Why does the annual CT scan still fail to screen for lung cancer?

Last year, a relative and his family had a general physical examination on time every year, including a lung CT. As a result, lung cancer was found in last year’s CT. The interval between the two CT scans was one year. Why can’t CT find early lung cancer?

it can be said that such examples are not rare. Many people have heard of it. So why does this happen? Is annual physical examination a waste of money? It is estimated that many people have it in their hearts, which inevitably leads to doubts.

the truth is that CT every year does not guarantee that early lung cancer can be screened completely; there are exceptions to everything, and 100% can not be achieved. Many factors can affect the timeliness and accuracy of screening results.

for general physical examination, low-dose CT or ordinary chest X-ray is sufficient. Ordinary chest X-ray can distinguish lung lesions with diameter more than one centimeter. Low dose CT can distinguish lung lesions with diameter more than 0.1 cm.

therefore, when lung lesions are less than 1 cm or less than 0.1 cm, low-dose CT and ordinary chest X-ray are far from enough. If the early lung tumor is located in a relatively hidden place, such as behind the ribs or close to the heart, it is easy to ignore on imaging, so it will not be diagnosed. This probability may be 0.7%, tens of thousands or even hundreds of thousands of them. But for individuals, the probability is 100 percent.

the diagnostic level of each doctor is different. Although CT and chest X-ray are relatively objective examinations, they still need to be interpreted manually. Even though the most advanced intelligent AI imaging diagnosis system is still unable to replace imaging diagnostic doctors.

for small lung lesions, most of the time, it is impossible to directly judge the nature of lung lesions through imaging. The doctor with rich clinical experience can make preliminary judgment and orientation guidance according to the history and the condition of the film. The doctor with less experience may neglect it or even judge in the opposite direction.

take a very simple example, such as chest X-ray or lung CT finding small pulmonary nodules. So it is impossible to determine the nature of the film alone, whether it is malignant or benign. Most doctors may suggest a follow-up visit of three months or six months, and some doctors may not necessarily recommend reexamination. If it is the early stage of lung cancer, when the nodules gradually grow up and cause symptoms, most of them become middle and late stage.

the doubling time refers to the time required to double the nodule volume. In the 1990s, chest X-ray film and CT were used to directly measure the diameter of pulmonary nodules. The data were brought into the volume calculation formula v = 6 × AB2, and the doubling time VDT = t × log2 / log, so as to obtain the doubling time of nodules. However, the numerical significance of this measurement is limited, it is not very correct, and the error is very large.

according to big data statistics, in addition to chest X-ray or CT findings, the doubling time of lung cancer is more closely related to the types of lung cancer, and there are individual differences. The doubling time of smokers is faster than that of non-smokers. For example, the doubling time of most non-small cell lung cancer is between 180 days, while the doubling time of small-cell lung cancer can be shortened to 80 days. Moreover, smoking will accelerate, and the larger the tumor, the faster the doubling time. Therefore, it will grow exponentially.

Based on the above, it is very common that no lung cancer was found a year ago, but a year later, advanced lung cancer occurred. Therefore, physical examination is necessary, but we can not rely on it. Physical examination is only an early sign, and it can’t cover everything. When the corresponding discomfort symptoms appear after the physical examination, we should review and see a doctor in time; instead of thinking that everything is OK after the physical examination, it belongs to paralysis. Early detection, early diagnosis and early treatment of malignant tumors, especially lung cancer, are the most important factors related to long-term survival. HEALTHY LIFE