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E07 - Staging in the Molecular Era (ID 7)
- Event: WCLC 2013
- Type: Educational Session
- Track: Imaging, Staging & Screening
- Presentations: 1
E07.4 - PET/CT/MRI for diagnosis and staging of non-small cell lung cancer (ID 406)
14:00 - 15:30 | Author(s): Y. Ichikawa
Tumor diagnosis, tumor staging, and patient treatment in clinical oncology depend on morphological and molecular imaging procedures, such as magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET). Radiological and functional imaging studies, however, have well-known, inherent limitations that limit their diagnostic accuracy in assessing tumor stage and therapeutic response. Both CT and MRI provide mainly morphological information on the tumor and potential metastasis. However, the lack of functional information frequently limits the value of these studies when assessing lymph nodes metastasis. Accurate staging of patients with non-small cell lung cancer (NSCLC) is of paramount importance because stage significantly affects both treatment options and prognosis. The management of NSCLC often requires a multimodality approach for accurate diagnosis and staging and for patient treatment. Some of the most important advances in the treatment of lung cancer have been the development and implementation of accurate and functional imaging. In numerous studies the diagnostic capability of whole-body MRI, PET and PET/CT for cancer staging has been evaluated and compared. In the primary evaluation of pulmonary lesions, fluorodeoxyglucose (FDG)-PET scans are useful for distinguishing benign from malignant etiologies. Several studies investigating the accuracy of FDG-PET in diagnosing malignant pulmonary lesions have estimated its sensitivity and specificity to be 96.8% and 77.8%, respectively. In the same analysis, FDG-PET was found to be superior to CT for evaluating nodal and distant metastases and changed therapeutic management in 18% of the cases studied. However, PET has been shown to be less sensitive for characterizing smaller lung lesions. The positive predictive value (PPV) of FDG-PET is significantly lower for lesions smaller than 1 cm than for larger lesions (0.36 vs 0.90, p=0.015). The lower PPV for smaller lesions reflects a higher rate of false-positive FDG-PET scans. A comparison of the characteristics of PET-negative and PET-positive tumors has shown significant differences in lesion size (p < 0.001), histopathological type (p < 0.001), and pathological stage (p = 0.028). Both lesion size (p < 0.001) and histopathological tumor type (p < 0.001) were significant factors for determining whether PET results were negative or positive. This study established that negative PET findings were likely for lesions 2 cm or smaller and for adenocarcinomas (i.e., adenocarcinoma in situ and well-differentiated adenocarcinomas). A meta-analysis of 59 studies has shown that PET/CT is useful for detecting lymph node metastasis and extrathoracic metastasis. PET/CT is significantly more sensitive and specific than conventional CT alone and more sensitive than PET alone for staging NSCLC. Furthermore, PET/CT demonstrates excellent sensitivity (0.91) and specificity (0.98) for bone metastasis. However, PET/CT has high specificity but low sensitivity for detecting brain metastasis. The question of bone metastasis was most thoroughly answered by a recent meta-analysis of 17 studies comparing FDG-PET/CT, FDG-PET, MRI, and bone scintigraphy. The pooled sensitivity of each of the modalities in the detection of metastasis was 92%, 87%, 77%, and 86%, respectively, and the specificity was 98%, 94%, 92%, and 88%, respectively. When compared with other imaging modalities, FDG-PET appears to offer no additional information regarding the presence of metastatic disease in the brain. The current standard of care is to evaluate the brain metastasis with MRI in all patients, except those with clinical stage IA disease. A recent study of 1122 patients with PET-CT–determined stage I (T1-2N0) NSCLC suggests that invasive staging is not indicated for such patients, especially if a PET scan of the mediastinum is negative. Several studies have assessed the prognostic implications of mediastinal PET findings in patients undergoing curative resection of NSCLC. The rates of locoregional and distant recurrence are higher in patients with positive mediastinal PET findings than in patients with negative findings for the N0/N1 subset. The higher rate of locoregional failure in patients with positive preoperative PET findings in the mediastinum might lead to postoperative radiation therapy. Although chemotherapy is recommended for most patients with N1 disease, chemotherapy is generally not recommended for patients with N0 disease. The higher rate of distant failure in patients with positive preoperative mediastinal PET findings might lead to chemotherapy being recommended. On the other hand, pathologic confirmation with invasive mediastinal staging, either by mediastinoscopy alone or by mediastinoscopy combined with thoracotomy, is recommended if mediastinal lymph node abnormalities are detected with PET-CT. Several recent studies have shown that diffusion-weighted magnetic resonance imaging (DWI) has a higher specificity for N staging of NSCLC than does FDG PET/CT and has the potential to be a reliable alternative noninvasive imaging method for the preoperative staging of mediastinal and hilar lymph nodes in patients with NSCLC. Short inversion time inversion-recovery (STIR) turbo spin-echo (SE) MRI may be useful for distinguishing metastatic lymph nodes from nonmetastatic lymph nodes in patients with NSCLC. This imaging method might be more sensitive and accurate than CT, conventional T1-weighted MRI, FDG PET, or FDG PET/CT. We can prospectively compare the diagnostic capabilities of STIR turbo SE imaging, DWI, and FDG PET/CT for N staging in patients with NSCLC. In patients with NSCLC, quantitative and qualitative assessments of N staging obtained with STIR turbo SE MR imaging are more sensitive and more accurate than those obtained with DWI or FDG PET/CT. A new technology, PET-MRI, is now being established. To guarantee the clinically valuable, time- and cost-efficient use of PET/MRI, it is essential that appropriate indications be chosen, that cross-modality training be performed, that the acquisition protocols be optimized, and that the images be carefully reviewed, taking into account potential artifacts. Additional studies are needed to determine how PET/MRI might best be used clinically and to prospectively verify its clinical abilities. The increased use of FDG-PET will help clinicians to select the most appropriate treatments for each patient and thereby improve outcomes and avoid toxic therapies that are unlikely to be beneficial.
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