Comparability of Pulmonary Nodule Size Measurements among Different Scanners and Protocols: Should Diameter Be Favorized over Volume?

BACKGROUND: To assess the impact of the lung cancer screening protocol recommended by the European Society of Thoracic Imaging (ESTI) on nodule diameter, volume, and density throughout different computed tomography (CT) scanners. METHODS: An anthropomorphic chest phantom containing fourteen different-sized (range 3-12 mm) and CT-attenuated (100 HU, -630 HU and -800 HU, termed as solid, GG1 and GG2) pulmonary nodules was imaged on five CT scanners with institute-specific standard protocols (P$_{S}$) and the lung cancer screening protocol recommended by ESTI (ESTI protocol, P$_{E}$). Images were reconstructed with filtered back projection (FBP) and iterative reconstruction (REC). Image noise, nodule density and size (diameter/volume) were measured. Absolute percentage errors (APEs) of measurements were calculated. RESULTS: Using P$_{E}$, dosage variance between different scanners tended to decrease compared to P$_{S}$, and the mean differences were statistically insignificant (p = 0.48). P$_{S}$ and P$_{E(REC)}$ showed significantly less image noise than P$_{E(FBP)}$ (p < 0.001). The smallest size measurement errors were noted with volumetric measurements in P$_{E(REC)}$ and highest with diametric measurements in P$_{E(FBP)}$. Volume performed better than diameter measurements in solid and GG1 nodules (p < 0.001). However, in GG2 nodules, this could not be observed (p = 0.20). Regarding nodule density, REC values were more consistent throughout different scanners and protocols. CONCLUSION: Considering radiation dose, image noise, nodule size, and density measurements, we fully endorse the ESTI screening protocol including the use of REC. For size measurements, volume should be preferred over diameter.