With the improvement of living standard, people pay more and more attention to the usual health checkups, and the application of CT in lung is increasing, and the detection of lung nodules is significantly more than before. To address the many issues of lung cancer screening that patients are concerned about, I would like to share with you the key points of the recent NCCN lung cancer screening guidelines for your reference. The NCCN (National Comprehensive Cancer Network) published its first lung cancer screening guidelines in late October 2011. The guidelines were based on the results of the National Lung Cancer Screening Study (NLST) published by the New England Journal of Medicine (NEJM) in August 2011. The study applied low-dose spiral CT (LDCT) to a high-risk population for routine annual screening and found that LDCT screening reduced lung cancer mortality by 20% and reduced mortality from any cause by 7% compared to chest radiograph screening. Based on this result, the guidelines explicitly include LDCT as a lung cancer screening tool and make different guidelines for the management of different findings on LDCT. In general, the NCCN guidelines recommend annual low-dose spiral CT of the lungs for people at high risk for lung cancer. High-risk groups are those who are: A. 55-74 years of age, who are smoking or have quit smoking for less than 15 years, and have a smoking index greater than 30 pack-years. B. Those who are older than 50 years old, have a smoking index greater than 20 pack-years, and have a combination of one of the following conditions: history of tumor; history of lung disease; family members with lung cancer; residential radon exposure and occupational exposure to carcinogens (including arsenic, chromium, asbestos, nickel, cadmium, beryllium, silica and diesel fumes). The above high-risk groups of lung cancer are recommended to have low-dose spiral CT (LDCT) examination annually for at least 3 years (the optimal duration of years is unknown), while routine LDCT examination is not recommended for other medium and low-risk groups. Depending on the CT findings, different management measures will be taken: A. No pulmonary nodules: Annual LDCT for at least 3 years (optimal duration not yet known). B. Detection of solid or partially solid nodules in the lung (nodules without benign calcification, fatty or inflammatory manifestations): a. ≤ 4 mm, annual LDCT for at least 3 years (optimal duration not yet known). b. >4-6 mm, LDCT after 6 months, if no growth, LDCT after 12 months, still no growth, LDCT every year for at least 2 years (optimal duration not yet known). c. >6-8 mm, 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 (optimal duration is not known). d. >8mm, consider PET/CT examination, if lung cancer is suspected, surgery or biopsy; if lung cancer is not considered, dynamic observation as above. In the above cases under dynamic observation, if nodules are found to grow, surgical resection is recommended. e. If endobronchial nodules are found, LDCT will be repeated after 1 month, and if they do not subside, fiberoptic bronchoscopy will be done to clarify. C. Detection of pulmonary ground glass shadow (GGO) or other non-solid nodules (without clear benign indication): a. <5mm< font="">, repeat CT after 12 months, if stable, annual LDCT for at least 2 years (optimal duration is not known). b. 5-10 mm, repeat CT after 6 months, if stable, annual LDCT for at least 2 years (optimal duration not yet known). c. >10mm, review LDCT after 3-6 months, if stable, LDCT can be reviewed after 6-12 months, or biopsy or surgical resection. If the nodule is found to be enlarged or solid during the above dynamic observation, surgical resection should be performed, except for those with a diameter <5mm< font=""> who can be considered for dynamic review of LDCT in 3-6 months. These are the guidelines for LDCT lung screening in the NCCN guidelines. In addition, the majority of patients and friends are concerned about the accuracy of screening, the malignancy ratio of various nodules and the impact of CT radiation on the body, and the following information on these aspects is provided for your reference. The malignancy rate of various pulmonary nodules: Li et al. reported that the malignancy rate of ground glass nodules with a diameter of 3-20 mm was 59%, the malignancy rate of mixed images of ground glass nodules + solid nodules was 48%, and the malignancy rate of solid nodules was 11%. The majority of lung cancers presenting with ground glass shadow are adenocarcinoma in situ, which is previously referred to as fine bronchoalveolar carcinoma, with a 100% survival rate at 5 years after surgery. Lung cancers that show solid or mixed solid nodules are mostly invasive and fast-growing lung cancers. 2.Leakage rate of LDCT screening for lung cancer: Low-dose spiral CT screening still has a certain degree of leakage. It was reported that among 88 patients who were finally diagnosed with lung cancer, 33 (37.5%) had been missed in 39 LDCTs, of which 23 (59%) were due to LDCT failures and 16 (41%) were due to physician reading errors. Reasons for poor LDCT display included: A. 91% due to microscopic glassy lesions B. 83% due to lesions that overlapped, were obscured, or were similar to normal lung tissue structures (e.g., pulmonary vessels). 87% of the missed readers were due to underlying lung disease such as emphysema, tuberculosis and pulmonary fibrosis. 3, LDCT radiation risk issues: How much will frequent CT affect the body? I believe this is a common concern, and its main risk is to induce the occurrence of malignant tumors. The average radiation of traditional CT scan is 7mSv, while the average effective radiation of spiral CT with low dose technology is 1.4mSv, which is about 10 times of the radiation of chest X-ray (comparison reference: the average background radiation of the world is 2.4mSv/year, 0.001mSv/hour of airplane, 1mSv/year of a pack of cigarettes per day, 0.5mSv/year of soil and air, 0.2mSv/year of food. (0.2mSv/year for soil and air and 0.2mSv/year for food). Brenner et al. concluded, based on a study of Japanese A-bomb survivors, that if a 50-year-old woman who smoked underwent annual chest CT (radiation dose 5.2 mSv/session) until age 75, the estimated probability of radiation-induced lung cancer was 0.85%; whereas the risk of lung cancer from a single lung CT scan (radiation dose 5.2 mSv) was about 0.056%. Mascalchi et al. reported the application of multi-row CT (radiation dose of 3.3 mSv) and single-row CT (radiation dose of 5.8 or 7.1 mSv) to annual lung cancer screening scans in people aged 50-70 years for 4 years, and calculated the risk of lung cancer due to radiation to be 0.011% for multi-row CT and 0.020-0.024% for single-row CT. It seems that the risk of CT radiation does exist, but it is clearly acceptable compared to the 20% reduction in lung cancer mortality that CT can achieve. The CT images of ground glass and solid nodules are shown below: from left to right, pure GGO (ground glass), mixed GGO, and solid nodules.