KEY POINTS
- This multicentre retrospective cohort included 633 women who received postoperative breast radiotherapy at two hospitals from 2011 to 2013. Median follow-up was 11.8 years; 99.5% were treated with three-dimensional conformal radiotherapy, without deep-inspiration breath-hold.
- The primary endpoint was first major adverse cardiac event, comprising cardiogenic death, myocardial infarction, coronary revascularisation, unstable angina, or heart failure. 29 patients (4.6%) experienced an event.
- Left anterior descending artery V40 was the strongest dosimetric predictor: each 1-percentage-point increase was associated with higher event risk (subdistribution hazard ratio 1.023, 95% confidence interval 1.005–1.040; p=0.010).
- A left anterior descending artery V40 of at least 18% was associated with more than twice the risk of major adverse cardiac events (subdistribution hazard ratio 2.333, 95% confidence interval 1.071–5.085; p=0.033). Adjusted 10-year incidence was 3.2% versus 1.4% below this threshold.
- The internally validated normal tissue complication probability model incorporated left anterior descending artery V40, age, and cardiac history and achieved an optimism-corrected C-index of 0.865. In five high-dose cases, volumetric modulated arc therapy replanning reduced mean V40 from 64.6% to 31.4% and projected 10-year excess risk from 8.8% to 3.0%.
CLINICAL TAKEAWAY
Left anterior descending artery high-dose exposure may provide more useful cardiac risk information than whole-heart dosimetry and could serve as an additional optimisation metric in breast radiotherapy planning. However, the evidence is retrospective, based on only 29 events in a predominantly East Asian cohort treated mainly with non-breath-hold three-dimensional conformal radiotherapy, and the model requires external validation.
SOURCE
International Journal of Radiation Oncology, Biology, Physics