Evaluation of Cardiac Function After Stereotactic Body Radiation Therapy for Lung Tumors: Results of the Prospective Explorative Heart-Lung Study

Purpose: Several studies show associations between cardiac radiation dose and cardiac morbidity or overall survival. To evaluate cardiac toxicity of radiation therapy in the absence of another cardiotoxic agent, we set up a prospective pilot study evaluating cardiac function using a wide range of diagnostic modalities in early-stage non-small cell lung cancer (NSCLC) patients with a tumor in close proximity to the heart. Methods and Materials: The HALO study was a prospective, single-arm, multicenter observational pilot study. Patients scheduled for stereotactic body radiation therapy for stage 1A to 2B NSCLC, or a solitary lung metastasis, with a tumor <3 cm from the heart were included. Cardiac function was evaluated using electrocardiography (ECG), laboratory exams, echocardiography, cardiac magnetic resonance imaging (CMR), and questionnaires at pretreatment and 3 and 12 months poststereotactic body radiation therapy. To assess dose effects, generalized linear models were fitted between segmental radiation dose and strain difference between time points, for longitudinal, circumferential, and radial myocardial strain. Results: Ten patients were included in the study, of whom 8 were included for analysis, yielding 90 cardiac segments for analysis. No significant differences were found in any of the ECG, laboratory exams, echocardiography, CMR, or questionnaire measurements. The dose effects were small and translated to a possible worsening of myocardial strain in the highest cardiac dose segments, with an absolute difference of 2.8%. Conclusions: In these early-stage NSCLC patients with mean cardiac doses of 4 Gy, no clinically relevant dose-related cardiac adverse events nor significant changes in global cardiac function were observed after multimodal cardiac evaluation during 12 months of follow-up. Dose-dependent effects of radiation therapy on myocardial strain were not observed in this small pilot study.