Lung cancer is currently the leading cause of cancer-related death worldwide. Current five-year survival estimates for non-small cell lung cancer range from 73% for stage IA disease to 13% for stage IV disease. The early detection of lung cancer in early stages or stage IA is associated with better prognosis for disease-free survival. In 2011, the National Lung Screening Trial (NLST) reported that participants who received LDCT had a 15 to 20 percent lower risk of dying from lung cancer than participants who received standard chest radiography.
　　LDCT is known to be the optimal imaging modality for early detection of lung cancer, however, there are challenges and difficulties for diagnosing early lung cancer, as these include: (1). Variable inclusion criteria of subjects receiving LDCT screening in different regions due to the variance in epidemiology or the predisposing factors. (2) Existence of the variance in CT classification of part-solid from pure ground glass nodules (GGNs). (3) Inconsistent image interpretation of GGNs’ uniformity (homogeneous vs. heterogeneous). (4) Potential variation in the manual size measurement, since growth is defined as an increase in the size of > 1.5 mm (>1.8 mm3) in Lung-Rads 1.1. (5) The follow-up management paradigm may differ from different societies or versions for a positive screening result (e.g. In Lung-RADS 1.1, the pure GGNs with the sizes < 30 mm and unchanged GGNs with the sizes ≧ 30 mm are classified to category 2. The newly developed GGNs with the sizes ≧ 30 mm fall into category 3. Nonetheless, the GGNs classified into categories 2 or 3, based on the Lung-RADS 1.1, and were reported to have a higher malignancy rate than expected). (6) CT findings or signs (nodule pattern, size, shape, interface, margin, contour, attenuation, vessel relationship, air-bronchogram and vacuole sign) for differentiating benign and malignant nodules, CT predictors to differentiate non-invasive from invasive adenocarcinoma. (7) Challenge from the false positive screening results. (8) There is no definite endpoint for the follow-up period of GGNs that are dormant in growth; and (9) over-diagnosis and over-treatment of the nodules that are detected incidentally or by screening.