Abstract
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Objectives The aim of the study is to assess wether 18F-Fluorodeoxyglucose PET CT (FDG PET) has any impact in the management of Iodine positive metastatic differentiated thyroid cancer (met. DTC).
Methods This is a retrospective review of patient records from 2006 to 2013 performed at a single institution, KFSH&RC, Riyadh, Saudi Arabia. A total of 68 patients with iodine positive met. DTC had recived FDG -PET scan are included in the study. There were 48 females and 20 males with mean age of 42.5 years (range 14 - 87 years ). FDG-PET was considered positive when at least one abnormal focus of FDG uptake was found and likewise for Iodine 123 whole body scan (I-123 WBS). The follow up period averaged 52 months ( range 6 - 78 months). I-123 WBS, thyrogloblin (Tg) and anti-Tg were reviewed for the assessment of treatment response. Results were reported as complete response (CR) when the I123 WBS was negative with negative Tg (Tg less than 2 with anti Tg less than 10), stable disease (SD) when there was no change and disease porogression (PD) when there were new metastic lesions with/without raised Tg.
Results Of the 68 patients, the distibution of metastatic lesions was nodal in 44, pulmonary in 33, and bone in 12 patients. Thirty patients (44%) were FDG-PET negative and 38 (56%) were FDG-PET positive. Out of the 30 FDG-PET negative patients, 27 (90%) had CR, 3 (10%) had SD and none had PD indicating good response to I-131 therapy. Out of the 38 FDG PET positive patients, 7 (18%) had CR and 31 (82%) had persistent disease as SD in 15 (40%) and PD in 16 (42%) indicating poor response to I-131 therapy.
Conclusions FDG PET is a powerfull tool to differentiate reponders from non responders to I131 therapy in patients with iodine positive met. DTC. FDG PET positive patinets showed poor response to I131 therapy. Whereas, patients who are FDG PET negative showed good response to therapy. These results show that when FDG PET is positive in patients with met. DTC, I131 therapy may not be effective and other modalties of therapy need to be considered.