PET/MR Outperforms PET/CT in Detecting Prostate Cancer Recurrence

The current so-called imaging gold standard for prostate cancer is the positron emission tomography combined with computed tomography (PET/CT). But the clinical need to identify small tumors is continuing to push imaging technology forward.

Siemens Biograph mMR

In a recent study, the new approach of combining PET with magnetic resonance (PET/MR) was shown to be more sensitive-compared with PET/CT-in detecting recurrent prostate cancer. The PET/MR approach detected more areas of recurrent metastatic disease, including more bone and lymph node metastasis compared with PET/CT.

“The main difference was the substantial higher detection rate of local recurrences in PET/MR compared to PET/CT,” said lead author Matthias Eiber, MD, of the Technical University Munich, Germany.

The results were presented at the Society of Nuclear Medicine and Molecular Imaging Annual Meeting held in Vancouver.

The PET/MR technique can now be considered a conceivable alternative to PET/CT for restaging prostate metastases, especially when small local tumor recurrences are involved, wrote the study authors (abstract 343).

The US Food and Drug Administration approved the first PET/MR device, the Biograph mMR system by Siemens Medical Solutions, in 2011. Another device, from Royal Philips Electronics, was approved later the same year. The technology can create both an MRI and a PET image without having the patient move between two different machines.

There are less than 20 whole-body PET/MR scanners installed in various institutions around the world. The Technical University Munich was the first institution worldwide where the scanner was installed at the end of 2010, according to Eiber.

A PET scan shows how tissues and organs in the body are functioning thanks to a radioactive tracer that is injected into the patient via the bloodstream. The MRI technology gives an image of soft tissues, bone, and organs in the body.

MR imaging is based on the amount of water in the body and results in finer detailed imaging compared with the x-ray–based CT scan.

PET/MR scanning takes longer than PET/CT but was found to be tolerable by patients. Another benefit of PET/MR is the lower radiation exposure compared with PET/CT, a likely important factor for patients who get sequential scans of their cancer over a relatively short period of time. The study found that PET/MR has the potential to reduce radiation exposure by as much as 80% compared with the PET/CT approach.

The current study directly compared images generated with PET/MR and PET/CT from 31 patients with recurrent prostate cancer. A molecular imaging molecule, ¹¹C-choline, was first injected into the bloodstream of patients, followed by PET/CT scans and PET/MR scans within 1 hour of the injection. Choline, a B vitamin complex, binds well to prostate cells, including metastatic prostate cancer cells outside of the prostate gland (such as in the bone or lymph nodes).

Each detected lesion was categorized as suspected, probable, or indeterminate metastasis. Researchers found they could detect more areas of metastasis (17 areas found in 12 of the patients) with PET/MR compared with PET/CT (12 areas detected in 8 of the patients).

According to Eiber, the PET/MR combination resulted in higher detection rates and more precise mapping of recurrent prostate tumors compared with the PET/CT approach. Metastatic bone areas were detected more frequently with PET/MR-17 areas in five of the patients, compared with 14 areas in four of the patients with PET/CT.

“Simultaneous PET/MR is comparable to-if not more powerful than-PET/CT for recurrent prostate cancer,” the study authors concluded.

The researchers are now investigating another prostate cancer–specific tracer, 68Ga-PSMA, which Eiber says could greatly improve prostate cancer imaging in the future.