Value of whole body 123I scan for detection of metastasis in patients with well-differentiated thyroid carcinoma

To evaluate the utility of 123I whole body scan for detection of metastasis in patients with well-differentiated thyroid carcinoma, post-therapy whole body 131I images in 55 cases were compared with pre-therapy 123I images using diagnostic dose (74 MBq). The post-therapy studies were performed 7 days after administration of therapeutic doses (3.33-7.77 GBq) of 131I. The pre-therapy scans showed 30 lesions (71.4%) of 42 lesions which were shown by 131I post-therapy scans. The diagnostic accuracy of 123I whole body scans was considered to be nearly the same as the images obtained by 131I using diagnostic dose. 123I has short-life and an optimum gamma ray energy for scintigraphy. It makes radiation dose to patients lower than that of 131I. Therefore, we recommend pre-therapy 131I image using diagnostic dose is replaced by 123I image. (author)