Cardiovascular risk assessment in lung cancer screening scans: do coronary and aortic calcium scores yield comparable risks for individual subjects?

Purpose: Lung cancer screening trials may provide information about cardiovascular risk. It is not yet clear whether coronary scores from non-gated scans or aortic scores are more suited for this purpose. We examined whether risk stratification based on aortic calcifications places patients into similar groups as risk based on coronary calcium scores derived from non-gated lung cancer screening studies. Method and materials: We included 1091 baseline scans from subjects participating in a lung cancer screening trial (NELSON). Scans had been acquired at two centers using 16 x 0.75 mm collimation and a low-dose, non-contrast, non-ECG-gated scanning protocol. To control image noise, 3mm sections were reconstructed every 1.4mm. Aortic and coronary calcifications were scored by two observers (130 HU threshold). For coronary calcifications four atherosclerotic risk categories were defined based on Agatston score (?10, 11-100, 101-400, >400). Since no categorization is available for aortic scores we assigned four categories, each containing the same number of subjects as the respective coronary categories. To assess the agreement, we calculated linearly weighted kappa statistics (categories) and Spearman rank correlation coefficients (scores). Results: The number of subjects was 327, 156, 175 and 433 in the four coronary risk categories, respectively. The aortic calcium score assigned 526 (48%) subjects to the same risk category as the coronary score. Linearly weighted kappa statistic was 0.37, and Spearman rank correlation between scores was 0.51. Conclusion: While yielding similar results, aortic and coronary calcium scores cannot be used interchangeably for assessing individual arteriosclerotic risk from lung cancer screening studies.