Using 18FDG-PET and Other PET Agents in Oncology Clinical Trials
This is an excerpt from our free eBook, “Using 18FDG-PET and Other PET Agents in Oncology Clinical Trials.” To access the full eBook, click here.
THE USE OF PET IN ONCOLOGY CLINICAL TRIALS
18F FDG PET Imaging in Solid Tumors and Response Assessments
18F FDGPET is not only an important tool to use for staging and response evaluation in lymphoma trials, but it can play an important role in the evaluation of solid tumors. For example, many tumors (lung, head and neck, breast, colon, pancreas, melanoma, and others) are FDG-avid and are now routinely included as part of standard-of-care imaging for diagnosis and staging. That means that during a clinical trial, many investigators will have their patients undergo both CT (or MRI) and PET scans as part of their RECIST 1.1. assessments. Although not considered an acceptable substitute for anatomic imaging, RECIST 1.1 guidelines do provide recommendations on using 18FDG-PET in solid tumor trials, utilizing qualitative (but not quantitative) assessments for response evaluation while continuing to base the overall responses on size-criteria as the method for primary assessment.
The most utilized criteria for the evaluation of 18F FDG-PET in solid tumor clinical trials are the EORTC6 and the PERCIST criteria7, which took many of the features of EORTC and further defined specific conditions for determining a metabolic response. Using a fixed small region of interest of about 1 cm3 in volume (1.2-cm diameter) in the most active region of metabolically active tumors to minimize statistical variability, the assessment of SUV measurements in the 1 (up to 5 optional) most metabolically active tumor focus as a continuous variable is performed at screening and subsequent time points. A complete metabolic response (CMR) requires complete normalization of FDG activity in all tumor lesions, while a partial metabolic response (PMR) requires a 30% decline in SUVs with an absolute change in SUV by 0.8 units from baseline. Progressive metabolic disease (PMD) relies on a 30% increase in 18F-FDG SUVs, with >0.8 SUV unit increase in tumor SUV from the baseline scan in a pattern typical of tumor and not of infection/treatment effect. Stable metabolic disease is neither CMR, PMR or PMD. Finally, the SUV uptake in normal liver tissue (or mediastinal blood pool, if the liver is abnormal) between scans has been incorporated in the response assessment readouts as a marker of the reliability of the SUV estimates. This is performed by placing a 3.0 cm3 ROI on normal reference tissue to ensure that the SUV measurements are within 0.3 SUV units between time points. If not, reliance on SUVs as an indicator of response or progression should proceed cautiously.
6 Young H, Baum R, Cremerius U, et al: Measurement of clinical and subclinical tumour response using [18F]-fluorodeoxyglucose and positron emission tomography: Review and 1999 EORTC recommendations—European Organization for Research and Treatment of Cancer (EORTC) PET Study Group. Eur J Cancer 35:1773-1782, 1999.
7 From RECIST to PERCIST: Evolving Considerations for PET response criteria in solid tumors. Wahl RL, Jacene H, Kasamon Y, Lodge MA. J Nucl Med. 2009 May;50 Suppl 1:122S-50S.
