Dr. Zinn added that interpretation of MR images in PET/MR scanning will be more difficult than CT was for PET/CT scanning. “Some feel nuclear medicine physicians will be replaced by radiologists in the future,” he said in an e-mail. “Nuclear medicine was able to add CT training, but that will be harder to do for MR.”
Explore This IssueApril 2011
Finding enough board-certified radiologists to read PET/MR scans may be one early challenge, he said.
New PET Tracers
PET scanning has been limited by the availability of the tracers used to detect tumors. The most commonly used tracer, fluorodeoxyglucose, or FDG, highlights areas of glycolysis, which is heightened in tumor cells. FDG can lead to false positives, however, because glycolysis is also heightened during inflammation and tissue repair.
New tracers are being developed to tailor to other metabolic activities that could give insights into what is happening in cancer cells, Dr. Wax said, citing a study from the Journal of Nuclear Medicine (2010;51:66-76).
“Every cancer is not the same, and with improved probes to image specific processes, we can tailor our therapies and treatments to the individual patient,” Dr. Zinn said. “Right now we can treat tumors differently depending on certain classification. But we can probably do a lot better at characterizing them by using molecular markers to help us know exactly how to treat, and, more importantly, during the treatment, to evaluate whether the tumor’s changing.”
Immuno-PET tracers, in which specially formulated antibodies are particularly reactive with a receptor that is more highly expressed in tumor cells, is an area of great promise, Dr. Wax said.
Epidermal growth factor-based and vascular endothelial growth factor-based antibodies are among those being used in these tracers.
18-F-FLT (18-F fluorodeoxythymidine) and 18-F-FMISO (18-F fluromisonidazole) are two of the more promising agents. FLT would help assess tumor proliferation, and FMISO is used to gauge hypoxia.
“It’s possible that we may be able to target specific areas of tumor sites, where they’re undergoing metabolic changes, parts of the tumor that are hypoxic, parts of the tumor that are showing angiogenesis, and then be able to target our therapies towards those areas,” Dr. Wax said. That’s really abstract, pie-in-the-sky type things, but I think that’s along the lines of what we’re trying to do.”
Dr. Wax emphasized that the new tracers are still only the subject of lab work, and the cost is an unknown. Any training would involve the interpretation and preparation of the materials, but how long that training would take is also undetermined, he said.