San Francisco, CA USA (UroToday.com) Dr. Glenn Liu of University of Wisconsin Carbone Cancer Center discussed advances in NaF PET imaging and thoughts about incorporating it into routine clinical practice. He noted that understanding the most practical uses for advances in imaging techniques is particularly important for men after recent trial evidence suggested that the amount of metastatic disease may be associated with degree of response to various treatments. When comparing available techniques, traditional bone scans (99mTc-MDP scans) provide relatively simple two dimensional images that are widely available for a relatively low
cost and provide information regarding physiologic activity. In contrast, SPECT produces three dimensional images via a single photon emission CT scan, allowing physicians to identify smaller lesions by enhancing the ability to localize even small lesions anatomically. NaF PET/CT combines the pros of each of these methods by providing information about physiologic activity and superior anatomic localization. These scans are faster and more convenient than SPECT, and are more sensitive and specific than traditional bones scans and SPECT imaging (sensitivity and specificity reported to be 100% in J Nucl Med 2006; 47:287-97.). Diagnostic benefits include heightened accuracy during initial staging, an ability to detect metastatic disease or progressive disease earlier, and a more accurate quantitative measure of disease burden that may prove useful in prognosticating effects from certain therapies. However there is currently limited availability of NaF PET/CT, greater cost, and greater patient radiation exposure associated with NaF PET/CT imaging.
The incorporation of NaF PET/CT imaging into clinical practice may be challenging. Previous clinical trial data and extent of disease definitions were made using traditional imaging methods. When applying the CHAARTED definition of extensive disease to patients in clinical practice, it is likely that many more patients will meet the definition of extensive disease when using NaF PET/CT imaging that traditional scans. Whether patients who only meet criteria for extensive disease based on NaF PET/CT imaging will have the same outcomes as the men with extensive in CHAARTED is unknown.
Using NaF PET/CT may meet currently unmet needs in clinical trials and clinical practice. It is difficult to judge response or progression when using standard bone scan images for patients in both clinical practice and trial settings. The PCWG2 criteria attempt to resolve this for trial purposes by defining progression as “2+2”, or the development of 2 new lesions confirmed on subsequent imaging. Dr. Liu points out that this is inefficient, allowing our patients to continue on therapy that is not useful, and slows down drug development. NaF PET/CT may provide a more efficient method of monitoring progression by enabling us to perform quantitative bone imaging. Dr. Liu and colleagues are assessing the utility of doing this in a multi produces-institutional study evaluating repeatability and ease of response assessment during treatment of mCRPC. He has found that if a standard operating procedure is enacted, the results of NaF PET/CT scans are highly reproducible between readers. Additionally Dr. Liu presented a patient example of the team’s ability to identify changes in SUVmax and SUVtotal over time within each individual lesion. This allowed them to compare changes in physiologic activity during treatment and to describe each metastatic site as one that is responding or not responding to treatment. This technique can be particularly useful in heavily pre-treated mCRPC patients with heterogeneous metastatic sites in which therapies may have differential effects. In a second patient case example, Dr. Liu illustrated the utility of measuring both the SUVmax and SUVtotal in patients during treatment. In this case, treatment was able to decrease the SUVmax in a majority of metastatic sites, but measuring the SUVtotal over time revealed that the total disease burden was not decreasing. This corresponded with an initial PSA decline that relatively quickly began to increase indicating disease progression.
Ultimately, Dr. Liu described the benefit of using NaF PET/CT as a modality that could monitor physiologic activity with excellent anatomic localization both in routine clinical practice over time and as a method of more efficiently monitoring response in clinical trials. He reviewed the data indicating that NaF PET/CT is both highly sensitive and specific, and illustrated the benefit of using this quantitative modality. Finally, his recent study suggests that the results of NaF PET/CT scans are highly reproducible between readers, suggesting that this modality may soon be widely used in routine care.
Presented By:
Dr. Glenn Liu, MD
University of Wisconsin Carbone Cancer Center
Reported By:
Alicia K. Morgans, MD, at the 2016 Genitourinary Cancers Symposium - January 7 - 9, 2016 – San Francisco, CA
Assistant Professor of Medicine Medical Oncologist
Vanderbilt - Ingram Cancer Center