Biodistribution of the ¹⁸F-FPPRGD₂ PET radiopharmaceutical in cancer patients: an atlas of SUV measurements

Purpose: The aim of this study was to investigate the biodistribution of 2-fluoropropionyl-labeled PEGylated dimeric arginine-glycine-aspartic acid (RGD) peptide (PEG3-E[c{RGDyk}]2) (¹⁸F-FPPRGD₂) in cancer patients and to compare its uptake in malignant lesions with ¹⁸F-FDG uptake. Methods: A total of 35 patients (11 men, 24 women, mean age 52.1 ± 10.8 years) were enrolled prospectively and had ¹⁸F-FPPRGD₂ PET/CT prior to treatment. Maximum standardized uptake values (SUV_max) and mean SUV (SUV_mean) were measured in 23 normal tissues in each patient, as well as in known or suspected cancer lesions. Differences between ¹⁸F-FPPRGD₂ uptake and ¹⁸F-FDG uptake were also evaluated in 28 of the 35 patients. Results: Areas of high ¹⁸F-FPPRGD₂ accumulation (SUV_max range 8.9 – 94.4, SUV_mean range 7.1 – 64.4) included the bladder and kidneys. Moderate uptake (SUV_max range 2.1 – 6.3, SUV_mean range 1.1 – 4.5) was found in the choroid plexus, salivary glands, thyroid, liver, spleen, pancreas, small bowel and skeleton. Compared with ¹⁸F-FDG, ¹⁸F-FPPRGD₂ showed higher tumor-to-background ratio in brain lesions (13.4 ± 8.5 vs. 1.1 ± 0.5, P < 0.001), but no significant difference in body lesions (3.2 ± 1.9 vs. 4.4 ± 4.2, P = 0.10). There was no significant correlation between the uptake values (SUV_max and SUV_mean) for ¹⁸F FPPRGD₂ and those for ¹⁸F-FDG. Conclusion: The biodistribution of ¹⁸F-FPPRGD₂ in cancer patients is similar to that of other RGD dimer peptides and it is suitable for clinical use. The lack of significant correlation between ¹⁸F-FPPRGD₂ and ¹⁸F-FDG uptake confirms that the information provided by each PET tracer is different.