SEMIQUANTITATIVE SPECT TUMOR UPTAKE OF TC-99M-LABELED ANTI-CEA MONOCLONAL-ANTIBODY IN COLORECTAL TUMOR

Technetium-99m-BW431/26 images were compared to images of resected tum or specimens to evaluate the efficacy and accuracy of SPECT imaging of colorectal carcinoma. Methods: Immunoscintigraphy with Tc-99m-BW431/2 6 was performed on seven patients with colorectal carcinoma and one pa tient with a benign colorectal tumor. Accumulation of Tc-99m-BW431/26 in the tumor was expressed as the tumor-to-normal tissue count ratio ( SPECT T/N ratio) calculated by a region of interest method on the SPEC T images obtained 24 hr after administration of Tc-99m-BW431/26. All p atients underwent resection of the tumor immediately after 24-hr imagi ng, and the radioactivity in tumor specimen and normal tissue was meas ured to calculate the tissue T/N ratio. Results: SPECT demonstrated de finite increased tracer uptake by the tumor in all colorectal cancer p atients. The benign lesion showed tracer uptake to a lesser extent. SP ECT, however, failed to visualize a 10-mm lesion in a patient with fam ilial adenomatous polyposis despite a tissue T/N ratio of 4.8, while a utoradiography showed radioactivity uptake in the polyps. Conclusion: Although SPECT has limitations in detecting small lesions because of i ts limited spatial resolution, T/N ratios could be measured exactly by SPECT if the lesion is of a certain volume. SPECT imaging with Tc-99m -BW431/26 can precisely evaluate tracer uptake in tumors and predict t he efficacy of radioimmunotherapy in patients with colorectal cancer.