The abnormal shadows in the lungs can be classified as solid nodular shadows, ground glass shadows and mixed shadows of ground glass shadows + solid nodules. As for the question of concern, is it cancerous? It has been reported in the literature that among nodules of 0.3-2 cm in diameter, the malignancy rate of ground glass shadow is 59%, the malignancy rate of mixed ground glass shadow + solid nodules is 48%, and the malignancy rate of solid nodules is 11%. Most of the lung cancers with ground glass shadow are in situ adenocarcinoma, which is previously known as fine bronchoalveolar carcinoma, with a 100% survival rate at 5 years after surgery. Lung cancers that show solid or mixed solid nodules are more aggressive and fast-growing lung cancers. In addition, people at high risk for lung cancer are: 1. 55-74 years old, are smoking or have quit smoking for less than 15 years, and have a smoking index greater than 30 pack years. 2. Those who are older than 50 years old, have a smoking index greater than 20 pack years, and combine one of the following conditions: history of tumor; history of lung disease; lung cancer patients in family; occupational exposure to radon and carcinogenic substances in residence (including arsenic, chromium, asbestos, nickel, cadmium, beryllium, silica and diesel fumes). Second, how much will frequent CT affect the body? There is a common question of the effect of imaging on the body involved here. First of all, it is important to know that milli-sievert (mSv) is the basic unit of radiation dose. The primary unit of radiation dose is the sievert (sv), but the sievert is a very large unit, so milli-sievert (mSv) is usually used. The worldwide average background radiation dose is 2.4 mSv/year, 0.001 mSv/hour in an airplane, 1 mSv/year from a pack of cigarettes per day, 0.5 mSv/year from dirt and air, and 0.2 mSv/year from food. The average radiation dose of conventional CT scan is 7mSv, while the average effective radiation dose of spiral CT with the application of low-dose technology is 1.4mSv, and this dose is about 10 times the radiation dose of chest X-ray. III. Current recommendations Referring to the NCCN guidelines, management measures depending on the CT findings: 1. No pulmonary nodules: annual LDCT examination for at least 3 years (the optimal duration is not known). 2. Solid or partially solid pulmonary nodules (nodules without benign calcification, fatty or inflammatory manifestations) found: (1) ≤4mm, annual LDCT for at least 3 years (optimal duration of years not yet known) (2) >4-6mm, review LDCT after 6 months, if no growth, review LDCT after 12 months, still no growth, review LDCT every year for at least 2 years (optimal duration is unknown). (3) >6-8mm, review LDCT after 3 months, if there is no growth, review LDCT after 6 months, no change then review LDCT after 12 months, still no change, review LDCT every year for at least 2 years (the best duration is not known). (4) >8mm, consider PET/CT examination, if lung cancer is suspected, surgery or biopsy; if lung cancer is not considered, dynamic observation as above. (5) find endobronchial nodules, review LDCT after 1 month, if it does not subside, do fiberoptic bronchoscopy for clarification. 3.Find pulmonary ground glass shadow (GGO) or other non-solid nodules (no clear benign indication): (1) <5mm, repeat CT after 12 months, if stable, LDCT every year for at least 2 years (the best duration is not known). (2) 5-10 mm, CT review after 6 months, if stable, annual LDCT for at least 2 years (optimal duration not yet known). (3) >10mm, review LDCT after 3-6 months, if stable, LDCT can be reviewed after 6-12 months, or biopsy or surgical resection. If the nodules are found to be enlarged or solid during the above dynamic observation, they should be surgically removed except for those with diameters <5mm, which can be considered for dynamic review of LDCT in 3-6 months.