Comparison of 18F-FDG PET and Bone Scintigraphy in Detection of Bone Metastases of Thyroid Cancer Shinji Ito1,2, Katsuhiko Kato1, Mitsuru Ikeda3, Shingo Iwano1, Naoki Makino2, Masanori Tadokoro4, Shinji Abe5, Satoshi Nakano5, Masanari Nishino5, Takeo Ishigaki1, and Shinji Naganawa1 1Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Japan; 2Department of Radiology, Toyota Memorial Hospital, Toyota, Japan; 3Department of Radiological Technology, Nagoya University School of Health Sciences, Nagoya, Japan; 4Department of Radiology, Fujita Health University School of Health Science, Toyoake, Japan; and 5Department of Radiology, Nagoya University Hospital, Nagoya, Japan Key Words: bone metastases; differentiated thyroid carcinoma; We compared the efficacies of 18F-FDG PET and 99mTc-bone 99mTc-bone scintigraphy; 18F-FDG PET scintigraphy for the detection of bone metastases in patients J Nucl Med 2007; 48:889–895 with differentiated thyroid carcinoma (DTC). Methods: We DOI: 10.2967/jnumed.106.039479 examined 47 patients (32 women, 15 men; mean age 6 SD, 57.0 6 10.7 y) with DTC who had undergone total thyroidectomy and were hospitalized to be given 131I therapy. All patients underwent both whole-body 18F-FDG PET and 99mTc-bone scin- tigraphy. The skeletal system was classified into 11 anatomic Skeletal imaging by 18F-FDG PET has been shown to segments and assessed for the presence of bone metastases. be useful in the detection of bone metastases of breast (1–6), Bone metastases were verified either when positive findings lung (1,4,7,8), thyroid (4), esophageal (4,9), gastric (4), 201 were obtained on .2 imaging modalities— Tl scintigraphy, colorectal (4), endemic nasopharyngeal (10), renal cell 131 I scintigraphy, and CT—or when MRI findings were positive (11), prostate (1), ovarian (4), and testicular (4) carcinomas. if vertebral MRI was performed. Results: Bone metastases 18 were confirmed in 59 of 517 (11%) segments in 18 (38%) of the In most of these studies, F-FDG PET was proven to be 99m 47 study patients. The sensitivities (visualization rate) for bone superior to conventional scintigraphic imaging using Tc- metastases on a segment basis using 18F-FDG PET and 99mTc- labeled phosphate compounds (99mTc-methylene diphospho- bone scintigraphy were 50 of 59 (84.7%) and 46 of 59 (78.0%), nate [99mTc-MDP] or 99mTc-hydroxymethylene diphospho- respectively; the difference between these values was not nate [99mTc-HMDP]). For the detection and evaluation of statistically significant. There were only 2 (0.4%) false-positive bone metastases of various kinds of carcinomas, 99mTc-bone cases in a total of 451 bone segments without bone metastases when examined by 18F-FDG PET, whereas 39 (8.6%) were false- scintigraphy has been used widely because of its overall high positive when examined by 99mTc-bone scintigraphy. Therefore, sensitivity and the easy evaluation of the entire skeleton (12). the specificities of 18F-FDG PET and 99mTc-bone scintigraphy However, 99mTc-bone scintigraphy leads often to false- were 449 of 451 (99.6%) and 412 of 451 (91.4%), respectively; positive lesions and, consequently, its specificity is reduced, the difference between these values was statistically significant because degenerative or inflammatory foci will be often 18 99m (P , 0.001). The overall accuracies of F-FDG PET and Tc- confused with metastatic diseases. bone scintigraphy were 499 of 510 (97.8%) and 458 of 510 Differentiated thyroid carcinoma ([DTC] papillary and (89.8%), respectively; the difference between these was also statistically significant (P , 0.001). Conclusion: The specificity follicular) is characterized by good prognosis in comparison and the overall accuracy of 18F-FDG PET for the diagnosis of with carcinomas of other organs. The 10-y survival rate of bone metastases in patients with DTC are higher than those of DTC is .80% because of treatments such as total thyroid- 99mTc-bone scintigraphy, whereas the difference in the sensitiv- ectomy and ablation of remnants with radioiodine (13). ities of both modalities is not statistically significant. In compar- However, metastases of thyroid carcinoma develop in 7%– 99m 18 ison with Tc-bone scintigraphy, F-FDG PET is superior 23% of patients; the distant metastases occur commonly in because of its lower incidence of false-positive results in the de- tection of bone metastases of DTC. the lungs, bones, and brain, and bones are the second com- mon site of metastases from thyroid carcinoma (14). Several earlier reports showed that 18F-FDG PET is Received Jan. 8, 2007; revision accepted Mar. 16, 2007. highly sensitive in detecting DTC and is particularly useful For correspondence or reprints contact: Katsuhiko Kato, MD, PhD, Department of Radiology, Nagoya University Graduate School of Medicine, for the evaluation of patients with negative radioactive 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan. 15 E-mail: [email protected] iodine scintigraphy and elevated thyroglobulin levels ( – COPYRIGHT ª 2007 by the Society of Nuclear Medicine, Inc. 20). For the detection of bone metastases of thyroid BONE METASTASES OF THYROID CANCER • Ito et al. 889 TABLE 1 TABLE 3 Incidence of Bone Metastases in 11 Bone Segments of Sensitivity, Specificity, and Overall Accuracy of 18F-FDG Patients with DTC PET and 99mTc-Bone Scintigraphy in Detection of Bone Metastases in Patients with DTC Bone segments with Bone segment metastases (no.) 99mTc-Bone Parameter 18F-FDG PET scintigraphy P Cervical spine 3 Thoracic spine 9 Sensitivity (%) 50/59 (84.7) 46/59 (78.0) 0.45* Lumbar spine 11 Specificity (%) 449/451 (99.6) 412/451 (91.4) ,0.001 Sacrum with coccyx 7 Accuracy (%) 449/510 (97.8) 458/510 (89.8) ,0.001 R pelvis 8 L pelvis 8 R scapla and clavicle 4 *Not significant. L scapla and clavicle 1 Sternum 0 R ribs 3 L ribs 5 FDG PET and 99mTc-bone scintigraphy was, at most, 1 mo. At the Total 59 start of the study, 25 (53%) of the 47 study patients had metastases to the cervical lymph nodes and 20 (43%) had distant metastases in the lungs and mediastinal or supraclavicular lymph nodes. 99m carcinoma, Tc-bone scintigraphy has been also used Histopathologic Type widely. However, to our knowledge, there have been no Fifteen (32%) and 29 (62%) of the 47 study patients had systematic comparative studies on the efficacies of 18F- follicular and papillary carcinomas, respectively. In the other 3 FDG PET and 99mTc-bone scintigraphy in the detection of (6.4%) patients, the pathologic type was unknown, but they were bone metastases of thyroid carcinoma. The purpose of this diagnosed as having DTC by clinical and radiologic follow-up. study was to compare 18F-FDG PET and 99mTc-bone scin- Bone Scintigraphy tigraphy in the detection of bone metastases of DTC. 99mTc-Bone scintigraphy was performed 3 h after intravenous injection of 555 MBq 99mTc-HMDP (Nihon Medi-Physics, Ltd.) MATERIALS AND METHODS or 740 MBq 99mTc-MDP (Daiichi Radioisotope Laboratories, Subjects Ltd.). Anterior and posterior whole-body planar images were ob- All procedures followed the clinical guidelines of Nagoya tained with high-resolution collimation on a dual-head g-camera University Hospital and were approved by the International Review (E.CAM; Toshiba Corp.). At least 2 experienced radiologists in- Board. Written consent was obtained after a complete description terpreted the planar images visually. of the study was given to all patients and their relatives. Forty-seven PET Procedure patients (32 women, 15 men; mean age 6 SD, 57.0 6 10.7 y), who The patients fasted for at least 6 h before PET. Scanning had DTC and had undergone total thyroidectomy, were selected for was performed using 18F-FDG and a Headtome-V PET scanner 131 study. All patients were hospitalized to be given I therapy for (Shimadzu). 18F-FDG (296 MBq) was injected intravenously 40 18 ablation of remnants and underwent both whole-body F-FDG min before imaging. Whole-body emission/transmission images 99m 18 PET and Tc-bone scintigraphy to detect bone metastases. F- were obtained simultaneously. At least 2 experienced radiologists 99m FDG PET and Tc-bone scintigraphy were performed from 3 to interpreted the coronal and axial images visually. 30 d before the radioiodine therapy, and the interval between 18F- Data Analysis TABLE 2 The presence of bone metastases was assessed in 11 bone Difference in Patient Populations between Bone Metastases- segments: cervical, thoracic, and lumbar spines, sacrum with Positive and -Negative Groups of Patients with DTC coccyx, right and left pelves, sternum, right and left scapulae with clavicles, and right and left ribs. At least 2 experienced Bone metastases radiologists diagnosed bone metastases using 201Tl scintigraphy, 131 Parameter Positive Negative Total I scintigraphy, CT, plain film radiography, or MR images. The presence of bone metastases was verified by the following defi- Male* (no.) 4 (27) 11 (73) 15 (100) nitions. First, the positive findings for bone metastases must be Female* (no.) 14 (44) 18 (56) 32 (100) obtained in .2 imaging modalities—201Tl scintigraphy, 131I y Average age (y) 58.0 6 12.4 56.4 6 9.7 57.0 6 10.7 scintigraphy, and CT. Second, if vertebral MRI was performed, Follicular 13 (87) 2 (13) 15 (100) the MRI findings must indicate the positive metastases. It has been carcinoma* (no.) Papillary 3 (10) 26 (90) 29 (100) demonstrated that MRI shows high sensitivity and specificity in carcinoma* (no.) detecting bone metastases (21–23). When the positive finding for Unclear (no.) 2 1 3 bone metastases was detected in only 1 modality other than MRI, the bone segment showing such a finding was excluded, because it was unclear whether such a lesion was bone metastasis. Among *Values in parentheses are percentages. the total 517 bone segments examined, 7 segments (1.4%) were ex- yMean 6 SD.