Ultra-low dose computed tomography protocols using spectral shaping for lung cancer screening: Comparison with low-dose for volumetric LungRADS classification

Purpose: To compare Low-Dose Computed Tomography (LDCT) with four different Ultra-Low-Dose Computed Tomography (ULDCT) protocols for PN classification according to the Lung Reporting and Data System (LungRADS).Methods: Three hundred sixty-one participants of an ongoing lung cancer screening (LCS) underwent singlebreath-hold double chest Computed Tomography (CT), including LDCT (120kVp, 25mAs; CTDIvol 1,62 mGy) and one ULDCT among: fully automated exposure control ("ULDCT 1 "); fixed tube-voltage and current according to patient size ("ULDCT 2 "); hybrid approach with fixed tube-voltage ("ULDCT 3 ") and tube current automated exposure control ("ULDCT 4 ").Two radiologists (R1, R2) assessed LungRADS 2022 categories on LDCT, and then after 2 weeks on ULDCT using two different kernels (R1: Qr49 ADMIRE 4 ; R2: Br49 ADMIRE 3 ).Intra-subject agreement for LungRADS categories between LDCT and ULDCT was measured by the k-Cohen Index with Fleiss-Cohen weights.Results: LDCT-dominant PNs were detected in ULDCT in 87 % of cases on Qr49 ADMIRE 4 and 88 % on Br49 ADMIRE 3 .The intra-subject agreement was: ULDCT 1 = 0.89 95 %CI 0.82-0.96;ULDCT 2 = 0.90 0.81-0.98;ULDCT 3 = 0.91 0.84-0.99;ULDCT 4 = 0.88 0.78-0.97 on Qr49 ADMIRE 4 , and ULDCT 1 = 0.88 0.80-0.95;ULDCT 2 = 0.91 0.86-0.96;ULDCT 3 = 0.87 0.78-0.95;and ULDCT 4 = 0.88 0.82-0.94 on Br49 ADMIRE 3 .LDCT classified as LungRADS 4B were correctly identified as LungRADS 4B at ULDCT 3 , with the lowest radiation exposure among the tested protocols (median effective doses were 0.31, 0.36, 0.27 and 0.37 mSv for ULDCT 1 , ULDCT 2 , ULDCT 3 , and ULDCT 4 , respectively).Conclusions: ULDCT by spectral shaping allows the detection and characterization of PNs with an excellent agreement with LDCT and can be proposed as a feasible approach in LCS.