Comparison of response evaluation in small cell lung cancer using computerized tomography and chest radiography

Abstract

The percentage of patients achieving a complete response (CR) to therapy is often used as a measure of treatment efficacy in SCLC. Chest radiographs are difficult to evaluate following therapy and differences in reported response rates may be due to interobserver variation. CT scans of the thorax are more costly and are not as easily obtained as routine studies. We wanted to determine whether the measurability rate and interobserver agreement on response was superior when using CT scans, compared to chest radiographs alone. Fourteen radiologists with expertise in CT imaging of the thorax, reviewed 15 cases of SCLC pre- and post-chemotherapy (210 observations). In the first session, reviewers were required to measure or evaluate all possible lesions on the plain chest radiograph done at pre- and post-treatment. In the second session, accompanying CT scans were provided in order to make the same assessments. The number of instances in which neoplastic disease was measurable in two cross-sectional diameters on pretreatment films was 164 (79%) on chest radiographs and 202 (97%) on CT scans. Interobserver agreement was assessed by comparing tumour measurements, as well as reports of complete disappearance of tumour (CR) among the 15 observers. The rate of CR ranged from 0 to 87% with the use of the chest radiograph, and from 0 to 95% using the CT scan. Usually after viewing the CT scan, readers changed their opinion as to whether CR had actually occurred. For example, in one case, 87% of readers judged response to therapy as a CR based on chest radiograph; upon reevaluation with a CT scan this figure decreased to 15%. Agreement as to response was better on review of the CT scans, compared to the chest radiograph in all but two cases. It is therefore recommended that pre- and post-treatment CT scans, and not just chest radiographs, be used for assessment of response to therapy.