Early PET/CT Scan Vital in Eroding Colorectal Live Metastases

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At theearly pet radiofrequency ablation (SNMMI) 2013 Annual Meeting, a study showed that early positron emission tomography (PET) and computed tomography (CT) imaging is efficient in detecting recurring areas of colorectal liver metastases following radiofrequency ablation.

Despite there being no official rules for the timing or interpretation of the images, the study determined it was best to use them 3 to 12 months following radiofrequency ablation.

Liver metastases are usually found in patients with colorectal cancer. In some instances, the abrasions can be successfully treated with radiofrequency ablation; and if recurring areas are detected early, radiofrequency ablation may also be used as treatment.

"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 a PhD student at the VU University Medical Centre in Amsterdam, the Netherlands, Karin Nielsen, MD.

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

The study aimed to put together specific guidelines for PET/CT interpretation following radiofrequency ablation and develop a timetable for follow-up analyses.

The study included patients who were treated with radiofrequency ablation for colorectal liver metastases and were then subjected to PET/CT scans in the 12 months following treatment. The researchers identified local-site recurrences as a rise in fluorodeoxyglucose uptake in the ablated area or its surroundings.

Nielsen and her peers examined 170 scans from 79 patients who had 179 ablated areas. From those patients, 72 percent were scanned in the 6 months following treatment. And of the 30 patients who developed a local-site recurrence, 90 percent come about in the 9 months following treatment and 96.7 percent transpired in the 12 months after treatment.

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

The study gathered useful results according to Darko Pucar, MD, from Georgia Regents University in Augusta, who was present at the SNMMI meeting, and could be very well put into medical/clinical practice.

"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. Sometimes, if something is very complicated, physicians don't act immediately. This is simple and actionable,” said Pucar.

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