Evaluation of qualitative and quantitative PET parameters in primary prostate cancer patients: double-match comparison of 18F-flotufolastat- and 68Ga-PSMA-11-PET

<title>Abstract</title> <p> <bold>Purpose</bold> To qualitatively and quantitatively compare ¹⁸ F-flotufolastat-PET and ⁶⁸ Ga-PSMA-11-PET urinary and lesion activity in a matched cohort of primary prostate cancer patients. <bold>Methods</bold> Data from patients who underwent ¹⁸ F-flotufolastat-PET or ⁶⁸ Ga-PSMA‑11-PET (n=62 each) were cohort-matched by disease characteristics. An experienced nuclear medicine physician assessed radiopharmaceutical activity retained in the bladder using a three-point qualitative scale (0 [none]/1 [moderate]/2 [severe]), and conducted a semi-quantitative analysis of retention in the bladder (0&lt;blood pool; 1≥blood pool and &lt;liver; 2≥liver and &lt;parotid; 3≥parotid). Primary tumours were evaluated visually by distance from bladder and impact of bladder activity. The presence of any ureter retention and halo artifacts were recorded. Quantitative assessments (SUV _mean/max ) were performed, and tumor-to-bladder ratios calculated and compared using Mann-Whitney-U-Tests. <bold>Results</bold> Overall interference from bladder activity was significantly greater with ⁶⁸ Ga-PSMA-11-PET than ¹⁸ F-flotufolastat-PET (scores=0, 1 and 2 were n=47, n=10 and n=5 for ⁶⁸ Ga-PSMA-11-PET, and n=60, n=2 and n=0 for ¹⁸ F-flotufolastat-PET; <italic>p</italic> =0.0006). Median bladder retention score was 2 for ⁶⁸ Ga-PSMA-11-PET and 0 for ¹⁸ F-flotufolastat-PET. 18% (3/17) and 0% (0/24) of primary tumors located near the bladder could not be differentiated from bladder retention in ⁶⁸ Ga-PSMA-11-PET and ¹⁸ F-flotufolastat-PET, respectively. Ureter retention was present in 21% (13/62) ⁶⁸ Ga-PSMA-11-PET and 0% (0/62) ¹⁸ F-flotufolastat-PET. Twenty-three ⁶⁸ Ga-PSMA-11-PET showed halo artifacts <italic>vs</italic> 4 ¹⁸ F-flotufolastat-PET scans. Median SUV _max in the bladder was 7.4 for ⁶⁸ Ga-PSMA-11-PET and 3.3 for ¹⁸ F-flotufolastat-PET ( <italic>p</italic> &lt;0.0001), and 14.7 and 19.7 in primary tumors, respectively ( <italic>p</italic> =0.1338). Resulting tumor-to-bladder ratios were significantly lower for ⁶⁸ Ga-PSMA-11-PET ( <italic>p</italic> &lt;0.0001). <bold>Conclusions</bold> ⁶⁸ Ga-PSMA-11-PET was significantly more impacted by bladder activity than ¹⁸ F-flotufolastat-PET. </p>