[Screening for lung cancer by low-dose computed tomography]

The primary screening method for lung cancer in Japan is the chest x-ray, although it is not the accepted international standard because its accuracy is lower than that of procedures used to detect other types of cancer. Since the incidence and mortality rate of lung cancer are higher than in many other cancers, more effective screening modalities need to be developed. Lung cancer screening was improved about ten years ago through the introduction of computed tomography (CT) scanning techniques. CT provides a higher level of accuracy in detecting early lung cancers and there have been reports of improvement in the five-year survival rate, although its effect on decreasing the mortality rate has not been demonstrated as yet. There are two significant disadvantages, however, associated with using CT for the detection of lung cancer. First, CT scanning results in a considerably higher level of radiation exposure than chest x-ray. Secondly, CT scanning is so sensitive that it can reveal shadows unrelated to lung cancer, resulting in additional, but unnecessary CT scans being performed for further examination. Accordingly, this report reviews the basic points that should be considered when conducting CT scanning for lung cancer screening purposes.