Risk of Cardiovascular Toxicity According to Tumor Laterality Among Older Patients With Early Stage Non-small Cell Lung Cancer Treated With Radiation Therapy

Background: The long-term risk of cardiovascular outcomes from either stereotactic body radiation therapy (SBRT) or three-dimensional conformal radiation therapy (3DCRT) plus intensity-modulated radiation therapy (IMRT) to treat early stage non-small cell lung cancer (NSCLC) is largely unknown. As continued adoption of SBRT accelerates, it is important to delineate unforeseen cardiovascular risks associated with treatment.

Research question: Does the long-term risk of cardiovascular outcomes for patients with early stage NSCLC treated with either SBRT or 3DCRT plus IMRT differ by tumor laterality?

Study design and methods: Data from the Surveillance, Epidemiology, and End Results registry linked to Medicare was analyzed to identify a sample of 3,256 patients (1,506 treated with SBRT and 1,750 treated with 3DCRT plus IMRT) with node-negative stage I or IIA NSCLC. Cardiovascular events were identified using diagnosis codes, and outcomes were compared between left- and right-sided tumors. We assumed that tumor laterality was random and that the radiation field for left-sided tumors likely would result in greater dose to cardiac tissues. Cox regression models were fit to quantify the association of laterality on outcomes.

Results: Patients were followed up for a median of 2 years. Those treated with SBRT showed no difference in hazard of any cardiovascular outcomes by tumor laterality, including the cardiovascular composite (hazard ratio [HR] comparing left- vs right-sided tumors, 0.98; 95% CI, 0.84-1.15). In contrast, patients treated with 3DCRT plus IMRT showed a greater risk of congestive heart failure (HR, 1.23; 95% CI, 1.01-1.48) and percutaneous coronary artery intervention (HR, 2.24; 95% CI, 1.12-4.47).

Interpretation: Patients with left- vs right-sided early stage NSCLC showed similar rates of cardiovascular events when treated with SBRT. However, these patients also showed higher rates of select cardiac events when they were treated with 3DCRT plus IMRT. This study provides evidence that SBRT may provide a safer option over 3DCRT plus IMRT for patients with left-sided early stage NSCLC and underscores the need for long-term follow-up for patients treated with radiation therapy.