Simultaneously combining positron emission tomography (PET) and magnetic resonance (MR) has a higher capacity to map recurrent prostate cancer than the already high standard of integrated PET and computed tomography (CT), according to research presented at the 2013 Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging in Vancouver, British Columbia, Canada.

When prostate cancer makes a comeback, it becomes increasingly important to have exceptional imaging available to find all possible regions where cancer has spread to other parts of the body, or metastasized, in order to plan the best possible treatment. PET/MR provides superb soft tissue contrast with its MR component, compared to PET/CT, which focuses more on structure and density imaging with CT.

In this comparative study recurrent prostate cancer was imaged by both PET/MR and PET/CT with the molecular imaging agent C-11 choline. Choline is a naturally occurring B vitamin complex that is avidly bound by prostate cells upon injection, even those that have traveled through the bloodstream and taken up residence to develop metastatic tumors elsewhere. That is especially likely in the lymph nodes and bone.

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“The combination of PET, here with C-11 choline, and functional MRI provides complementary information that increases diagnostic certainty with higher detection rates, especially for more precise localization of recurrence. This could help to better tailor specific therapy, e.g., radiation of the pelvis versus antihormonal therapy, for patients with metastatic prostate cancer,” said lead scientist Matthias Eiber, MD, of the Technical University of Munich in Germany.

Methodology included a study population of 31 patients who had both PET/CT and PET/MR performed for restaging of recurrent prostate cancer with single injection of the imaging agent C-11 choline. PET/CT scans occurred about 5 minutes after injection, and PET/MR scans occurred about 51 minutes after injection.

Scans were interpreted separately, and all detected lesions were categorized according to suspected metastases as definitely, probably, or indeterminately metastatic. Researchers discovered that PET/MR found more areas of metastases (17 areas in 12 patients) compared with PET/CT (12 areas of metastases in eight patients). PET/MR also found more lymph node metastases, 42 versus 39 areas of interest with PET/CT. The same held true for bone metastases, 17 areas were detected in five patients with PET/MR and 14 areas were detected in four patients with PET/CT.

Simultaneous PET/MR is comparable to, if not more powerful than, PET/CT for recurrent prostate cancer. The only obvious challenge was a longer scan time than PET/CT, but it was found to be tolerable by patients undergoing PET/MR. Radiation exposure is considerably lower with PET/MR than with PET/CT. Many of these patients often undergo a series of examinations in the course of their disease; therefore, despite their high average age, radiation protection could be another argument for using PET/MR. This molecular imaging technique can now be considered a conceivable alternative to PET/CT for restaging prostate metastases, especially when small local tumor recurrences are involved.