Assessment and significance of mediastinal bulk in Hodgkin's disease: comparison between computed tomography and chest radiography.

PURPOSE: In Hodgkin's disease (HD), mediastinal bulk is currently defined from chest radiograph (CXR) measurements as a ratio of the maximum transverse mass diameter to the internal thoracic diameter at T5/6 level > or = 0.33. We evaluated how computed tomographic (CT) measurements of bulk correspond to those obtained from the CXR and correlated nodal mass long axis diameter with freedom from progression. METHODS: Ninety-five adult patients who had a CXR thoracic ratio of greater than 0.3 and a CT scan within 28 days of the CXR were included in the study, provided that both investigations were performed before the start of treatment. Measurements of the widest mediastinal diameter and internal thoracic diameter were made on both CXR and CT scan. The thoracic ratio (TR) was calculated for each modality and compared using paired t tests. The longest diameter of the largest individual nodal mass (LIM(CT)) was also measured from the CT and correlated with freedom from progression using Cox regression. RESULTS: There was excellent correlation between CT and CXR for measurement of TR, with TR(CT) greater than TR(CXR) (mean difference of 2%). A TR(CT) of 0. 35 was found to be equivalent to a TR(CXR) of 0.33. No single measurement of nodal size correlated with the current definition of bulk. However LIM(CT) greater than 10 cm did correlate with increased risk of progressive HD (P =.03), even after adjustment for other prognostic variables (chemotherapy regimen and Hasenclever Prognostic Index). CONCLUSION: Excellent correlation was observed between assessment of TR by CXR and CT scan. The longest diameter of the LIM(CT) greater than 10 cm was found to be associated with an increased risk of disease progression.