Does mean heart dose sufficiently reflect coronary artery exposure in left-sided breast cancer radiotherapy? : Influence of respiratory gating.

PURPOSE: With extensive use of systemic treatment, the issue of cardiac mortality after breast cancer radiation (RT) is still important. The aim of our analysis was to clarify whether the dose to one surrogate parameter (e. g., mean heart dose, as used in most studies) reflects the dose to the other cardiovascular structures especially the left anterior descending artery depending on breathing-adapted RT.

PATIENTS AND METHODS: A total of 130 patients who underwent adjuvant RT (50.4 Gy plus boost 9-16 Gy) were evaluated. In all, 71 patients were treated with free-breathing and 59 patients using respiratory monitoring (gated RT). Dosimetric associations were calculated.

RESULTS: The mean dose to the heart (Dmean heart) was reduced from 2.7 (0.8-5.2) Gy to 2.4 (1.1-4.6) Gy, the Dmean LAD (left anterior descending artery) decreased from 11.1 (1.3-28.6) Gy to 9.3 (2.2-19.9) Gy with gated RT (p = 0.04). A significant relationship was shown for Dmean heart-Dmean LAD, V25heart-Dmean LAD and Dmax heart-Dmax LAD for gated patients only (p < 0.01). For every 1 Gy increase in Dmean heart, mean LAD doses rose by 3.6 Gy, without gating V25 ≤5 % did not assure a benefit and resulted in Dmean LAD between 1.3 and 28.6 Gy.

CONCLUSION: A significant reduction and association of heart and coronary artery (LAD) doses using inspiratory gating was shown. However, in free-breathing plans commonly measured dose constraints do not allow precise estimation of the dose to the coronary arteries.