No detectable early subclinical cardiotoxicity within 12 weeks of thoracic radiotherapy under predominantly low cardiac dose exposure: a prospective cohort study

BACKGROUND: Early radiation-induced cardiac injury in patients receiving thoracic radiotherapy (RT) remains insufficiently characterized. Global longitudinal strain (GLS) and circulating biomarkers such as high-sensitivity cardiac troponin T (hs-cTnT) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) may detect subclinical myocardialdamage. METHODS: This prospective single-center cohort study enrolled 47 adults with thoracic malignancies treated with curative-intent RT. Cardiac assessments were performed at baseline, 1 week, and 12 weeks post-RT. GLS was measured by two-dimensional speckle-tracking echocardiography, and hs-cTnT and NT-proBNP were quantified using high-sensitivity immunoassays. Mean heart dose (MHD) was categorized as < 10 Gy or ≥ 10 Gy to explore dose-stratified differences within this predominantly low-dose exposure cohort. Temporal changes and dose-stratified differences were analyzed using non-parametric tests. RESULTS: GLS remained stable across timepoints (median - 18.06% at baseline, - 18.72% at week 1, and - 18.59% at week 12; p = 0.650). Similarly, hs-cTnT showed no significant variation (7.30, 7.50, and 6.60 ng/L, respectively; p = 0.842), and NT-proBNP demonstrated modest, non-significant increases (43.0, 48.5, and 55.5 pg/mL; p = 0.797). Stratification by MHD revealed no significant differences in GLS or biomarker levels at any timepoint. No dose-dependent associations were observed These findings were consistent across subgroups and in sensitivity analyses restricted to completers, in a cohort with a median MHD of 5.1 Gy. CONCLUSIONS: Contemporary thoracic RT was not associated with detectable early subclinical cardiotoxicity within the first 12 weeks under predominantly low cardiac dose exposure. Early cardiac alterations may depend on higher radiation exposure or longer follow-up, supporting longitudinal surveillance strategies.