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Everything you need to know about Computed Tomography (CT) & CT Scanning

Lung Anatomy Syllabus: Early Lung Cancer Screening

One of the hottest topics in both Radiology as well as Oncology and Epidemiology revolves around the potential role of CT in screening high-risk patients (smokers) for lung cancer. With an estimated 160,000 deaths in 1998 from lung cancer just in the United States it is not suprising that lung cancer continues to remain a significant health hazard today. The goal of early lung cancer screening is to detect cancer at a stage when it is still potentially curable. In a study from Henschke et al. a total of 1000 symptom free volunteers with at least 10 pack years of cigarette smoking were screened with both CT and chest x-ray. CT detected 27 cancers and chest x-rays but 7. What was most important however was that in 23 of the patients disease was stage I and that of the 27, 26 were resectable. Similar results have been shown in data from Sone et al. where a total of 5,483 patients were studied with both chest x-rays and latter low dose helical CT. In this study the lung cancer detection rate with CT was 0.48%, significantly higher than the 0.03-0.05% for standard mass assessments (chest x-rays) done previously in the same area."

Although both of these articles and other reports have been promising a recent article by Patz JR et al. reminds us that lesion detection alone may not effect the final outcome. In a review of 510 with pathologic stage IA (T1N0M0) there was no statistical relationship between tumor size and survival. The author noted that "these data caution that improved small nodule detection with screening CT may not significantly improve lung cancer mortality." The author suggests that an appropriate randomized trial will be needed to prove the value of screening CT.

Although there is still some controversy as to the use of CT to screen all smokers in the United States today it is not suprising that MDCT would be the ideal study technique. A screening study requires rapid patient throughput as well as a study which minimizes the need for patient inconvenience (especially if follow-up studies are needed). MDCT provides this with a scan that will take in the 10-15 second time frame depending on the scan protocol selected. The use of a true volume acquisition also provides the opportunity for new technologies to visualize the data. Although prior studies have shown that cine viewing is preferred to film based viewing (and mandatory in a screening study where the reimbursements are lower and so the cost of study needs to be minimized) videotaping may be a low cost option.

3D volume displays with either volume rendering technique or maximum intensity projection (MIP) may prove to be more accurate than even cine displays especially when trying to distinguish small nodules from vessels. With an interactive volume display it is possible to follow the branching of a vessel in three dimensions. The 3D volume display is also valuable in the evaluation of the hilar regions. Volume displays may also prove to be a solution to the large number of slices that can be generated with MDCT. Instead of looking at 200-500 individual slices the entire volume may be displayed and viewed in a volume format. It is our belief that the future of image display will be volumes.

"Low dose CT can greatly improve the likelihood of detection of small non-calcified nodules, and thus of lung cancer at an earlier and potentially more curable stage."

Early Lung Cancer Action Project: Overall Design and Findings from Baseline Screening
Henschke CI et al.
Lancet 1999; 354:99-105

© 1999-2020 Elliot K. Fishman, MD, FACR. All rights reserved.