[Screening for lung cancer: present and future]

A certified method for lung cancer screening in Japan is the combination of chest X-ray and sputum cytology. The chest Xray examination is intended primarily for the detection of peripheral-type lung cancer. Interpretation of the films should be performed by two different physicians, and the films of screenees suspected to have abnormal shadow should be compared to the same screenee's films from previous screening visits. Sputum cytology is conducted for heavy smokers, and is useful for early detection of central lung cancer. The efficacy of this lung cancer screening method has been shown in several case control studies. There are some problems to solve i. e., a low rate of attendance and inadequate quality control. Low-dose thoracic CT screening is performed with an exposure within a single breath hold, and its interpretation can be conducted with films, CRT, or a LCD monitor. Even when taken at low doses, the radiation exposure dose is large compared to a chest X-ray, being about 3-10 times greater than the absorbed dose and 20-40 times greater than the effective dose. Since the radiation dose in a usual clinical condition is much higher, the clinical condition is not recommended for screening. Concerning the efficacy of low-dose CT screening for heavy-smokers, a positive result was reported in June 2011, and further detailed analyses are required. There are still some problems to solve i. e., the management of undiagnosed shadows, harm caused by the screening, quality control, and efficacy in non-smokers.