KEY POINTS
- This cross-sectional study included 4,908 patients treated with three-dimensional conformal or intensity-modulated breast radiotherapy from 2008 to 2018 at a tertiary centre in Canada. The primary analysis included 2,223 patients with left-sided breast cancer.
- During a median follow-up of 10.8 years, the 10-year cumulative incidence of a cardiac event or coronary artery disease was 5.0% (95% confidence interval, 4.1%–6.0%).
- A data-derived maximum left anterior descending coronary artery dose threshold of 12 Gy equivalent dose in 2-Gy fractions best stratified cardiac risk. Among patients with left-sided disease, this metric showed better discrimination than mean heart dose: C-index 0.58 versus 0.53.
- A maximum left anterior descending coronary artery dose of at least 12 Gy was independently associated with increased cardiac risk (subdistribution hazard ratio 1.81, 95% confidence interval 1.04–3.16; p=0.04). Mean heart dose of at least 2 Gy was not associated with risk (p=0.99).
- The 12 Gy equivalent-dose threshold corresponds to approximately 10.5 Gy in 16 fractions of 2.66 Gy or 7 Gy in 5 fractions of 5.2 Gy.
CLINICAL TAKEAWAY
Maximum left anterior descending coronary artery dose may provide additional long-term cardiac risk information beyond mean heart dose and could be considered during breast plan evaluation. However, the threshold was data-derived in a single-centre observational cohort and showed modest discrimination, so this is high-relevance evidence rather than a validated universal planning constraint.