The role of PET scanning in radiofrequency ablation of liver metastasis from colorectal cancer

BACKGROUND Appropriate staging and follow-up evaluation of patients with liver metasta ses from colorectal cancer undergoing regional ablative treatment often req uire multiple imaging techniques and blood tests. We investigated the role of positron emission tomography (PET) in accurate staging and in monitoring the response to radio- frequency interstitial tissue ablation (RITA) of li ver metastases from colorectal cancer. METHODS Patients with unresectable metastases from colorectal cancer confined to th e liver and evaluated for the RITA procedure plus postablation chemotherapy were prospectively evaluated by the use of standard cross-sectional imagin g (computed tomography/magnetic resonance imaging), estimation of carcinoem bryonic antigen levels, and PET. The patients were followed up after surger y for 6 months by standard criteria of physical evaluation, laboratory test s, and imaging studies, including PET. RESULTS Our colorectal liver metastases PET database accrued 26 patients during the period of December 1998 to August 2000. In this group, a cohort of 18 pati ents evaluated for the clinical trial of RITA plus chemotherapy was analyze d for elucidation of the benefit of PET in accurate staging before treatmen t and in re response estimation 6 months following the RITA procedure. In 1 6.7% of patients (three of 18), PET demonstrated extrahepatic disease that had not been demonstrable by cross-sectional anatomic imaging studies. Of t he 15 patients undergoing RITA plus chemotherapy, 11 are evaluable after 6 months' follow-up. Correlation between computed tomography and PET demonstr ated that in 55% of patients (six of 11), PET is of discriminant value in d istinguishing the inactive, treated lesions from recurrent disease, whereas computed tomography is unable to do so. In the remaining 45% of patients, there was concordance between PET and computed tomography in estimating pro gressive disease. We propose a system of four groups (groups I to IV) based on PET's prognostic value. CONCLUSIONS PET enhances the staging accuracy In patients with unresectable colorectal metastases limited to the liver in whom regional ablative therapy is a cons ideration. PET is of value in the assessment of tumor response to radiofreq uency ablative therapy in most patients.