PET/CT-led procedures show value in children

July 1, 2006

The literature is rife with studies touting the benefits of integrated PET/CT imaging versus PET or CT alone. But there is a surprising dearth of research examining the use of PET/CT-guided interventions, particularly in children. A study presented in May at the International Pediatric Radiology conference in Montreal is the first to show hybrid scanners are a welcome addition to interventional radiology suites in children's hospitals.

The literature is rife with studies touting the benefits of integrated PET/CT imaging versus PET or CT alone. But there is a surprising dearth of research examining the use of PET/CT-guided interventions, particularly in children. A study presented in May at the International Pediatric Radiology conference in Montreal is the first to show hybrid scanners are a welcome addition to interventional radiology suites in children's hospitals.

Dr. Kevin Baskin, a pediatric interventional radiologist at Children's Hospital of Philadelphia, and colleagues have conducted a retrospective theoretical study to predict the added benefit of PET/CT-guided biopsies over CT-guided biopsies alone. PET/CT fusion imaging could add significant benefits to children both in targeting metabolically active parts of tumors and in avoiding necrotic and hemorrhagic areas, they found. The research suggests that PET/CT can help practitioners choose safer routes to the target tissue and help avoid biopsies in cases where CT suggests abnormality but PET suggests benignity.

The researchers came to that conclusion by reviewing fused pediatric PET images performed at the Hospital of the University of Pennsylvania and CT images performed at CHOP. All of the children had open surgical biopsies, which, for the most part, could have been avoided using fusion imaging, Baskin said.

"We expect the data only to improve when the studies come from integrated scanners," he said.

Researchers at both institutions expect delivery of a PET/CT scanner within a year. Moving from theory to practice, they will initially target areas that are suspicious for recurrence of lymphoma. This is traditionally a tough call and can lead to repeated procedures to differentiate scar and recurrence. PET can answer the question and lead physicians to the tissue of interest. One case in the study involved a child who underwent two nondiagnostic mediastinoscopic biopsies performed on a mass within an 18-month period. A third biopsy, conducted by a surgeon guided by PET/CT fused data, demonstrated lymphoma.

"Had the PET/CT fusion information been available at the beginning, and had it been used to guide a percutaneous core biopsy-a minimally invasive alternative performed by an interventional radiologist-a diagnosis might have been achieved much sooner, and at much less cost, in this case, approximately $43,000 less," Baskin said.

Fusion imaging should be beneficial for the most common categories of pediatric tumors, such as lymphoma and sarcomas, and some other less usual pediatric tumors.

Imaging children carries particular challenges, including keeping them calm and still, which is especially crucial when dealing with FDG. The new PET/CT integrated scanners, with multislice technology and time-of-flight PET, can image the whole child in 10 minutes, Baskin said. Once the first PET/CT is acquired, all subsequent imaging can be performed by CT.

Another research team is using F-18 L-fluoro-dopa PET to help differentiate focal from diffuse congenital hyperinsulinism and then direct surgical interventions in the pancreas. The researchers, headed by Dr. Abass Alavi, chief of nuclear medicine at HUP, presented a study on the topic at the Society of Nuclear Medicine meeting in June.

"PET, and by extension PET/CT, simplifies the surgical management of children with hyperinsulinism. Instead of spending 10 hours in the operating room, surgeons spend less then two," he said.

The treatment for diffuse hyperinsulinism often entails surgery to remove 95% of the pancreas. Focal hyperinsulinism may potentially be cured if the focal area is surgically removed, because the remainder of the pancreas is normal. Traditional methods of identifying a tumor, such as CT, MRI, and ultrasound, have not been successful. In addition, children, often weighing as little as five pounds, may spend hours in the angiography suite. PET/CT makes angiography unnecessary and the reduction in radiation is significant, Alavi said.

There are a host of ultra short-acting radiopharmaceuticals that can be used therapeutically as well as diagnostically, Baskin said.

"Targeted delivery of radiopharmaceuticals and other agents can be accomplished using the same image fusion systems, whether they are PET/CT, PET/MR, or other combinations. Optical technologies are another avenue. All these open up a whole new spectrum of image-related interventions," he said.