The role of FDG-PET/CT in detecting unsuspected and unknown distant metastasis in the initial staging of NSCLC

Turkish Journal of Medical Sciences Turk J Med Sci (2014) 44: 1029-1040 © TÜBİTAK doi:10.3906/sag-1311-104 http://journals.tubitak.gov.tr/medical/ Research Article The role of FDG-PET/CT in detecting unsuspected and unknown distant metastasis in the initial staging of NSCLC 1, 1 1 1 1 Metin HALAÇ *, Meftune ÖZHAN , Sabire YILMAZ AKSOY , Betül VATANKULU , Anar ALIYEV , 1 2 1 1 Sertaç ASA , Ersan ATAHAN , Muhammet Sait SAĞER , Kerim SÖNMEZOĞLU 1 Department of Nuclear Medicine, Cerrahpaşa Faculty of Medicine, İstanbul University, İstanbul, Turkey 2 Department of Chest Diseases, Cerrahpaşa Faculty of Medicine, İstanbul University, İstanbul, Turkey Received: 26.11.2013 Accepted: 23.01.2014 Published Online: 24.10.2014 Printed: 21.11.2014 Background/aim: Our purpose in this retrospective study was to determine the ratio of unexpected [metastases within the coverage area of thorax computed tomography (CT)] and unknown (metastases out of the coverage area of thorax CT) metastases by positron emission tomography/CT (PET/CT) in patients with newly diagnosed non-small cell lung cancer (NSCLC) who had no defined metastatic lesion, and to investigate the contribution of fludeoxyglucose (FDG)-PET/CT in metastasis staging. Materials and methods: A total of 567 patients (489 males and 78 females, mean age 60.9 ± 10.7 years) were enrolled in this study. Among the 567 patients, a total of 156 patients who underwent PET/CT for metabolic characterization (group 1) and had solitary pulmonary nodules (group 1a, n = 39) or solitary pulmonary masses (group 1b, n = 117) and the remaining 411 patients (group 2) with NSCLC who had PET/CT performed for staging formed the basis of this study. Results: In group 1, 5/39 (12.8%) patients with a solitary pulmonary nodule and 29/117 (24.8%) patients with a solitary pulmonary mass had distant metastases. In group 2, 129 patients of 411 (31.4%) had distant metastasis. Conclusion: FDG-PET/CT is proven to be an effective method in detection of unsuspected-unknown metastasis, either in patients with solitary pulmonary lesion or in the initial staging of patients with NSCLC. Key words: 18F-FDG, NSCLC, unsuspected and unknown metastases 1. Introduction Lung cancers are one of the most common causes of death related to cancer (approximately 18%) and approximately 3,000,000 people get cancer every year (1). Non-small cell lung cancers (NSCLCs) constitute 75%–80% of all lung cancers (2). The high recurrence rate (greater than 20%) after curative resection is probably due to undetermined occult-small metastatic lesions that are present at the first diagnosis (3). Treatment is determined predominantly by the stage of NSCLC at initial diagnosis. The accuracy of the diagnostic workup is crucial for adequate therapeutic planning. Patients with limited disease (stages I, II, and IIIA) are candidates for curative surgery. In contrast, patients with advanced disease (stages IIIB or IV) are considered to be incurable (4). In the latter group, unnecessary surgical procedures performed with a curative intent can be avoided by accurate staging, and palliative treatment options should be considered for these patients. Patients * Correspondence: considered for surgery undergo imaging tests such as radioisotope bone scan, computed tomography (CT) of the chest and abdomen, and CT or magnetic resonance imaging (MRI) of the brain to detect metastases in order to avoid unnecessary surgery. Recently, numerous studies have indicated that the addition of positron emission tomography (PET) or PET/CT using the glucose analog 18F-fludeoxyglucose (FDG) exhibits higher diagnostic accuracy than CT alone and is also cost-effective when implemented into the staging of NSCLC (5–9). Because PET or PET/CT is a whole-body imaging modality, it is also an efficient imaging method for assessment of thoracic and extrathoracic metastases of NSCLCs in a single session. For the patients with NSCLC, the determination rate of unknown metastases via FDGPET or PET/CT has been found as 6%–20% (7,10–12). High sensitivity of the PET/CT in showing unexpected distant metastases may reduce unnecessary noncurative surgical procedures for NSCLC. Our purpose in this 1029 HALAÇ et al. / Turk J Med Sci retrospective study is to determine the ratio of unexpected (within the coverage area of thorax CT) and unknown (outside of the coverage area of thorax CT) metastases by PET/CT in patients with newly diagnosed NSCLC who had no defined metastatic lesion in conventional thorax CT and thus to investigate the contribution of FDG-PET/ CT in metastasis staging. FDG-PET is also a highly sensitive method for assessing solitary pulmonary nodules. In a metaanalysis (n = 1474) performed by Gould et al. it was found that, in solitary lung lesions of greater than 1 cm, the sensitivity of FDGPET was extremely high (96.8%) and the specificity was relatively low (77.8%) (13). Our other purpose in this study is to investigate the ratio of the unknown or unexpected metastases in patients with solitary pulmonary lesions (nodule or mass) who underwent PET/CT for metabolic characterization. 2. Materials and methods 2.1. PET/CT imaging and assessment protocol PET/CT studies were performed by using a 6-slice multidetector CT integrated high-resolution PET scanner (Siemens Biograph LSO HI-REZ PET/CT, USA) on patients with a minimum 4-h fasting blood glucose level of ≤150 mg/dL and 1–1.5 h after an intravenous FDG injection.. First a topogram and then a low-dose nonenhanced CT of the region consisting of the vertexproximal femur were taken, and finally PET images of the same region were taken. In the assessment of PET/CT imaging attenuation-corrected PET images were analyzed as a standard. Nonattenuation-corrected images were also analyzed when needed. A higher FDG uptake than physiological background activity was accepted as PET positivity. Maximum standard uptake value (SUVmax) was calculated from the most active region among the PET-positive lesions. 2.2. Patient group A total of 567 patients (489 males and 78 females, mean age 60.9 ± 10.7 years) were enrolled in this retrospective study. Among the 567 patients, a total of 156 patients who underwent FDG-PET/CT for metabolic characterization (group 1) and had solitary pulmonary nodules (spn, group 1a, n = 39) or solitary pulmonary masses (spm, group 1b, n = 117) on thorax CT and the remaining 411 patients (group 2) with a diagnosis of NSCLC who underwent FDG-PET/CT for staging formed the basis of this study. 2.2.1. Group 1: Metabolic characterization group The patients with a solitary lesion of ≥1 cm in the lung parenchyma, as determined by thorax CT, were evaluated by FDG-PET/CT for metabolic characterization. A total of 156 patients (35 females, 121 males, mean age 62.6 ± 1030 10.8) who had increased FDG uptake in the lung lesion (SUVmax of ≥2.5) were included in this group. Of the 156 patients, 39 had a solitary pulmonary nodule with increased FDG accumulation (spn, (...truncated)