Beyond mean heart dose: quantitative impact of sub-structure spatial dosimetrics on subclinical myocardial strain in thoracic radiotherapy.

PURPOSE: To evaluate the spatial dosimetric relationships between cardiac substructures and hyper-acute subclinical myocardial strain alterations after thoracic intensity-modulated radiotherapy (IMRT).

METHODS

Forty patients with thoracic malignancies were prospectively enrolled. Two-dimensional speckle-tracking echocardiography (2D-STE) was performed at baseline and 1-2 days post-radiotherapy to assess left ventricular global longitudinal strain (LVGLS) and right ventricular free wall longitudinal strain (RVFWLS). Cardiac substructures, including the atrioventricular node (AVN), sinoatrial node (SAN), and right coronary artery (RCA), were contoured standardized. Acute subclinical strain alteration was defined as a ≥ 15% relative reduction from baseline. Optimal dosimetric cutoffs were determined via Maxstat analysis, and independent predictors were identified using multivariable logistic regression.

RESULTS

Immediately post-radiotherapy, the incidence of hyper-acute subclinical strain alterations was 65% (26/40) for the right ventricle and 40% (16/40) for the left ventricle, captured by 2D-STE prior to any conventional LVEF decline. Multivariable analysis identified AVN D mean ≥ 6.83 Gy as an independent predictor of acute LV strain alterations (OR = 4.49, 95%CI: 3.46-5.82, P < 0.001). For the right ventricle, RCA V 5 ≥ 77.56% (OR = 6.0, 95%CI: 4.26-8.53, P < 0.001), SAN D max ≥ 33.36 Gy (OR = 3.07, 95%CI: 2.11-4.44, P < 0.001) were independent predictors.

CONCLUSION

Hyper-acute subclinical strain alterations are highly prevalent immediately after thoracic radiotherapy, with right-sided structures exhibiting enhanced radiosensitivity. Dosimetric metrics of the AVN, SAN, and RCA serve as independent predictors. Although these data-driven cutoffs are exploratory and hypothesis-generating, they suggest that independent sparing of the conduction system and coronary vasculature should be considered in precision radiotherapy, warranting validation in future large-scale, multicenter trials.