Frequency and distribution of incidental findings deemed appropriate for S modifier designation on low-dose CT in a lung cancer screening program

•Use of the Lung-RADS S modifier was common, present for 261 of 581 (45%) participants.•Coronary artery calcification was most frequent observation warranting S modifier.•Inter-observer variability between radiologists was substantial (kappa of 0.2).•Guidelines for all incidental findings on screening chest CT are clearly needed.