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78 G. Taino et al.: Radioprotection 2025, 60( 1), 76 – 83

Table 1. Low-dose spiral chest CT scan( LDCT) studies

Period of study

References

have synergistic behavior( Lorenzo-González et al., 2019). Despite this, residential Radon exposure is very often underestimated and usually no risk score for lung cancer includes Radon among the variables under study( Lorenzo-González et al., 2019).

4 Effectiveness of low-dose spiral chest CT in the diagnosis of lung cancer

The results of the American National Lung Screening Trial( NLST) highlighted the favorable prospects for the identification of lung cancer through the use of low-dose chest CT( LDCT) in screening; despite so, the cost-benefit profile of lung cancer screening to date is still a subject of debate in the scientific community( Aberle et al., 2011). The LDCT allows to obtain highly detailed 3D images to identify small tumors a few millimeters wide, with a low exposure to radiation. However, this also highlighted a large amount of indeterminate pulmonary nodules( IPN), 96 % of these being benign in nature and the study failed to show a significant decrease in lung cancer mortality.

The most important studies relating to the use of spiral chest CT in the early diagnosis of lung cancer are collected below( see Table 1).

In all of these studies a significant increase in lung tumors diagnosed at an early stage, therefore surgically treatable, was shown, both compared to studies with chest X-ray and compared to clinical experience. Although CT revealed preclinical tumors, no reduction in lung cancer-specific mortality was observed. On the contrary, the number of false positives was high, with the percentage of surgically treated non-malignant nodules reaching almost 50 %. For these reasons, aspects related to the morbidity and cost-benefit ratio of LDCT screening have been considered more in subsequent studies.

In a major randomized controlled trial published by Bach et al. on JAMA, 2007, over 3,000 smokers were recruited and followed up at the National Cancer Institute in Milan and two other US research centers( Bach et al., 2007). After 5 years, 144 tumors were diagnosed with low-dose computed tomography( LDCT) scan( annual screening)( Bach et al.,

2007), instead of the 44 expected with the mathematical model, and 109 lung resections were performed instead of the 11 expected. Early diagnosis therefore appears to work and has increased operable tumors by 90 %. As regards advanced-stage cancers, however, screening did not significantly increase the number of diagnoses: from the 33 expected cases, 42 were diagnosed. Furthermore, the mortality data failed to confirm the preventive efficacy of lung screening with LDCT: the deaths expected after 5 years were 38.8, against the 38 actually found.

The same study showed however that the survival of patients undergoing resection for stage I lung cancer diagnosed with spiral CT was high. At 5 years, the mortality observed in the subjects of the study mirrored that expected for nonscreened smokers. It can therefore be deduced that radiological screening ensures earlier diagnosis, but fails to change the natural history of the disease, as it seems that at only less aggressive, slow-growing tumors can be diagnosed, and not the more aggressive histotypes, more prone to metastases.

The National Lung Screening Trial( NLST) was the largest study designed to verify whether, in a randomized clinical trial, LCDT screening compared with chest X-ray screening can reduce specific mortality from lung cancer. Conducted between 2002 and 2010, it enrolled 53,454 high-risk individuals, divided into 2 groups, patients undergoing annual control through chest x-ray and Patients undergoing spiral CT annually. With the use of LDCT, a reduction in mortality of 20 % was observed compared to screening conducted with chest X-ray but, at the same time, a rate of false positives of 96.4 % was described, with an overdiagnosis of 78.9 % for bronchoalveolar lung tumors.

In general, in most of the studies that have been conducted, regardless of the increase in the diagnosis and treatment rate of lung cancer during screening, no significant reduction in lung cancer-specific mortality was observed. Furthermore, although the excellent survival of patients with early-stage lung cancer in some studies( particularly in the NLST study) is a strong argument for the LDCT screening, it should be able to intercept the most aggressive forms of cancer, those with the greatest impact on mortality and limiting false positive cases, to be considered useful and effective.