Chest: Oncologic Imaging

One of the classic applications of CT has always been in the detection and staging of thoracic malignancies. Prior studies with single detector CT demonstrated that careful attention to technique with doubling of the frequency of sampling of the scan data volume (4 mm instead of 8 mm intervals) could result in an increase lesion detection rate of just under 10%. Several articles also demonstrated how evaluation of the mediastinum could be done with lower volumes of contrast material. A recent article by Patz Jr et al. even found that nonenhanced helical CT was as good as contrast enhanced CT for the staging of lung cancer in most cases. Our current practice is to always use iodinated contrast for the staging of lung cancer with the volume used being between 100-125 ml depending on whether a chest alone is scanned or if both the chest and liver are scanned as one spiral.

The additional value of MDCT will probably not be in lesion detection but in its ability to scan large volumes in a single breathhold making evaluation of the chest and abdomen a reality for nearly all patients. The speed of acquisition which usually result in a study of under 25 seconds allows evaluation of the liver during the portal phase of enhancement which is typically ideal for detection of liver metastases.

Another advantage of MDCT is the ability to routinely acquire datasets that are of the quality that allow multiplanar and 3D imaging. Both MPR and 3D imaging are of value to the bronchoscopist in difficult cases, to the surgeon in cases of peripheral or central disease or to the radiation oncologist in drawing the proper therapy ports. Johnson et al found the use of interactive 3D volume rendering to be useful in staging lung cancer especially in cases where involvement of the chest wall or vascular invasion is in doubt. Kuriyama et al. infact found that the sensitivity for detection of visceral pleural involvement was 92% for 3D reconstruction and only 17% for axial two-dimensional images. Although to date no published study to our knowledge has compared axial images with MPR/3D for staging of disease such work should be coming soon as MDCT technology becomes more widely available.

Another advantage of MDCT is that the ability to obtain and compare disease progression or regression is optimized by a volume dataset. Determining tumor volume should be more accurate with the new technology as scan will more likely be aligned from study to study making evaluation potentially more accurate. This will be valuable not only on patients with lung cancer but in patients with lymphoma or other malignancies.

A classic oncologic application in both the adult and pediatric patient is to detect the presence of lung metastases. The combination of faster scanning coupled with narrower collimation and closer interscan spacing should make this the study of choice. The improved detection of nodules by MDCT over SDCT has not yet been documented in the literature.

"The results suggest that contrast enhanced thoracic CT through the liver for staging lung cancer rarely changes the tumor stage determined with nonenhanced CT through the adrenal glands does not substantially influence influence management decisions." Lung Cancer Staging and Management: Comparison of Contrast-enhanced and Nonenhanced Helical CT of the Thorax
Patz Jr. EF et al.
Radiology 1999; 212:56-60

Pleural invasion by bronchogenic cancer: assessment with three dimensional helical CT
Kuriyama K et al.
Radiology 1994; 191:365-369

Interactive Three-Dimensional Volume Rendering of Spiral CT Data: Current Applications in the Thorax
Johnson PT et al.
RadioGraphics 1998; 18:165-187