Workshop on the Chest X-ray Film as an Epidemiologic Tool

Abstract

The prevention of occupational lung diseases requires specific and sensitive indicators of an adverse biologic response that can be related to accurate environmental determinations of harmful inhalants. If this can be accomplished, dose-response relationships and threshold limits of exposure below which the undesirable tissue response does not occur can be established. Just as standardization of methodology has been essential in the use of questionnaires and pulmonary function in epidemiologic investigations of chronic obstructive pulmonary disease (COPD), the need for sensitive and exact techniques was recognized even earlier in evaluating pneumoconioses; in 1930 the International Labor Organization (ILO) proposed the first classification of radiographic appearances in the mineral dust diseases, primarily silicosis. Used initially for compensation purposes, revision of the classification in 1950 was based on epidemiologic principles and intended for use in population studies. It became descriptive rather than interpretive, and compensation was no longer considered. Standard films were added in 1958, and in 1968 a new classification had been developed that applied to all pneumoconioses (including asbestosis); small opacities were now divided into “rounded” and “irregular,” and the scale was expanded to 12 categories, bringing it closer to a continuum. Further minor changes in 1971 have resulted in the currently used form of the classification, termed the ILO U/C International Classification of Radiographs of Pneumoconioses.1ILO U/C International Classification of Radiographs of Pneumoconioses, 1971 (No. 22, revised). Occupational Safety and Health Series. International Labour Office, Geneva1972Google Scholar A recent workshop has addressed itself to a review of problems in the use of the ILO U/C classification, emphasizing correlation of radiographic changes with indices of dust exposure, lung pathology and lung function, and technical and methodologic considerations.2Report of Workshop on the Chest X-Ray as an Epidemiologic Tool, March 25-26, 1974, New Orleans, sponsored by Division of Lung Diseases, NHLI. Arch Environ Health (in press)Google Scholar An international group of experts participated in the workshop and, in addition to the above discussions, produced several conclusions and recommendations. The advantages of the ILO U/C Classification were reaffirmed; but concern about interobserver variability in grading small opacities, the development of fully adequate standardized techniques for production of a chest x-ray film, and the interpretation or significance of small irregular opacities, particularly in coal workers’ pneumoconiosis (CWP), cannot be eliminated. However, it has been demonstrated in many, if not all, types of dust exposure that the classification measures the extent of the dust-related disease and correlates well with assessments of pathologic and functional changes. In CWP, the extent of radiographic changes correlates with total dust retained in the lungs (and dust exposure?), but correlates less well with the degree of physiologic abnormalities. In the manufacture of products containing asbestos and silica, dose-response relationships have been demonstrated, with lung function and x-ray changes being equally sensitive in detecting the adverse effects of the dust exposure. When assessing progression of disease in longitudinal studies, paired films should be used by both independent randomized and side-by-side methods. In epidemiologic studies, at least three readers should be used to minimize observer variability, and their comparability should be established initially and checked at regular intervals. Standard reference films should be used continuously by all readers, chest films of unexposed workers should be included for purposes of control, and a proportion of films should be fed back to the reader periodically to check repeatability. While the classification can be used to set safe standards for inorganic dust levels, the use of the chest x-ray film as an epidemiologic tool in the organic dust diseases, other nonoccupational diffuse pulmonary infiltrative disorders (eg, sarcoidosis), and COPD has not been established. It was suggested that high priority should be given to the precise definition of a “good film” and that illustrative chest x-ray films should be provided to insure film quality. Automated digital and optical methods of film reading now being developed are likely to minimize observer variability and reduce the magnitude of reading loads. These methods can be used to assess film quality and to discount variations in exposure techniques and should be ideally suited to determine progression of disease in paired films. It seems generally accepted that the chest x-ray film is the most accurate antemortem indicator of a dust effect in the lungs. Through the efforts of many of the participants of this workshop, the development and improvement of an international classification has provided investigators of occupational lung disease with a powerful tool that, together with other methods of measuring biologic responses and characterizing the environment, should help in reaching the goal of eliminating work-related lung disease.