Is there a role of 18F-FDG PET/CT in patients with malignant pleural mesothelioma after extrapleural pneumonectomy?

1032 Purpose: Malignant pleural mesothelioma (MPM) has a poor prognosis with low chance of cure despite the use of multimodality therapy including radical surgery. Although 18F-FDG PET/CT is known to be suitable imaging for evaluating tumor extent of MPM in patients considered for radical surgery, there are few studies on the role of PET/CT for diagnosis of recurrence after surgery. This study aims to find out whether post-therapeutic changes caused by radical surgery for MPM affect the diagnosis of local recurrence on 18F-FDG PET/CT. Methods: This retrospective study included patients who underwent extrapleural pneumonectomy (EPP) for MPM. Findings of postsurgical surveillance 18F-FDG PET/CT of the patients performed after EPP were analyzed. Maximum SUV of postsurgical bed activity (EPP-SUVmax), ratio to SUVmean of blood pool (EPP/BP ratio), and ratio to SUVmean of liver (EPP/L ratio) were measured. The maximum SUV of the postsurgical activity was measured at the site of the highest uptake on visual assessment. The time interval between surgery and PET/CT were divided 4 categories (P1: 1~6; P2: 7~12; P3: 13 ~24; P4: > 24 months) and the quantitative PET parameters were compared. Local recurrence was diagnosed by biopsy or by serial CT images or clinical follow up (FU). The PET parameters measured from sites of local recurrence (Lesion/BP ratio, Lesion/L ratio) were compared with those from surgical bed. Results: Twenty-eight 18F-FDG PET/CT of 17 patients were included between March 2009 and October 2020. Postsurgical activity measured from the surgical bed were not significantly different within 24 months after EPP, but was clearly low after 24 months (mean±SD EPP/BP ratio: P1, 3.4±2.13; P2, 3.2±1.60; P3, 3.9±1.47; P4, 2.1±0.57, p=0.225, and mean±SD EPP/L ratio: P1, 2.4±1.35; P2, 2.2±1.02; P3, 2.6±0.92; P4, 1.4±0.40, p=0.201). The 18F-FDG uptake measured from local recurrence in 11 cases was sufficiently higher than the postsurgical activity in 10/11 (91%) cases (mean±SD EPP/BP vs. Lesion/BP, 3.4±1.54 vs. 6.1±2.23, p < 0.001; mean±SD EPP/L vs. Lesion/L, 2.3±0.97 vs. 4.1±1.82, p < 0.001). In one case where the quantitative value of local recurrence was lower than that of postsurgical activity, recurrent tumor could be diagnosed because of the discrete pattern. The measurements from the recurrence lesion in this case was still higher than the immediately adjacent surgical bed. Half of the local recurrence occurred after 24 months. There were mediastinal, contralateral thorax, and extrathoracic recurrence in 9 18F-FDG PET/CT. Conclusions: Postsurgical 18F-FDG uptake of surgical bed after EPP in patients with MPM is lower than tumor uptake by local recurrence, especially 24 months after surgery. 18F-FDG PET/CT may be useful in detecting local recurrence after radical surgery such as EPP for MPM.