18F]Fluorodeoxyglucose positron emission tomography surveillance of hepatic metastases from prostate cancer following radiofrequency ablation: a case report

The liver is the organ most commonly involved with metastatic disease. Surgical resection of hepatic metastases is the only potentially curative therapy, but it is possible in only 20 per cent of the patients. Radiofrequency ablation (RFA) of hepatic lesions is a therapeutic option for unresectable hepatic metastases. Today there is no clear consensus about which imaging technique is the most reliable to monitor RFA therapy. [18F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) is a new imaging modality allowing evaluation of glucose metabolism that has become established for monitoring therapy and early detection of recurrence of various types of malignant tumors. We present a case report of a 61-year-old man treated for prostate carcinoma 3 years earlier who presented with rising serum prostate-specific antigen (PSA) levels. A CT scan demonstrated two hepatic metastases that were treated with RFA because the patient refused surgery. During 3 years of follow-up hepatic recurrence was monitored with serum PSA levels, CT of the abdomen, and FDG-PET imaging on multiple occasions. On three separate occasions FDG-PET revealed hypermetabolic foci despite no definite evidence of recurrence on CT. Furthermore FDG-PET imaging 2 months after the last RFA therapy showed two large photopenic areas without evidence of hypermetabolism consistent with successful RFA therapy. Serum PSA levels correlated better with FDG-PET than CT results. We conclude that in this patient FDG-PET imaging was more accurate than CT for monitoring recurrence of hepatic metastases from prostate carcinoma after RFA therapy. PET demonstrated hypermetabolic foci when there was recurrence and no evidence of hypermetabolism early after successful RFA therapy. In addition FDG-PET imaging helped to guide the placement of the RFA probe to the most metabolically active part of the tumor.