Low-dose CT for lung cancer screening: position paper from the Italian college of thoracic radiology

Abstract

Smoking is the main risk factor for lung cancer (LC), which is the leading cause of cancer-related death worldwide. Independent randomized controlled trials, governmental and inter-governmental task forces, and meta-analyses established that LC screening (LCS) with chest low dose computed tomography (LDCT) decreases the mortality of LC in smokers and former smokers, compared to no-screening, especially in women. Accordingly, several Italian initiatives are offering LCS by LDCT and smoking cessation to about 10,000 high-risk subjects, supported by Private or Public Health Institutions, envisaging a possible population-based screening program. Because LDCT is the backbone of LCS, Italian radiologists with LCS expertise are presenting this position paper that encompasses recommendations for LDCT scan protocol and its reading. Moreover, fundamentals for classification of lung nodules and other findings at LDCT test are detailed along with international guidelines, from the European Society of Thoracic Imaging, the British Thoracic Society, and the American College of Radiology, for their reporting and management in LCS. The Italian College of Thoracic Radiologists produced this document to provide the basics for radiologists who plan to set up or to be involved in LCS, thus fostering homogenous evidence-based approach to the LDCT test over the Italian territory and warrant comparison and analyses throughout National and International practices.

Keywords: Computed tomography; Computer assisted diagnosis; Early diagnosis; Lung cancer; Lung nodule; Screening.

Fig. 1

A–D. Measurement of a solid nodule with histologic diagnosis of adenocarcinoma in the right upper lobe and its growth. Axial CT image showing a solid nodule in the right upper lobe. Two examples of measurement are displayed: A manual caliper (maximum diameter 7 mm, orthogonal diameter 3.4 mm, mean diameter 5.2 mm) and B semi-automatic volume segmentation (B: 108 mm³). The follow-up scan shows growth of the solid nodule compared to first detection, which is below the minimum threshold of 2 mm by manual caliper (C: 7.5 × 4.3 mm, mean diameter 5.9 mm) and above the minimum threshold of 25% by volume segmentation (160 mm³): such discrepancy reflects into divergent classification as stable by manual caliper and grown by volume segmentation, for this solid nodule that was diagnosed adenocarcinoma. Furthermore, the longitudinal calculation of growth rate shows different estimate of volume doubling time by manual caliper (445 days) or volume segmentation (236 days)

Fig. 2

A–B. Measurement of a part-solid nodule in the left upper lobe and its growth. Axial CT image showing a part-solid nodule in the left upper lobe. The size of the solid component by manual caliper at first detection (A: maximum diameter 3.7 mm, orthogonal diameter 1.3 mm, mean diameter 2.5 mm) is thereafter confidently increased at follow up scan (B: 7.9 × 6.3 mm, mean diameter 7.1 mm). The variable and limited density difference between solid component and non-solid component represents a factor for variability of semi-automated volume segmentation. Moreover, the figure shows small vessels abutting the surface of the solid component, that is one common factor that further hampers the use of volume segmentation of solid core in part-solid nodules

Fig. 3

A–B. Measurement of a non-solid nodule (ground glass opacity) in the apical segment of the right lower lobe and its growth. Axial CT image showing a non-solid nodule in apical segment of the right lower lobe. The measurement by manual caliper at first detection (maximum diameter 14.3 mm, orthogonal diameter 12.4 mm, mean diameter 13.4 mm) and follow up scan (B: 16.5 × 16.5 mm, mean diameter 16.5 mm). The variable and limited density difference between the non-solid nodule and the surrounding parenchyma represents a factor for variability of semi-automated volume segmentation

Fig. 4

A–D. Collateral (smoking-related) findings in screening LDCT. Calcifications of the coronary arteries. Axial CT images at the level of the left main coronary artery showing different degrees of coronary artery calcification (CAC): absent = 0 (A), mild = 1 (B), moderate = 2 (C) and severe = 3 (D). According to the scale proposed by Chiles et al. [67], isolated flecks correspond to a mild degree (B), continuous calcification along the vessel correspond a severe degree (D)

Fig. 5

A–D. Collateral (smoking-related) findings in screening LDCT. Quantification of pulmonary emphysema with application of the 950HU density mask. Pulmonary emphysema quantified by density mask with segmentation of lung areas with density lower than − 950 HU. The example shows the step-wise process of segmentation of lung parenchyma (A: native image; B: extraction of lung volume) and subsequent quantitation of emphysema extent represented as low attenuation area (LAA) with density below − 950 HU, as represented by green overlay (C). The density histogram (D) shows the distribution of density across the lung volume, and allows to quantify the proportion of LAA below -950 HU as relative extent compared to the overall lung volume (E), namely 11% in this example (specific lobar quantitation is also provided)

Fig. 6

A–D. Collateral (smoking-related) findings in screening LDCT:interstitial lung abnormalities with varying extent and morphology.Axial CT image at the level of mid-lower chest showing different patterns of interstitial lung abnormalities with varying severity: A minor reticulation in right lateral sulcus; B reticulation with signs of bronchiolar traction in the lower lobes; C ground-glass opacity with mild extent in the lower lobes; D ground-glass opacity with extensive distribution in the lower lobes, associated with minimal areas of parenchymal sparing with lobular distribution. These findings variably represent smoking related disease, with either reversible or irreversible behaviour worth of multidisciplinary discussion