KEY POINTS
- The systematic review included 16 studies published from 2005–2026, spanning randomized and prospective clinical trials, retrospective cohorts, planning studies, Monte Carlo simulations, and emerging deep-learning dose-calculation methods.
- The three HDR sources differ markedly in physical characteristics: Ir-192 has a half-life of 73.8 days and average photon energy of 380 keV, Co-60 a 5.27-year half-life and 1.25-MeV photons, and Yb-169 a 32-day half-life with much lower 93-keV photon energy.
- Dose-rate constants were relatively similar—approximately 1.11 cGy·h⁻¹·U⁻¹ for Ir-192, 1.08 for Co-60, and 1.20 for Yb-169—but radial attenuation differed substantially. Yb-169 produced the steepest gradient and theoretically greatest OAR sparing, whereas Co-60 provided deeper penetration and less sensitivity to tissue heterogeneity.
- Ir-192 is the only source supported by mature breast clinical data. Across included studies, target D90 was approximately 92–96%, V100 95–98%, and local control generally exceeded 90%.
- In the randomized GEC-ESTRO APBI trial, 10-year local recurrence was 3.51% after multicatheter brachytherapy versus 1.58% after whole-breast irradiation, while grade 3 late effects were 1% versus 4%, supporting long-term efficacy and tolerability of Ir-192-based APBI.
- A separate phase II experience with 30-year follow-up reported an ipsilateral breast recurrence rate of 12.6%, excellent/good cosmesis in 75.6%, and grade 3 fibrosis in 2.2%, providing unusually mature evidence for the technique.
- Co-60 appears dosimetrically comparable to Ir-192 in planning studies and one boost series reported 98.5% 5-year local control, but dedicated APBI outcome data remain sparse. Yb-169 has no meaningful clinical breast outcome dataset and currently remains a dosimetric/Monte Carlo concept.
CLINICAL TAKEAWAY
For breast HDR brachytherapy, Ir-192 remains the evidence-based reference source because its dosimetric performance is backed by decades of clinical follow-up. Co-60 may be a practical alternative in selected systems, whereas the attractive OAR-sparing characteristics of Yb-169 require clinical validation before influencing source selection.