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Theoretical Limitations in the Immunodiagnostic Imaging of Cancer with Computed Tomography and Nuclear Scanning¹

Department of Radiology, The George Washington University Medical Center, Washington, D. C. 20037 [S.D.R., D.J.G.], and The Laboratory of Immunodiagnosis, National Cancer Institute, NIH, Bethesda, Maryland 20205 [K.R.M.]

In order to help assess the feasibility of using immunologically tagged agents to render tumors detectable with current computed tomographic and nuclear scanners, mathematical formulations were developed to determine the theoretical limits of tumor detection relative to size and depth of the lesions.

The results of our analysis suggest that visualization with computed tomography of a tiny tumor (1 sq mm, cross-sectional area) would require binding in the order of 2 x 10⁵ iodine atoms/antigenic site, while imaging of a very large (900-sq mm) tumor would require approximately 10⁴ atoms/site. Very low energy scanners might reduce these discouraging estimates by an order of 10².

The immunological imaging of tumors with nuclear scanning appears quite feasible from our formulations, as has been demonstrated by others clinically. Small (1-sq cm) and deep (5-cm) tumors appear detectable with uptake ratios of the order of 5 or higher, which seem to be attainable currently. Smaller and deeper tumors require much higher uptake ratios to be detected.

¹ Presented at the UICC Workshop on Radioimmunodetection of Cancer, July 19 to 21, 1979, Lexington, Ky.