Abstract
Radiation-induced changes may cause a non-malignant high 2-deoxy-2-[18F]fluoro-d-glucose (FDG)-uptake. The 3′-deoxy-3′-[18F]fluorothymidine (FLT)-PET/CT performs better in the differential diagnosis of inflammatory changes and lung lesions with a higher specificity than FDG-PET/CT. We investigated the association between post-radiotherapy FDG-PET-parameters, FLT-PET-parameters, and outcome. Sixty-one patients suspected for having a relapse after definitive radiotherapy for lung cancer were included. All the patients had FDG-PET/CT and FLT-PET/CT. FDG-PET- and FLT-PET-parameters were collected from within the irradiated high-dose volume (HDV) and from recurrent pulmonary lesions. For associations between PET-parameters and relapse status, respectively, the overall survival was analyzed. Thirty patients had a relapse, of these, 16 patients had a relapse within the HDV. FDG-SUVmax and FLT-SUVmax were higher in relapsed HDVs compared with non-relapsed HDVs (median FDG-SUVmax: 12.8 vs. 4.2; p < 0.001; median FLT-SUVmax 3.9 vs. 2.2; p < 0.001). A relapse within HDV had higher FDG-SUVpeak (median FDG-SUVpeak: 7.1 vs. 3.5; p = 0.014) and was larger (median metabolic tumor volume (MTV50%): 2.5 vs. 0.7; 0.014) than the relapsed lesions outside of HDV. The proliferative tumor volume (PTV50%) was prognostic for the overall survival (hazard ratio: 1.07 pr cm3 [1.01–1.13]; p = 0.014) in the univariate analysis, but not in the multivariate analysis. FDG-SUVmax and FLT-SUVmax may be helpful tools for differentiating the relapse from radiation-induced changes, however, they should not be used definitively for relapse detection.
Highlights
Patients were eligible if they met the following inclusion criteria: Histologically confirmed lung cancer, i.e., non-small cell lung cancer (NSCLC) or small cell lung cancer (SCLC); definitive radiotherapy within 2 years and current suspicion of local relapse based on symptoms and/or CT- or FDG-PET/CT warranting FDG-PET/CT for relapse diagnosis
FDG- and FLT-uptakes in non-relapsed high-dose volume (HDV) were lower the longer after radiotherapy PET/CT was performed, whereas FDG- and FLT-uptakes were higher in HDVs with relapse the longer after radiotherapy
The FDG- and FLT-uptake was significantly higher in relapsed HDV than HDV
Summary
The early and precise diagnosis in patients suspected for lung cancer relapse is essential, as a curative intended treatment might be feasible [1]. The 2-deoxy-2-[18 F]fluoro-Dglucose (FDG)-PET/CT is recommended in patients with a clinical suspicion of recurrence of lung cancer after treatment [2,3]. A pathological confirmation is not always feasible. Concerns of risks associated with performing a biopsy and possibilities of sampling errors in small tumors rule out a biopsy in some patients.
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