Correspondence

Staging of Lung Cancer with Integrated PET–CT

N Engl J Med 2004; 350:86-87January 1, 2004

Article

To the Editor:

Lardinois et al. (June 19 issue)1 state that tumor and nodal staging is more accurate with integrated positron-emission tomography and computed tomography (PET–CT) than with CT or PET alone. In their study, PET alone was visually correlated with CT, which is the standard of practice for reading PET scans. However, Lardinois et al. used non–diagnostic-quality, non–contrast-enhanced CT, which is not the type generally used for correlation at most PET centers. It is not surprising that PET–CT outperformed CT alone in tumor staging, since the tumor stage was determined with the use of non–diagnostic-quality CT. Newer-generation PET scanners also have the ability to overlay transmission and emission images, providing a relatively detailed view of the anatomy of the tracheobronchial tree and improving nodal localization. In addition, it is likely that nodal staging with PET alone and visual correlation would have been more accurate if diagnostic-quality, contrast-enhanced CT and transmission images had been used. In the study by Lardinois et al., the diagnostic accuracy of nodal staging worsened with visual correlation (as shown in Table 3 of their article). Perhaps this reflects the difficulty of identifying lymph nodes with non–diagnostic-quality, non–contrast-enhanced CT.

Glenn P. Ollenberger, M.D., Ph.D.
University of British Columbia, Vancouver, BC V6T 1Z2, Canada
gollenberger@telus.net

1 References

1. 1

   Lardinois D, Weder W, Hany TF, et al. Staging of non-small-cell lung cancer with integrated PET and CT. N Engl J Med 2003;348:2500-2507
   Full Text | Web of Science | Medline

Author/Editor Response

The CT scans used in our study were of diagnostic quality. In all the patients, conventional, enhanced CT was performed before integrated PET–CT scanning. Whenever there was a critical advantage associated with PET–CT, we also had the enhanced CT scans, which were not helpful diagnostically. The enhanced CT scans were not included in the statistical analysis because they were obtained at several institutions and with different protocols.

The problem encountered when juxtaposed PET and CT images, rather than “fused” images, are read is that there is not enough anatomical information in PET images to allow mental superimposition of observed lesions onto the corresponding CT sections. PET transmission scans are anatomically imprecise, and with these scans, chest-wall infiltration cannot be diagnosed. Hence, the difference in the results between integrated PET–CT and visual correlation with PET alone and CT alone is due not to the quality of the image in the CT scans used in our study but rather to the difficulties of mentally superimposing images accurately, when the anatomical landmarks are virtually absent on one image. Several groups have confirmed our results, reporting that PET–CT (when CT is performed with or without contrast material) is more accurate in staging than conventional imaging methods.1-3

Walter Weder, M.D.
Gustav K. von Schulthess, M.D., Ph.D.
Hans C. Steinert, M.D.
University Hospital of Zurich, 8091 Zurich, Switzerland
hans.steinert@usz.ch

3 References

1. 1

   Bar-Shalom R, Yefremov N, Guralnik L, et al. Clinical performance of PET/CT in evaluation of cancer: additional value for diagnostic imaging and patient management. J Nucl Med 2003;44:1200-1209
   Web of Science | Medline

2. 2

   Antoch G, Stattaus J, Nemat AT, et al. Non-small cell lung cancer: dual-modality PET/CT in preoperative staging. Radiology 2003;229:526-533
   CrossRef | Web of Science | Medline

3. 3

   Cohade C, Osman M, Leal J, Wahl RL. Direct comparison of ¹⁸F-FDG PET and PET/CT in patients with colorectal carcinoma. J Nucl Med 2003;44:1797-1803
   Web of Science | Medline

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