A new type of whole-body magnetic resonance imaging (MRI) test could be an alternative to standard positron emission tomography/computed tomography (PET/CT) imaging for assessing cancer in children and young adults, but without exposure to radiation that has been shown to increase the risk of secondary cancers in later life.
In The Lancet Oncology, a research team from the Stanford University School of Medicine reports that the new scanning technique, which uses an iron supplement (ferumoxytol) to enhance tumour visibility, appears to be just as effective as PET/CT imaging with comparable sensitivities, specificities, and diagnostic accuracy.
"Although our initial results need to be confirmed in larger groups of patients, in our study whole-body MRI performed well enough to be immediately clinically applicable and could relieve young patients from the risks of radiation exposure due to medical imaging”, says Dr Heike Daldrup-Link, who led the research.
CT and 18F-fludeoxyglucose (18F-FDG) PET/CT scans are the main tests for assessing the extent of disease (staging) and to determine treatment planning and prognosis. Use of this technology has increased rapidly over the past several years and the potential cancer risks are well established, especially in children, who are more radiosensitive than adults and live long enough to encounter secondary cancers.
“Even with child-adapted low-dose protocols, patients undergoing a single 18F-FDG PET/CT scan are typically exposed to ionising radiation equivalent to roughly 700–750 chest radiographs (10–20 mSv) and four times the yearly background dose from natural radiation”, explains Daldrup-Link.
Ionising radiation in early childhood has been shown to roughly triple the risk of lifetime cancer compared with a person exposed over the age of 30 years, whilst cumulative exposure from diagnostic CT scans has been found to nearly triple the risk of developing secondary leukaemia and brain cancer in later in life.
In this study, the researchers compared the diagnostic accuracy of standard 18F-FDG PET/CT with an approach based on whole-body diffusion-weighted MRI combined with the iron supplement ferumoxytol, used “off label” as a contrast agent. Ferumoxytol is composed of ultra small superparamagnetic iron oxide particles which can be detected with MRI.
They scanned 22 children and young adults with malignant lymphomas and sarcomas using both whole-body MRI and 18F-FDG PET/CT and found much the same sensitivities (93.7% vs 90.8%), specificities (97.7% vs 99.5%), and diagnostic accuracy (97.2% vs 98.3%).