treatment planning. A PRISMA-guided systematic review was conducted using PubMed, Embase, Scopus, Web of Science, and Cochrane Central, including studies that reported RIA incidence, severity, persistence or scalp dose metrics in patients receiving external-beam radiotherapy. Fifteen studies (≈1,500 patients) were included, covering a range of techniques including photon-based modalities (3DCRT, IMRT, VMAT), proton therapy, hippocampus-sparing whole-brain radiotherapy (WBRT), and scalp-avoidance approaches. Across modalities, near-maximum scalp dose (D2%) and volumetric parameters consistently correlated with RIA severity. Temporary RIA typically occurred at ∼20 Gy, whereas permanent RIA was observed at mean doses above 30 to 36 Gy or D2% doses approximately 45 to 50 Gy. Proton NTCP and gEUD models showed strong predictive performance (AUC 0.8 to 0.9) and external validity, supporting their use for real-time plan evaluation. Pediatric patients, especially those receiving craniospinal irradiation with intensive chemotherapy, experienced permanent RIA at lower dose thresholds (∼21 Gy). Technical strategies such as scalp-avoidance VMAT and hippocampus-sparing WBRT reduced scalp dose and preserved hair without compromising tumor control. Although patient-reported outcomes were infrequently assessed, available data consistently highlighted significant psychosocial impact and patient interest in restorative interventions. RIA is a reproducible, dose-dependent effect with well-defined scalp dose thresholds. Routine scalp contouring, minimizing near-maximum hotspots, and applying scalp-sparing techniques are feasible and clinically impactful strategies. Integration of NTCP modeling and standardized quality-of-life assessments offers personalized risk prediction, supports informed treatment decision-making, and improves survivorship care.