Cardiac Dose and Survival Outcomes Following Stereotactic Body Radiation Therapy for Primary and Metastatic Lung Tumors: A Substructure-Based Analysis.

PURPOSE: This study investigates the association between radiation dose to the heart base and other cardiac substructures and overall survival (OS) following stereotactic body radiation therapy (SBRT) for central and ultracentral lung tumors.

METHODS AND MATERIALS: A retrospective analysis was performed on patients treated within the SBRT registry (2011-2023). Autosegmentation was used to contour the whole-heart and cardiac substructures, whereas the heart base-overlapping the ascending aorta and including coronary origins and the sinoatrial node-was manually contoured. Mean (Dmean) and near-maximum doses (D0.03, highest dose to 0.03 cm3) were converted to equivalent 2 Gy fractions (EQD₂, α/β = 3 Gy). Optimal dose cut-points were defined to stratify patients into high- and low-dose groups. Cox regression models, adjusted for age, sex, tumor type, and volume, assessed the association between cardiac dose and OS; additional sensitivity analyses included bronchial Dmax.

RESULTS

Among 82 treated patients, 66 were evaluable for dosimetry of cardiac structures and survival analysis. Median age was 67 years; 68% were male. Most lesions were metastases (62.5%) and evenly split between central (54.5%) and ultracentral (45.5%) locations. Higher EQD₂ Dmean to the left atrium (hazard ratio [HR], 2.89; P = .04) and superior vena cava (HR, 2.56; P = .03), and higher D0.03 to the superior vena cava (HR, 3.12; P = .004) and right ventricle (HR, 2.23; P = .04) were independently associated with worse OS. After sensitivity analysis, associations for the superior vena cava remained significant, whereas others were attenuated to statistical trends. A higher mean dose to the heart base showed a strong trend toward reduced survival (HR, 3.70; P = .05).

CONCLUSIONS

Higher radiation doses to the left atrium, superior vena cava, and right ventricle were independently associated with worse OS after SBRT for central and ultracentral lung tumors, underscoring the importance of cardiac-substructure-specific dose constraints in SBRT planning. Moreover, a clear trend toward reduced survival with higher doses to the base of the heart underscores the importance of this region as a potential target for future dose-sparing strategies.