RADIATION FREE IMAGING TECHNIQUE

A radiation-free alternative for staging malignant tumors in children and adolescents combines 2 MRI techniques and enhances images with the iron supplement ferumoxytol, according to a new study.

The results were published online February 19 in the Lancet Oncology.

Although the initial results need to be confirmed in larger groups of patients, the approach "performed well enough to be immediately clinically applicable and could relieve young patients from the risks of radiation exposure due to medical imaging," said senior author Heike Daldrup-Link, MD, from Stanford University in California, in a press statement.

"We carefully designed our study so that it could be widely applied," she told Medscape Medical News. "Any larger children's hospital with an MRI scanner capable of obtaining whole-body images can offer this test right now.... However, there are a variety of hurdles that will likely make clinical translation a more lengthy process," she acknowledged.

The researchers "are to be commended for their efforts in realizing this innovative concept," writes Thomas Kwee, MD, from Medical Centre Utrecht in the Netherlands, in an accompanying comment.

He agrees that the approach is technically feasible and has potential diagnostic value, but notes that "several important issues still need to be addressed" before the new technique becomes a clinical alternative to the current standard.

The current standard is PET/CT with the radiotracer ¹⁸F-fluorodeoxyglucose (FDG), which is associated with substantial exposure to ionizing radiation and an increased risk for secondary cancers.

Whole-body MRI has the advantage of being radiation-free. However, until now, the utility of whole-body MRI for tumor staging has been hampered by various limitations, such as short-term gadolinium enhancement and poor delineation of tumors in the spleen and bone marrow, note the researchers.

Ferumoxytol, which is approved by the US Food and Drug Administration (FDA) for the treatment of anemia, can be used as an off-label contrast agent to overcome some of these issues because it contains iron oxide nanoparticles with superparamagnetic properties, they explain.

"The unique properties of iron oxide particles have overcome some of the major limitations of whole-body diffusion-weighted MRI that have prevented its use for tumor staging in clinical practice," Dr. Daldrup-Link explained. "These include long-lasting enhancement (ferumoxytol can enhance vessels for more than 24 hours) and the ability to visualize tumors in the spleen and bone marrow that may have previously have gone unnoticed."

With ferumoxytol enhancement and the combination of whole-body diffusion-weighted MRI (for tumor detection) and whole-body T1-weighted MRI (for anatomic orientation), the researchers report obtaining "diagnostic images very similar to an ¹⁸F-FDG PET/CT scan," with "equivalent sensitivities, specificities, and staging results."

"To our knowledge, this is the first study in pediatric patients and adolescents that integrates an MRI technique for tumor detection (whole-body diffusion) with an MRI technique for anatomical orientation (ferumoxytol-enhanced, T1-weighted images), in accordance with the concept of integrated ¹⁸F-FDG PET/ CT scans," Dr. Daldrup-Link and colleagues write.

Comparison of the 2 Techniques

The study involved 22 children and young adults with malignant lymphomas and sarcomas who were scanned with both the experimental whole-body ferumoxytol-enhanced MRI and standard ¹⁸F-FDG PET/CT.

The results showed good agreement for tumor staging between the experimental and standard methods in sensitivity (93.7% vs 90.8%), specificity (97.7% vs 99.5%), and diagnostic accuracy (97.2% vs 98.3%).

Mean exposure to ionizing radiation was lower with the experimental than with the standard method (12.5 vs 0.0 mSv), and there were no adverse reactions associated with ferumoxytol.

"Our findings suggest that ferumoxytol-enhanced whole-body diffusion-weighted MRI could provide an alternative to ¹⁸F-FDG PET/CT, free of ionizing radiation, for staging of children and young adults with cancer," the researchers conclude.

Dr. Daldrup-Link has received inquiries from around the country about ferumoxytol imaging, she toldMedscape Medical News, but there remain obstacles to using it in clinical practice.

"Right now, ferumoxytol is FDA-approved as an intravenously administered iron supplement for the treatment of anemia in adult patients. To use this as a contrast agent in children, we need, at a minimum, approval from the local ethics committee and, better (as we did), Investigational New Drug approval from the FDA," said Dr. Daldrup-Link, who is cochair of the American College of Radiology Pediatric Imaging Research Committee.