Objective: The objective of this study was to evaluate the 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) findings following complete radiofrequency ablation (RFA) treatment of malignant lung tumors.
Methods: Follow-up PET and computed tomography examinations in 18 patients (mean age, 67 ± 16 years [range, 30–91 years]; 10 males, 8 females) who underwent 19 RFA sessions for the treatment of primary (n = 14) and metastatic (n = 5) lung tumors with mean follow-up of 18 months (range, 12–24 months) were retrospectively reviewed by 2 thoracic radiologists. All tumors were completely ablated. The maximum standardized uptake value (SUV) of the tumor and surrounding lung at baseline and at 1, 6, 12 and 24 months after RFA was measured. In addition, the size, histology, location of the tumor, presence of underlying emphysema, electrode type, and complications from RFA were recorded. Data were analyzed using Fisher exact test.
Results: Baseline tumor SUV was variable (mean, 1.8 ± 1.5 [range, 0.7–7]). The post-RFA 18F-FDG-PET appearances could be divided into 2 groups. A ring of peripheral activity and central photopenia was seen following 13 (68%) of 19 of ablations, and no ring was noted following 6 (32%) of 19 of ablations. The ring of 18F-FDG-PET activity was present at 1 month in 62%, at 6 months in 69% and at both 1 and 6 months in 31%. In all cases, central photopenia at 1 or 6 months was replaced by increased activity as the ring resolved at 6 or 12 months, mimicking local tumor progression. The presence of a ring of activity was associated with the use of a cluster electrode (P = 0.01). Lesion size, histology, location, baseline SUV, electrode type, or development of cavitation following RFA were not significantly associated with a post-RFA ring (P > 0.05) on PET scans. At 12 or 24 months, the SUV in the center of the lesion was equal to or greater than the SUV at baseline in 9 (47%) of 19 cases.
Conclusions: Recognition of the normal FDG-PET appearances after RFA is important to prevent misdiagnosis of local tumor progression.