Therapeutic Response to Radiofrequency Ablation of Neoplastic Lesions: FDG PET/CT Findings

Abstract

Ablation of neoplastic lesions by using radiofrequency energy is gaining popularity in clinical practice because of the minimally invasive nature of radiofrequency ablation (RFA). Primary and secondary tumors of the liver and lung are treated with RFA when surgery is precluded because of comorbidity. Benign bone tumors are also treated with RFA to relieve pain and prevent further tumor growth. Differentiation between postablation tissue changes and residual disease is difficult with morphologic imaging modalities such as ultrasonography, computed tomography (CT), and magnetic resonance (MR) imaging, thus limiting the use of these modalities to detection of residual disease early after RFA. Fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) is a functional imaging modality that can be used to study the effects and efficacy of RFA. Lesions that show increased FDG uptake at PET become completely photopenic immediately after RFA, a finding that is suggestive of the completeness of ablation. Focal areas of increased FDG uptake within the ablated zone are suggestive of residual disease. Reactive tissue changes such as inflammation are depicted in the periphery of the ablated lesion and show a uniform low-grade FDG uptake, which can be differentiated from the focal, nodular intense uptake in areas of residual disease. Use of combined FDG PET/CT to detect residual disease early after RFA allows ablation to be repeated, if necessary, to obtain the maximum therapeutic benefit. Note that FDG uptake in the complications sometimes associated with RFA can be a cause of potential false-positive PET results.

Pulmonary radiofrequency ablation (Part 2): Procedure and follow-up

“…4,15,17---20,28 Many authors consider PET-CT to be more sensitive and specific for the assessment of response 4,23,26,27 and they recommend it for the follow-up, 4,5 but more research is necessary before we define its role. 28 CT is more accessible. 5 It should be performed with and without IV contrast before and after RFA 18 for the evolutionary measurement and comparison of contrast uptake.…”

“…18 The best time to perform the PET is not clear. 28 The inflammatory changes occurring the following weeks can increase the IV C uptake and the metabolic activity in PET-CT 23 (Fig. 1) which is a source of false positives.…”

“…1) which is a source of false positives. Although some authors defend performing a PET-CT in the first few hours (<48 h or ≤4 days) 19,28 to detect residual tumor before the inflammatory changes appear most of them recommend not performing it before one month 12 or even three months 4 since the metabolic hyperactivity of inflammatory causes does not stabilize until two months have gone by (Fig. 3).…”

Radiofrequency ablation: technique and clinical applications

“…For fluorodeoxy-Dglucose (FDG)-avid tumors, positronemission CT surveillance scans can also be performed. While elimination of a previously seen FDG-avid tumor with a thin and even activity around the ablation zone, which represents post-ablation inflammation, is an indicator of a complete ablation, presence of persistent asymmetric tracer uptake in the location of previously FDG-avid tumor suggests residual tumor (47).…”

Heme products post-radiofrequency ablation obscure tumor recurrence on MR but not on PET-CT

“…Focal areas of increased FDG uptake within the ablated zone are suspicious for residual or recurrent disease. Reactive tissue is typically present in the periphery of the ablated lesion and has uniform low-grade FDG uptake, unlike the focal nodular intense uptake observed with active tumor [6][7][8][9][10]. Fig.…”