UK Naval Dockyards Asbestosis Study: radiological methods in the surveillance of workers exposed to asbestos

Our plain-English summary of UK Naval Dockyards Asbestosis Study: radiological methods in the surveillance of workers exposed to asbestos, by G. Sheers, C.E. Rossiter, J.C. Gilson, et al (British Journal of Industrial Medicine, 1978).

The study

• Authors: G. Sheers, C.E. Rossiter, J.C. Gilson, F.A. Mackenzie
• Journal: British Journal of Industrial Medicine
• Published: 1978;35(3):195-203
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 002151).

Abstract

ABSTRACT In a survey of the effects of exposure to asbestos in the UK Naval Dockyards, small- and large-film chest radiographs of 674 men have been examined. These films have been read under survey conditions by two readers using a simple screening classification, and also in a controlled trial by five readers using the full ILO U/C classification. Comparison between the reading methods showed a deficiency, independent of the size of film, of at least 30% in the detection of asbestos-related radiographic abnormalities when the screening classification was used. For adequate diagnostic sensitivity the ILO U/C classification appears to be essential. There was a deficiency of 43% in significant abnormalities observed by a majority of readers in the small films when directly compared with large film readings. This deficiency could be reduced to 7% by using readings of the small films at any level of abnormality by any of the five readers. When the ILO U/C readings were related to the clinical diagnoses, the only abnormality missed was a small pleural plaque. Films with previously agreed coding were inserted at intervals during the reading trial and helped to maintain the consistency of reading. Right oblique views were taken for 1884 men, in addition to the full-sized postero-anterior view, but the contribution provided by this view proved insufficient to justify its use in large surveys. The cost of a survey when small films are used as a screening method is reduced to between one-third and one-half of the cost when large films are used, assuming that the abnormality rate is not more than 5%. However, this cost advantage for small films is likely to be overtaken by the development of automatic large-film units. The radiation dose when small films are used is increased by a factor of about 20, but is within the prescribed safety level. It is concluded that at least three readers should be involved, using the full ILO U/C classification. Small films may be of particular use in a large-scale survey, in which the abnormality rate is expected to be low, and which might otherwise be too expensive. A sensitive reading method and a high standard of film quality are essential factors in the use of this technique.

In plain English

This study, from an asbestos survey of male workers in the four main UK naval dockyards, compared ways of taking and reading chest X-rays. Of 674 men X-rayed on both small (100 mm) and large films, five readers using the ILO U/C classification judged 125 large films positive at a standard level. Small films read the same strict way picked up 71 of these. Counting any abnormality noted by any reader picked up 116, with 22 of 549 false positives. The simpler screening classification left 36% of these positive cases read as normal on small films, and 30% even on large films. Oblique views for 1884 men were the only sign of abnormality in seven cases, all pleural thickening. Small films gave an average skin dose of 220 mrad, against 11 mrad for large films. The authors concluded that at least three readers should use the full ILO U/C classification, and oblique views are not justified in large surveys. They judged small films of particular use in large, low-abnormality surveys that might otherwise be too expensive, with sensitive reading and high film quality essential.

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: Methods study within a workplace X-ray survey: a controlled film-reading trial comparing reading methods (screening classification vs full ILO U/C classification), film sizes (small 100 mm photofluorographs vs large films), and an extra oblique view, with costs and radiation dose also assessed
• Who was studied: All male workers in the four main UK naval dockyards. The total population was 36714, of whom 28971 were examined. A stratified sample of 2040 men was weighted toward heavier exposure, and 1902 of them were examined on full-sized films. Both large and small films were available for 674 men. Oblique views were assessed for 1884 men.
• Exposure: Asbestos exposure in naval dockyard occupations; no fiber types are named. The sample included all registered asbestos workers of any age. From other jobs it included men aged 50-59: about one in three in jobs with intermittent exposure and one in 30 in jobs with lesser or negligible risks.
• Main results:
  • Of the 125 men whose large films were positive at the standard level (agreed by at least three of five readers), small films read to the same standard were positive for 71. The authors described this as a serious deficiency in the sensitivity of the small films.
  • When any abnormality recorded by any of the five readers on the small films was counted, small films were positive for 116 of the 125 standard-level large-film positives (92.8%). This would mean a recall rate of 20% and a false positive rate of 22 out of 549 (4%).
  • Under the simple screening classification read by two readers, 36% of men with positive large films were screened as normal on small films. On the large films themselves, 30% were screened as normal.
  • Among 1884 oblique views, the oblique view was the only indicator of abnormality in seven cases (0.4% of all oblique views), and all seven were pleural thickening.
  • Compared with clinical findings, one pleural plaque was read as normal in all ILO U/C readings, and all missed cases were small pleural plaques. By comparison, 25 pleural abnormalities were missed on the small films in the screening procedure: one was diffuse pleural thickening and the others were pleural plaques.
  • Measured in 10 adult males for each technique, the average skin dose was 220 mrad (range 95-315 mrad) for the 100 mm small film. For the standard postero-anterior large film it was 11 mrad (range 7-17 mrad).
  • Assuming about £1 per small film examination, the estimated survey cost was approximately £85 000 for large films and £30 000 for small films. Allowing for recall examinations reduced the difference to £46 500.
• The authors' conclusion: The authors concluded that at least three readers using the full ILO U/C classification should be involved. They found oblique views useful for individuals but not justified in large-scale surveys. They judged that small films may be of particular use in a large-scale survey where the abnormality rate is expected to be low and which might otherwise be too expensive. They called a sensitive reading method and a high standard of film quality essential factors in using this technique.
• Limitations the authors state:
  • The authors stated that observer variation remained a considerable problem, with inter-observer differences similar to earlier trials.
  • The authors stated that film quality could have been improved: the large films were not as good as more modern equipment could achieve, and small films often had positioning faults.
  • The authors stated that the sensitivity reached with small films by counting any reading by any reader is unlikely to suit comparison with other studies, and should be questioned for detecting individual abnormalities of possible clinical significance.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, The Navy.

Medical terms in this study, explained in our Lexicon: Chest X-Ray, Pleural Plaques.

Related studies

• UK Naval Dockyards asbestosis study: survey of the sample population aged 50-59 years — C.E. Rossiter, P.G. Harries (1979)
• Royal Naval dockyards asbestosis research project: nine-year follow-up study of men exposed to asbestos in Devonport Dockyard — C.E. Rossiter, J.R. Heath, et al. (1980)
• The health of welders in naval dockyards. The risk of asbestos-related diseases occurring in welders — G.H. McMillan (1983)
• Protection of dockyard workers against asbestosis — P.G. Harries (1970)
• Correlation between fibre content of the lungs and disease in naval dockyard workers — J.C. Wagner, C.B. Moncrieff, et al. (1986)
• Navy Asbestos Medical Surveillance Program 1990-1999: demographic features and trends in abnormal radiographic findings — D.M. Dell, B.K. Bohnker, et al. (2006)

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