Liver and mediastinum SUV in F-18 FDG PET/CT: Impact of immunotherapy

598 Objectives The SUV of the liver or mediastinum is often used as an internal reference (IR) to which lesion SUV can be compared. Therefore, it is essential that the IR SUV remain consistent, particularly for cancer patients in whom pre and post therapy PET/CT studies are used in assessing response to therapy. We aimed to determine whether or not immunotherapy affects liver &/or mediastinum SUV max measurements in melanoma patients. Methods Sixteen melanoma patients (6 M, 10 F; mean age 51 yrs) who underwent serial whole -body FDG PET/CT scans (n=48) were retrospectively evaluated. For the 48 scans, SUVmax scores over the disease free mediastinum & liver regions were obtained from initial baseline & 2 sequential post immunotherapy follow up exams. Volumeteric SUVmax was obtained from a 500mm2 ROI in the liver (rectangular ROI within the mid-right lobe) and similarly in the mediastinum (elliptical ROI within the aortic arch). SUVmax scores in each region were grouped into: A (from initial scan), B (first post immunotherapy scan) & C (second post immunotherapy scan). Descriptive statistics & ANOVA test to assess the differences in SUVmax between the 3 groups in each region were done. Results The mean differences of SUV max between the 3 groups in each region were statistically & clinically not significant, mediastinum (P=0.937) & liver (P= 0.851). Conclusions We conclude that, in melanoma patients, liver and/or mediastinum are quite stable IR that can easily be used in insuring the technical quality of the PET protocol as well as the reproducibility of SUV measurement. In so doing, assessing response to cancer therapy can be attained in a more accurate way