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Clinical Investigations |
1 Department of Nuclear Medicine, Chang Gung Memorial Hospital and Chang Gung University, Taoyuan, Taiwan
2 Department of Radiation Oncology, Chang Gung Memorial Hospital and Chang Gung University, Taoyuan, Taiwan
3 Department of Radiology, Chang Gung Memorial Hospital and Chang Gung University, Taoyuan, Taiwan
4 Institute of Nuclear Energy Research, Taoyuan, Taiwan
| ABSTRACT |
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Key Words: 18F-FDG PET nasopharyngeal carcinoma M0
| INTRODUCTION |
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Although the 5-y survival rate for overall NPC patients is high, around 90% of patients with distant metastases will die within 1 y (5,7). Thus, accurate staging and restaging of NPC are important for improving treatment and prognosis. In Taiwan, clinical staging comprises thorough physical examination and nasopharyngoscopy with biopsy sampling. CT or MRI of the head and neck is routinely done to assess the locoregional status, whereas chest radiography, liver sonography, and whole-body bone scanning are performed to exclude the possibility of distant metastasis. Previously, we have shown that MRI is superior to CT in determining the primary tumor extent, locoregional nodal metastases, and recurrent or residual tumors (1214). Tempering this advantage is the reality that MRI is currently impractical for a whole-body survey in a single examination. Furthermore, the inadequate sensitivity of chest radiography, liver sonography, and whole-body bone scanning in discerning small lesions may cause distant metastases to be underestimated and some metastatic lesions to be missed when treatment is planned.
Although previous reports indicated that 18F-FDG PET is superior to CT or MRI in detecting nodal status or local recurrence of NPC (15,16), the role of 18F-FDG PET in detecting distant metastatic NPC has not been addressed. We therefore conducted this prospective study to assess the efficacy of 18F-FDG PET in detecting distant metastases in NPC patients, with M0 staging based on conventional imaging.
| MATERIALS AND METHODS |
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PET Procedure
18F-FDG PET images were obtained with an ECAT EXACT HR+ camera (CTI) using a full width at half maximum of 4.5 mm and a transaxial field of view of 15 cm. All patients fasted for at least 6 h before PET. Serum glucose level was measured and diazepam (5 mg orally) routinely given before the intravenous administration of 370 MBq (10 mCi) of 18F-FDG. During imaging, patients kept their arms motionless over their head, aided by a headrest and a holding bar. Transmission scans were obtained with 68Ge rod sources. The emission and transmission scans were obtained in an alternating sequence per bed position. Reconstruction of both transmission and emission scans used accelerated maximum-likelihood reconstruction and ordered-subset expectation maximization (17,18), which reduces image noise and avoids artifacts resulting from filtered backprojection reconstruction of data with low count densities.
Image Analysis
Three experienced nuclear physicians who were unaware of other imaging results and the clinical data analyzed the 18F-FDG PET images using an interactive computer display. 18F-FDG accumulation was scored using a 5-point scale: 0 = normal, 1 = probably normal, 2 = equivocal, 3 = probably abnormal, and 4 = definitely abnormal (19). An 18F-FDG PET result of 3 or 4 was considered positive, and a grade of 0, 1, or 2 was considered negative. Interpretations were primarily based on visual analysis, using standardized uptake value as an accessory reference for abnormal 18F-FDG uptake. The latter evaluation was based on a region-of-interest analysis that yielded the standardized uptake value. The region of interest was placed within an area of pathologically increased 18F-FDG uptake on the attenuation-corrected image. The location of the edge of the region of interest was the contour for 75% of peak counts. Any difference of opinion was resolved by consensus.
Study Procedures and Determination of Lesion Status
All PET and conventional images were judged jointly by an NPC research team consisting of the nuclear medicine physicians, head-and-neck radiologist, otorhinolaryngologist, medical oncologist, and radiation oncologist. Confirmatory MRI or CT was performed to correlate the positive PET findings at the distant sites. CT-guided or sonography-guided biopsy was then performed to obtain a histopathologic diagnosis of distant lesions, if possible. If a biopsy of the lesion of interest was not feasible or yielded a negative result, follow-up MRI/CT or 18F-FDG PET was performed 36 mo later. Any discordance among the results of 18F-FDG PET, MRI/CT, and histopathologic studies were resolved by consensus.
Statistical Analyses
True and false imaging results were assessed on the basis of the histopathologic findings, when available, and on the posttreatment outcome. The
2 test, independent t test, and Fisher test were performed to compare the clinical characteristics and distant metastasis status for patient groups with primary and recurrent NPC. All statistical tests were 2-sided.
| RESULTS |
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3). Among them, true-positive lesions were found in 15 patients, false-positive lesions were found in 16, and both true-positive and false-positive lesions were found in the other 3. In total, 26 sites were true-positive and 21 were false-positive. Of the 18 patients with true-positive distant metastases, 14 had primary disease and 4 had relapsed disease. Fourteen of the 26 true-positive distant lesions (53.8%) were confirmed pathologically, whereas the other 12 (46.2%) showed definite progression in clinical or imaging follow-up. Of these 26 metastatic sites, 8 occurred in mediastinal lymph nodes, 5 in lung, 5 in liver, 5 in bone (Fig. 2), and 3 in other distant lymph nodes. All true-positive lesions in the lung were small (0.51.0 cm) and so were not resolved on chest radiography. Of the other 19 patients with false-positive sites, 8 had primary disease and the other 11 had tumor relapse. Of the 21 false-positive sites, 6 were in mediastinal lymph nodes (Fig. 3), 4 in lung, 1 in liver, 5 in bone, 2 in other distant lymph nodes, and 3 in other soft tissues. Granulation tissue or an inflammatory change was the most common cause (12/21, or 57.1%) of false-positive findings, followed by degenerative bone disease or posttraumatic changes (5/21, or 23.8%). During follow-up (from 5 to 14 mo after PET) of patients with distant metastases, 4 patients (11.8%) died with the disease present, 15 patients (44.1%) remained alive with disease, and the other 15 patients (44.1%) were still alive and disease free. When calculated on a patient basis, the sensitivity and specificity of 18F-FDG PET for distant metastases were 100% and 86.9%, respectively. With the help of 18F-FDG PET, 18 patients (12.9%) were discovered to have distant metastases, and their treatment was changed from curative locoregional to systemic.
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| DISCUSSION |
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Distant metastases of NPC, before and after primary definitive radiotherapy, are not uncommon (1,79). However, a detailed whole-body survey with MRI is generally impractical for tumor staging. Lack of a sensitive examination method may cause subtle and distant metastatic lesions to be missed at the time of diagnosis and result in undertreatment.
Recent retrospective analyses have supported the potential of 18F-FDG PET for the early identification of both tumor recurrence and lymph node metastases in NPC (15,16). As yet, the efficacy of 18F-FDG PET in the detection of unexpected distant metastases has not been studied. In the present study, 18F-FDG PET disclosed distant metastases in 13% of NPC patients with an initial stage of M0. Such an incidence of distant metastasis is higher than previously reported (1,5,6). Our results show that the sensitivity of 18F-FDG PET in detecting distant metastasis is higher than that of the conventional chest radiography, liver sonography, or bone scanning methods used to date.
The present study included patients with both primary and recurrent NPC. For those with primary NPC, N23 status was found to be an independent risk factor for distant metastasis (odds ratio, 3.27 95% CI, 1.4827.52) regardless of age, sex, cell type, and initial tumor stage. 18F-FDG PET scans revealed unexpected distant metastases in 11.9% (14/118) of patients with primary disease and 18.2% (4/22) of patients with tumor recurrence. Although the incidence of distant metastasis in the latter group was higher, the difference did not reach statistical significance (P = 0.486). Mediastinal lymph nodes were the most common sites for distant metastasis, followed by lung, liver, and bone. The distribution of distant metastases in our NPC patients differed from that found in previous studies, which showed that bone was the most common site, followed by the liver (5,21). Such a difference may stem from the fact that the previous studies assessed distant metastases by conventional imaging instead of 18F-FDG PET or CT, leading to underestimation of mediastinal lymph node or lung metastases. Although a previous study showed that conventional chest CT cannot provide adequate sensitivity to detect mediastinal lymph node metastases (1), modern CT techniques such as spiral CT or even multislice CT are better able to detect small lesions (22,23). Considering the rationale for the use of PET to detect distant metastases in NPC patients, our observation of the relatively higher overall detection rate for distant metastasis in recurrent than in primary NPC patients prompts us to suggest that PET should be performed on patients with recurrent NPC. The problematic (cost/benefit) but not less judicious indication is primary NPC, particularly if the incidences are not significantly different. Of note, in light of our data showing that a total of 80 NPC patients with N23 disease had a significantly higher risk of distant metastasis, primary NPC patients in such high-risk groups (nodal stage
2) will benefit substantially from early detection of distant metastases by the use of PET.
Of the 26 true-positive sites in this study, 14 were proven histologically and 12 were unequivocally established by lesion progression on follow-up imaging. Of the 21 false-positive sites in this study, 5 showed benign changes histologically, and all showed no progression during clinical or imaging follow-up of more than 6 mo. The presence of granulation or inflammation was the most common cause of false-positive findings (12/21, or 57.1%), followed by degenerative bone disease or posttraumatic changes (5/21, or 23.8%). Because of the still relatively high number of false-positive findings, every distant 18F-FDGavid area should be viewed with caution and considered for further cross-sectional imaging and, if feasible, histopathologic study for confirmation.
With the introduction of dual-modality PET/CT, the inherent limitation of 18F-FDG PETpoor anatomic resolutionhas been overcome. The sensitivity and specificity of this dual system are better than those of PET alone. The superiority of PET/CT to whole-body MRI in overall TNM staging (24) supports the usefulness of 18F-FDG PET/CT as a possible first-line modality for whole-body tumor staging. We did not use whole-body CT in staging NPC. Currently, chest radiography, liver sonography, and bone scanning are still the primary modalities for detecting distant NPC metastases in endemic areas, including France, Hong Kong, Taiwan, and Singapore. In a recent study from Singapore, chest radiography, bone scanning, and liver sonography were suggested only for node-positive patients (25). For node-negative and stage I patients, liver sonography was not suggested. However, with the increased availability of multidetector CT in such endemic areas, CT of the neck and chest should be included as part of the workup of NPC patients, especially those with N23 disease.
| CONCLUSION |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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For correspondence or reprints contact: Tzu-Chen Yen, MD, PhD, Department of Nuclear Medicine, Chang Gung Memorial Hospital, Linkou Medical Center, 5 Fu-Shin St., Kueishan, Taoyuan 333, Taiwan.
E-mail: yen1110{at}adm.cgmh.org.tw
| REFERENCES |
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