Dosimetric and therapeutic effectiveness of high-dose-rate radionuclide sources in breast cancer brachytherapy: A systematic review.

BACKGROUND: High-dose-rate (HDR) brachytherapy is a widely used treatment modality for breast cancer, providing highly localized radiation delivery with improved normal tissue sparing. The choice of radionuclide source plays an important role in determining dosimetric characteristics and the available evidence for clinical effectiveness. OBJECTIVE: This systematic review aims to evaluate and compare the dosimetric properties and therapeutic effectiveness of commonly used HDR radionuclide sources like Iridium-192 (¹⁹²Ir), Cobalt-60 (⁶⁰Co), and Ytterbium-169 (¹⁶⁹Yb) in breast cancer brachytherapy. METHODS: A systematic literature search was conducted across PubMed, Scopus, Embase, and Google Scholar for studies published between 2005 and 2026. Studies reporting quantitative dosimetric parameters and clinical outcomes for HDR brachytherapy were included. Data extraction focused on TG-43 parameters, dose-volume measurements, and clinical endpoints. Study selection followed PRISMA guidelines. RESULTS: Sixteen studies met the inclusion criteria, comprising randomized phase three trials (GEC-ESTRO 10-year update), 30-year phase two results, retrospective cohort analyses, and Monte Carlo simulations. The dose rate constant (Λ) was similar among radionuclides (approximately 1.08-1.20 cGy·h⁻¹·U⁻¹). However, substantial differences were observed in dose gradients and tissue penetration. ¹⁶⁹Yb demonstrated the steepest dose fall-off and superior organ-at-risk sparing due to its low average photon energy. ⁶⁰Co, provided deeper tissue penetration and greater robustness to tissue heterogeneity. ¹⁹²Ir offered an optimized dosimetric profile and the most extensive clinical validation. Robust clinical outcome data were available for ¹⁹²Ir, demonstrating local control rates exceeding 90%. Limited clinical evidence exists for ⁶⁰Co, while evidence for ¹⁶⁹Yb is currently restricted to dosimetric and Monte Carlo investigations. Emerging dosimetric innovations included deep learning-based dose prediction and model-based dose calculation algorithms. CONCLUSION: ¹⁹²Ir remains the standard HDR radionuclide, supported by the strongest long-term clinical evidence for target coverage, local control, toxicity, and cosmetic outcomes. Treatment-planning studies indicate that ⁶⁰Co provides dosimetric performance comparable to ¹⁹²Ir, whereas evidence for ¹⁶⁹Yb is currently limited to dosimetric and Monte Carlo investigations that suggest potential organ-at-risk sparing without clinical validation. These findings support a personalized approach to radionuclide selection based on clinical evidence, treatment objectives, and treatment geometry. Additional prospective clinical studies, particularly for ¹⁶⁹Yb and APBI-specific applications of ⁶⁰Co, are needed to establish long-term clinical outcomes.