(UroToday.com) The 2023 GU ASCO annual meeting included a session on prostate cancer, featuring a presentation by Dr. Ashwin Parihar discussing the effect of body weight on standardized uptake values on 18F-DCFPyL PSMA PET/CT in patients with prostate cancer. Standardized uptake values on PSMA PET/CT are used as a semi-quantitative representation of in-vivo PSMA expression in prostate cancer. PSMA standardized uptake values have been used to determine eligibility for 177Lu-PSMA therapy in previous trials, and to predict response to therapy.
Additionally, higher lesion SUVmean has been shown to predict a favorable response to 177Lu-PSMA. It is known that 18F-FDG SUV is partly dependent on patient weight, and that the SUV corrected to lean-body mass is consistent across variations in body-weight. However, the variability of PSMA SUV with body-weight is unknown. Since SUVmean on PSMA PET/CT has important diagnostic, prognostic, and therapeutic implications, Dr. Parihar and colleagues sought to assess the variability of SUVmean on 18F-DCFPyL PET/CT with body-weight in men with prostate cancer.
The imaging database for this study was searched for men with prostate cancer who underwent 18F-DCFPyL PET/CT from 2021 to 2022. The authors grouped the patients by age and randomly selected a maximum of 20 patients from each of the six decades of age from 40s to 90s. 18F-DCFPyL PET/CT studies were reviewed on MIM v7.1.5 workstation and semi-automatic segmentations were performed to delineate and measure the SUV of the most tracer-avid lesion. Standardized uptake values from the liver and descending thoracic aorta (blood-pool) were also measured. Additionally, the SUV corrected to lean-body masses were derived using the Janmahasatian formula for body mass index. A partial correlation test was performed to assess the variability of SUVmean and SUV corrected to lean-body mass mean with body-weight.
A total of 85 18F-DCFPyL PET/CT studies in 85 men (mean age: 68.4 ± 11 years; mean weight: 94.5 ± 23.2 kg) were retrospectively analyzed. 18F-DCFPyL PET/CT was performed for evaluation of biochemical recurrence (n=56) or initial staging (n=29). At least one disease site compatible with prostate cancer was seen in 64 patients. Partial correlation tests were performed with 18F-DCFPyL dose, radiotracer uptake time and PSA value added as potential confounders for SUV. The blood-pool SUVmean (mean: 1.5 ± 0.6; r=0.48; p<0.0001):
and SUVmean of the most avid lesion (mean: 15.9 ± 17.4; r=0.33, p=0.01):
had a significant positive correlation with body weight. In contrast, liver SUVmean (mean: 5.4 ± 1.2) was not significantly correlated with body weight (p=0.5). The SUV corrected to lean-body mass mean of the most avid lesion (mean: 10.9 ± 10.9; p=0.06), and blood-pool SUV corrected to lean-body mass mean (mean: 1.0 ± 0.3; p=0.06) did not have a significant correlation with body weight. Patients with higher body weight can have falsely high SUVmean of prostate cancer lesions and of the background:
Dr. Parihar concluded his presentation discussing the effect of body weight on standardized uptake values on 18F-DCFPyL PSMA PET/CT in patients with prostate cancer with the following concluding messages:
- Body-weight corrected SUVmean has a significant correlation with patient weight and thus is not representative of the accurate PSMA expression
- As SUVmean is commonly utilized for patient selection in clinical trials and as a prognostic marker for 177Lu-PSMA therapy, these variations may lead to inaccurate outcome prediction
- SUV corrected to lean-body mass mean is a consistent representation of in-vivo PSMA expression and should be utilized for further studies of PSMA PET as a prognostic biomarker
Presented by: Ashwin S. Parihar, MBBS, MD, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO
Co-Authors: Lisa R Schmidt, John Crandall, Farrokh Dehdashti, Barry A. Siegel, Richard L. Wahl
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2023 Genitourinary (GU) American Society of Clinical Oncology (ASCO) Annual Meeting, San Francisco, Thurs, Feb 16 – Sat, Feb 18, 2023.