PET/CT 3 MONTHS AFTER LIVER METASTATECTOMY 

VANCOUVER, British Columbia — Early positron emission tomography and computed tomography (PET/CT) imaging is effective at identifying local-site recurrences of colorectal liver metastases after radiofrequency ablation. Although there are no guidelines for the timing or interpretation of images, they are best used 3 to 12 months after radiofrequency ablation, according to a new study.

Liver metastases are common in patients with colorectal cancer. In some cases, the lesions can be effectively treated with radiofrequency ablation. If local-site recurrences are caught early enough, they can also be treated with radiofrequency ablation.

"Most physicians use contrast-enhanced CT or MRI to do follow-up on these patients, although there is literature that suggests a beneficial role for PET/CT because of the added metabolism factor that you have with PET," said Karin Nielsen, MD, a PhD student at the VU University Medical Centre in Amsterdam, the Netherlands.

Dr. Nielsen presented the research here at the Society of Nuclear Medicine and Molecular Imaging 2013 Annual Meeting.

"We know that the sensitivity and specificity between normal CT and PET/CT differs by 10% to 15%," so you miss a significant number of local-site recurrences, Dr. Nielsen told Medscape Medical News. When you see them in follow-up scans, they could be too large for repeated treatment, she noted.

The researchers set out to develop criteria for PET/CT image interpretation after radiofrequency ablation and to determine a timetable for follow-up analyses.

The study involved patients who underwent radiofrequency ablation for colorectal liver metastases and then underwent PET/CT in the 12 months after treatment. They defined local-site recurrences as increased fluorodeoxyglucose uptake in the ablated region or adjacent to it.

Dr. Nielsen and colleagues analyzed 170 scans from 79 patients with 179 ablated regions. Of those patients, 72.2% were scanned in the 6 months after treatment. Of the 30 patients who developed a local-site recurrence, 90.0% occurred in the 9 months after treatment and 96.7% occurred in the 12 months after treatment.

"The problem of incomplete ablation is notorious; that's why follow-up is so important after that treatment," said Dr. Nielsen. "PET is absolutely important in the first year after ablation, but not before 3 months," she added. Just 2% of lesions smaller than 1 cm and 4% of lesions smaller than 2 cm showed a local-site recurrence.

These findings should be clinically useful, according to Darko Pucar, MD, from Georgia Regents University in Augusta, who attended the session.

"In clinical practice, you need to apply very firm criteria, but something that is easy to apply, not only for academic doctors, but also for practitioners. What I like about this study is that they provide relatively clear guidelines," Dr. Pucar told Medscape Medical News. "Sometimes, if something is very complicated, physicians don't act immediately. This is simple and actionable."

Dr. Nielsen and Dr. Pucar have disclosed no relevant financial relationships.

Society of Nuclear Medicine and Molecular Imaging (SNMMI) 2013 Annual Meeting: Abstract 67. Presented June 9, 2013.