Camprison of Diagnostic and Therapeutic scans in Patients with Differentiated Thyroid Cancer / 대한내분비학회지

ABSTRACT

Background: Whole body scan using 131-iodine is performed to detect local recurrence or metastasis after thyroidectorny in differenciated thyroid cancer patients. The sensitivity of this procedure is related to the dose of radiopharmaceutical administered. It was reported that 131I posttreatment whole body scan demonstrate foci of tracer uptake not previously observed in diagnostic scan in 10~30% of cases. Posttreatment scans were most likely to reveal new foci in young patients(<45) and patients who had previously received radioactive iodine therapy. Method: We observed the frequency of discordant posttreatment scans and analysed the clicnical significance in 33 differenciated thyroid cancer patients who were admitted for radioiodine ablation from June, 1995 to April, 1996. Results: In 7 cases(21.2%), post treatment scan demonstrated cme or more foci of uptake and revealed less sites of uptake than diagnostic scan in 3 cases(9.1%). In one case with elevated thyroglobulin level and negative diagnostic scan, post treatment scan revealed new uptake sites with thyroid bed and cervical 1ymph node. The sites of discordant uptake were cervical lymph nodes in 4 cases and rnediastinal lymph node in one case, lung in one case, thyroid bed and cervical lymph nodes in one case, 3 cases of 7 pts(43%), demonstrated ane or more foci of uptake in post treatment scan, had history of previous radioiodine treatent. Conclusion: Post treatment scan confirmed uptake into remnant and metaststic tissues identified on the corresponding low dose diagnostic scans. Scanning after high dose radioiodine treatment frequently demonstrated one or more foci of uptake, especially in patients with previous radioiodine treatment, which were not visualized on the diagnostic low dose scan. Treatment scan may be useful for detection of remnant tissue or metastatic lesion in patients with elevated thyroglobulin and negative diagnostic scan.