Study Syllabus for Classification of Radiographs of Pneumoconioses
Central Role of Diagnostic Imaging
Role of CT (Part 2)
Screening for Malignancy
The landmark National Lung Cancer Screening Trial demonstrated a 20% reduction in mortality from lung cancer in heavy smokers who underwent annual CT screening for three years, compared with a control group screened with annual chest radiographs [Aberle et al. 2011].
The United States Preventive Services Task Force (USPSTF) therefore recommends annual screening for lung cancer with reduced-dose computed tomography in adults aged 55 to 80 years who have a ≥30 pack-year smoking history and currently smoke or have quit within the past 15 years [Humphrey et al. 2013]. A substantial number of occupational exposures, including asbestos, arsenic, beryllium, cadmium, nickel, radon, and silica, predispose to lung cancer [Gottschall 2002]. The role of CT in screening for occupational-related malignancy in those who do not meet the USPSTF guidelines remains unclear. National Cooperative Cancer Network (NCCN) recommends that individuals with specific occupational exposures who are aged ≥50 and have ≥20 pack years of smoking exposure and have a risk of lung cancer of at least 1.3% over a six year time frame should be eligible for screening [Wood et al. 2015]. Although this recommendation has not yet been adopted by other groups, and calculation of a precise level of risk is problematic, consideration of occupational exposures should be an important part of the shared decision-making process that precedes entry into a lung cancer screening program. Additionally, in patients with occupational exposures, screening CT examinations should be carefully evaluated for evidence of both non-malignant and malignant occupational lung disease.
Identifying Non-Pneumoconiotic Occupational Lung Diseases
As shown in Table 1, non-pneumoconiotic occupational lung diseases are often associated with findings that are subtle, nonspecific or not visible on chest radiographs. For example, many cases of hypersensitivity pneumonitis are characterized by ground glass abnormality, which is easy to identify on HRCT but difficult to see on chest radiograph [Lynch et al. 1992]. Similarly, obliterative bronchiolitis related to inhalational exposure is difficult to identify on chest radiograph. HRCT is thus very helpful in symptomatic patients with known occupational exposures who have normal or near-normal chest radiographs.
Systematic Scoring of Occupational Lung Disease on HRCT
A standardized system for scoring extent of disease on HRCT, very similar to the ILO radiographic classification system, has been published [Kusaka et al. 2005] and is quite widely used [Suganuma et al. 2006; Hering 1992; Hering et al. 2004; Kraus et al. 2009; Tamura et al. 2015]. This system has been shown to be associated with moderate inter-reader and intra-reader agreement for all categories of abnormality except ground glass abnormality [Huuskonen et al. 2001].