Dr. Metser looking at scans
Dr. Ur Metser examining positron-emission tomography (PET) scan, computed tomography (CT) scan and the combined PET/CT images of a patient’s abdomen. (Photo: UHN StRIDe Team)

If every picture tells a story, then two pictures have the potential to tell a more complete story.

This appears to be true when two very different types of medical images – the computed tomography (CT) and positron-emission tomography (PET) scans – are superimposed to help diagnose cancer.

While a CT scan provides information about the location and structure of a tumour, a PET scan can visualize fast-growing cancerous cells. Combined, the two images can create a more accurate snapshot of the location and severity of a patient's cancer – characteristics that are used by physicians to determine the "stage" of a cancer.

Dr. Ur Metser, Head of Molecular Imaging in the Joint Department of Medical Imaging, which includes UHN, Mount Sinai Hospital and Women's College Hospital, recently led a study that provided the most conclusive evidence to date that PET and CT are a powerful combination for staging lymphoma – a common type of blood cancer. The study was performed in collaboration with Cancer Care Ontario and cancer centres throughout southern Ontario.

Dr. Metser's team compared the effect of using combined PET/CT to that of CT alone at diagnosis on the management and outcomes of 850 Ontarians with lymphoma.

Cover of Report 2019 

The researchers found that combined PET/CT enabled the detection of advanced disease in 18 per cent more patients than CT alone, and changed treatment plans for 40 per cent of patients. Importantly, PET/CT was linked to improved survival in patients with aggressive non-Hodgkin lymphoma.

"In this study, we show that combined PET/CT enables doctors to more accurately stage lymphomas at diagnosis and thus design effective treatment plans," says Dr. Metser, who is also affiliated with the Techna Institute and Princess Margaret Cancer Centre.

"Our findings also suggest that the use of combined PET/CT to inform disease management for certain lymphomas can lead to improved patient survival."

Improving clinical care through research

While the use of combined PET/CT for staging lymphomas was recommended by an international committee of experts in 2013, little prospective evidence existed to support the need for the extra PET scan at the time.

Dr. Metser's findings have since helped to bridge this gap in knowledge.

By revealing the positive impact of PET/CT on lymphoma care and patient outcomes, the findings have prompted Ontario's Ministry of Health and Long-Term Care to continue funding PET/CT scans for lymphoma care.

The findings have also ensured that Ontario clinical guidelines continue to recommend combined PET/CT for lymphoma.

As a result, the approximately 4,000 Ontarians that are diagnosed with lymphoma every year continue to benefit from receiving PET/CT scans as part of their care.

This study was supported by the Ministry of Health and Long-Term Care, Cancer Care Ontario and The Princess Margaret Cancer Foundation.

Double shot of scans and Dr. Metser
A combined PET/CT image, in which the CT scan reveals the location and distribution of a tumour and the PET scan highlights fast-growing cancer cells in red. (L). Dr. Metser with the combined PET/CT instrument used in the study. (Photos: UHN StRIDe Team)

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