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Integrated PET/CT in Differentiated Thyroid Cancer: Diagnostic Accuracy and Impact on Patient Management. J Nucl Med 2006; 47:616–624 報告者 : 蘇惠怡. Introduction.
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Integrated PET/CT in Differentiated Thyroid Cancer: Diagnostic Accuracy and Impact on Patient Management J Nucl Med 2006; 47:616–624 報告者:蘇惠怡
Introduction • Differentiated thyroid cancer (DTC): occurs in 3–5 per 100,000 people and represents about 1% of all malignant tumors • most cases : prognosis is favorable treatment consisting of primary surgery and ablative radioiodine administration achieves a 10-y survival rate of 80%–90% .
Introduction • special subgroups : less favorable with much lower survival rates. • Risk factors : (1) age > 45 y, (2) histopathologic grading, (3) poor radioiodine accumulation . Those patients without sufficient radioiodine uptake in the tumor cells have a significantly lower survival rate if distant metastases are present .
Introduction • Patients with DTC may have only iodine-negative tumor lesions or both iodine-negative and iodine-positive tumor tissue . →” the presence of iodine-negative tumor tissue decreases the accuracy of iodine scintigraphy “
Introduction • tumor tissue is not detected by iodine scintigraphy and will remain without further treatment • For the treatment of iodine-negative tumor tissue, surgery is the only curative therapy option. Exact localization of 18F-FDG tumor foci is mandatory for successful resection of cancer in these cases.
Materials and Methods • 40 patients : (1)elevated TG level in the euthyroid (2)the hypothyroid state or (3)morphologically suspected tumor disease (sonography, CT, MRI), • (1)L-thyroxin withdrawal for 4 wk before 131I whole-body scintigraphy, (2)low-iodine diet during this period, (3)thyroid-stimulating hormone increase of >30 mU/L
Materials and Methods • Exclusion criteria : (1)positive test for TG antibodies, (2)administration of CT contrast medium within the previous 6 mo, (3)positive iodine urine test performed on the day of scintigraphy, (4)pregnancy, (5)age <18 y.
Materials and Methods • (1)fasted at least 4 h before injection of 370 MBq 18F-FDG. (2)Blood glucose : <150 mg/dL (8.3 mmol/L). (3)Intravenous contrast agent: not administered. (4)the supine position with arms elevated, (5)CT scanning was started at the level of the cervicothoracic region • Scanning was started 60–90 min after the injection .
Materials and Methods • 5-point scale was used: 0 : the lesion was normal; 1 : the lesion was probably normal; 2 : the lesion was equivocal; 3 : the lesion was probably abnormal; 4 : the lesion was abnormal.
Materials and Methods • true-positive : score was 2–4 and histopathology was positive or if it showed progression at follow-up sessions. • true-negative :score was 0–1 and histology was negative or if follow-up examinations did not show any pathologic result in the region of concern for at least 18 mo. • false-positive : score was 2–4 and if histopathology was negative or if it showed no progression at follow-up sessions. • false-negative : score was 0–1 and if histology was positive or if follow-up examinations showed growth of the lesion(s).
Results (A) Preoperative PET showed intense 18F-FDG uptake in the suspected, left cervical lymph node as demonstrated on the coronal slice. (B) However, PET detected a second tumor focus that was located more caudally. For this second tumor, shown On the transverse PET slice. (C ) no corresponding abnormality could be localized on CT images . (D) Only by fusion of PET and CT images could the second lesion be precisely identified (located between esophagus and dorsolateral trachea) and be removed surgically.
Discussion • Three patients were identified on PET/CT as having a physiologic or nontumoral cervical 18F-FDG accumulation that was classified as lymph node metastases by PET alone and side-by-side PET and CT. • One limitation of 18F-FDG PET is especially in the region of the neck. →Specificity for detecting lymph node metastases could be increased by PET/CT
(A) pathologic 18F-FDG uptake in the right lower cervical region. (B) Corresponding CT slices did not reveal any abnormality. (C) PET/CT images clearly showed that the PET finding was located on the right vocal cord and corresponded to benign, muscular uptake. No surgery was scheduled and follow-up confirmed this benign finding.
Discussion • This was achieved in 3 patients by PET/CT detection of small and miliary lung metastases that were not diagnosed by PET alone. • This confirms the findings of previously reported studies showing that 18F-FDG PET is not able to adequately assess miliary lung metastases smaller than 6 mm. It is unclear whether this is generated from motion artifacts on inspiration and expiration or from a lower metabolic activity of the lung metastases .
Discussion • One important aspect of our study was evaluation of the therapeutic relevance of PET/CT.
Discussion • One limitation of our study seems to be that CT was performed without a contrast agent. → avoid blockage of iodine uptake. • Another limitation of the study is that the minimal time for follow-up of patients was 18 mo.
Conclusion • By precisely localizing tumor tissue, image fusion by integrated PET/CT is clearly superior to side-by-side interpretation of PET and CT images. • Integrated PET/CT is able to improve diagnostic accuracy in a therapeutically relevant way in patients with iodine-negative DTC.
