Performance of chest radiograph and CT scan for lung cancer screening in asbestos-exposed workers

Our plain-English summary of Performance of chest radiograph and CT scan for lung cancer screening in asbestos-exposed workers, by B. Clin, F. Morlais, L. Guittet, et al (Occupational and Environmental Medicine, 2009).

The study

• Authors: B. Clin, F. Morlais, L. Guittet, A. Gislard, M.F. Marquignon, C. Paris, J.F. Caillard, G. Launoy, M. Letourneux
• Journal: Occupational and Environmental Medicine
• Published: 2009;66(8):529-34
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: The aim was to compare, in a cohort of asbestos-exposed workers, the sensitivity and the specificity of low-radiation helical chest CT scan with chest radiograph for the biennial screening of bronchopulmonary cancer, according to the size of detected nodules.

Material And Methods: The screening procedure consisted of biennial chest radiograph and monodetector chest CT scan, given to 972 individuals who had been highly exposed to asbestos. A total of 2555 screening procedures were performed. The study focuses on the 1230 screening procedures for which a 2-year follow-up period was available.

Results: Twenty-four cases of bronchopulmonary cancer were diagnosed. CT scan detected 20 cancers, 12 of which had not been detected by chest radiograph. Sensitivity of chest radiograph and CT scan were, respectively, 33% and 83%, lesions measuring over 2 mm in diameter being considered as suspect. The specificity of chest radiograph and CT scan were, respectively, 95% and 78%. Calculation of the differential false positive/true positive (FP/TP) ratio and the receiver operating characteristic curve, performed for both chest radiograph and CT scan, facilitated the determination of the best possible compromise between specificity and sensitivity, according to the diameter threshold applied for considering a nodule as suspect.

Conclusions: Although this study confirms the superior sensitivity of chest CT scan compared with conventional chest radiograph, the associated loss in specificity leads to a recommended diameter of 5 mm as the threshold for considering non-calcified lesions as "suspect", for the surveillance of asbestos-exposed individuals.

In plain English

This study compared low-dose chest CT scans with chest X-rays for finding lung (bronchopulmonary) cancer in 972 people with high occupational asbestos exposure in Normandy, France. Most had worked in asbestos-based textiles and friction lining, metallurgy or naval construction. Of 2555 screenings done every two years between 2000 and 2006, the 1230 with two years of follow-up were analysed. Twenty-four cancers were found: 20 by screening and 4 with symptoms after both tests were negative. CT found 12 that X-ray missed. Counting nodules over 2 mm as suspect, CT sensitivity was 83% and specificity 78%, against 33% and 95% for X-ray. At that cutoff, CT gave an estimated 17.58 extra false positives per extra cancer found (95% confidence interval 9.77 to 31.64). At 5 mm, CT sensitivity was 0.79 and specificity 0.92, with 6.09 extra false positives per extra cancer (95% confidence interval 3.09 to 11.99). Five pleural mesotheliomas were detected. Under their study conditions, the authors recommended considering CT-detected non-calcified nodules suspect when over 5 mm in diameter. They noted that this non-randomised study cannot show whether screening reduces lung cancer deaths.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Non-randomised screening study in a cohort, comparing biennial chest radiograph with low-dose single-slice (monodetector) helical chest CT scan in the same people
• Who was studied: 972 individuals (920 men, 52 women), aged 50 to 75 at first examination, attending post-exposure surveillance at university hospital occupational health departments in Caen, Rouen and Le Havre (Normandy, France), examined 1 January 2000 to 31 December 2006. 2555 screening procedures were performed; the analysis covered the 1230 with a 2-year follow-up. 68% were smokers or former smokers.
• Exposure: Occupational asbestos exposure judged 'important': confirmed, high and continued exposure for more than 1 year, or confirmed, high discontinued exposure for 10 years or more. Jobs were dominated by asbestos-based textiles and friction lining, metallurgy and naval construction. Fiber types are not specified.
• Main results:
  • 24 patients in the cohort had bronchopulmonary cancer. 20 clinically asymptomatic cancers were detected by screening (13 at baseline, 5 at the second and 2 at the third biennial screening).
  • 4 further cancers (interval cancers) appeared with symptoms within 2 years of a screening in which both tests were negative.
  • CT scan detected 20 cancers, 12 of which had not been detected by chest radiograph.
  • One or more suspect nodules were found by CT in 23% of screening participants, versus roughly 5% by chest radiograph.
  • With nodules over 2 mm counted as suspect, sensitivity was 83.3% for CT and 33.3% for chest radiograph.
  • At the 2 mm threshold, specificity was 95% for chest radiograph and 78% for CT.
  • At the 2 mm threshold, CT was 2.5 times more sensitive than chest radiograph (ratio of sensitivities 2.50, 95% CI 1.46 to 4.28). It generated 4.77 times more false positives (ratio 4.77, 95% CI 3.63 to 6.26). The estimated ratio was 17.58 extra CT false positives per extra cancer detected (95% CI 9.77 to 31.64).
  • At a 5 mm threshold, CT had a sensitivity of 0.79 and a specificity of 0.92, with three times more false positives than chest radiograph. The estimated ratio was 6.09 extra false positives per extra cancer detected (95% CI 3.09 to 11.99).
  • The detection rate of bronchopulmonary cancer was 0.82% for chest radiograph and 2.16% for chest CT scan.
  • 11 of the screen-detected bronchopulmonary cancers were stage I (reported as 57.14%).
  • Five pleural mesotheliomas were detected during the study. One asymptomatic case was found within the screening protocol after a slight pleural effusion was detected. Four presented with symptoms after a negative screening result.
• The authors' conclusion: The authors concluded that CT's better sensitivity comes with a loss in specificity. Under their study conditions, they recommended a diameter threshold of over 5 mm for considering CT-detected non-calcified nodules as suspect in the biennial surveillance of asbestos-exposed individuals.
• Limitations the authors state:
  • Disease status could not be confirmed for people with normal results, so sensitivity and specificity were estimated from interval cancers. Missed slow-growing cancers could make sensitivity look higher than it is, and fast-growing new cancers could make it look lower.
  • The relatively small study population reduced statistical power and widened confidence intervals.
  • The screening procedure, not the individual, was the unit of analysis. Some individuals were therefore counted more than once, which may cause a non-independence effect.
  • A differential verification bias could be raised, because nodules seen on chest radiograph but not confirmed by CT were not followed by CT. The authors considered this bias improbable.
  • The single-slice (monoslice) CT scanners used may appear somewhat obsolete given progress in imaging.
  • The lower proportion of stage I cancers than in other studies may result from the biennial (rather than annual) screening frequency.
  • As a non-randomised study, it cannot show whether screening reduces deaths from bronchopulmonary cancer.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Chest X-Ray, CT Scan, Low-Dose CT Screening.

Related studies

• Chest CT scan screening for lung cancer in asbestos occupational exposure: a systematic review and meta-analysis — M. Ollier, A. Chamoux, et al. (2014)
• CT scan screening is associated with increased distress among subjects of the APExS — C. Paris, M. Maurel, et al. (2010)
• Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis? — B. Clin, C. Paris, et al. (2011)
• Findings from high resolution computed tomography of the lung and pleura of symptom free workers exposed to amosite who had normal chest radiographs and pulmonary function tests — S. Neri, A. Antonelli, et al. (1994)
• Antemortem diagnosis of asbestosis by screening chest radiograph correlated with postmortem histologic features of asbestosis: a study of 273 cases — K.N. Mizell, C.G. Morris, et al. (2009)
• Comparison of chest digital tomosynthesis and chest radiography for detection of asbestos-related pleuropulmonary disease — G. Lee, Y.J. Jeong, et al. (2013)

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