PLANAR, SPET AND 3-DIMENSIONAL IMMUNOSCINTIGRAPHY OF SUSPECTED RECURRENT COLORECTAL-CANCER USING IN-111-B72.3 (ONCOSCINT CR-OV) - EFFECT OFADMINISTERED ACTIVITY

The monoclonal antibody conjugate In-111-B72.3 was the first such anti body-based radiopharmaceutical for tumour detection to be granted a pr opriety product licence in Europe. However, the optimum activity of In -111 for planar and SPET imaging is yet to be established. A baseline study of 20 patients with suspected recurrent colorectal cancer has be en carried out to assess any effect of administered activity of radion uclide on image quality and tumour detection. Ten patients were admini stered 80 MBq In-111-Oncoscint and 10 patients a larger amount of acti vity, 150 MBq (resulting in effective dose equivalents of 25 and 47 mS v, 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 pa tients magnetic resonance imaging (MRI). No difference in the overall tumour detection was apparent between the two groups and the use of 15 0 MBq In-111 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 interpretat ion of these images. Volume-rendered 3D images offer an attractive met hod of displaying antibody data and require further evaluation.