Planar, SPET and three-dimensional immunoscintigraphy of suspected recurrent colorectal cancer using 111In-B72.3 (Oncoscint CR-OV): effect of administered activity.

The monoclonal antibody conjugate 111In-B72.3 was the first such antibody-based radiopharmaceutical for tumour detection to be granted a propriety product licence in Europe. However, the optimum activity of 111In for planar and SPET imaging is yet to be established. A baseline study of 20 patients with suspected recurrent colorectal cancer has been carried out to assess any effect of administered activity of radionuclide on image quality and tumour detection. Ten patients were administered 80 MBq 111In-Oncoscint and 10 patients a larger amount of activity, 150 MBq (resulting in effective dose equivalents of 25 and 47 mSv, respectively). Planar, orthogonal SPET and 3D volume-rendered SPET images were obtained and the image quality was assessed. The clinical results were compared with computed tomography (CT) and in selected patients magnetic resonance imaging (MRI). No difference in the overall tumour detection was apparent between the two groups and the use of 150 MBq 111In for planar imaging alone cannot be justified. Orthogonal and 3D SPET imaging was helpful in confirming sites of uptake and may justify the use of the higher administered amount of activity; however, false-positive results raise the need for caution in the interpretation of these images. Volume-rendered 3D images offer an attractive method of displaying antibody data and require further evaluation.