Quantitative and Qualitative Assessment of Urinary Activity of 18F-Flotufolastat-PET/CT in Patients with Prostate Cancer: a Post Hoc Analysis of the LIGHTHOUSE and SPOTLIGHT Studies
Phillip H. Kuo, Rick Hermsen, R. H. C. Penny, Ernst J. Postema
Abstract
Abstract Purpose To evaluate the impact of urinary activity on interpretation of 18 F-flotufolastat ( 18 F-rhPSMA-7.3) PET/CT, we conducted a post hoc qualitative and quantitative analysis of scans acquired in two phase 3 studies of 18 F-flotufolastat. Procedures Newly diagnosed or recurrent prostate cancer patients enrolled in LIGHTHOUSE (NCT04186819) or SPOTLIGHT (NCT04186845), respectively, underwent PET/CT 50–70 min after intravenous administration of 296 MBq 18 F-flotufolastat. For the present analysis, 718 18 F-flotufolastat scans (352 from LIGHTHOUSE and 366 from SPOTLIGHT) were re-evaluated by three board-certified nuclear medicine physicians. Reader 1 performed a quantitative assessment ( SUV max and SUV mean ) of bladder activity in a circular region-of-interest over the maximum diameter of bladder activity in the transverse plane. All three readers qualitatively assessed the impact of any urinary activity in the bladder on image interpretation using a three-point scale (0 = no/minimal visible urinary activity, 1 = urinary activity visible but distinction between urine and disease possible and 2 = assessment inhibited by urinary activity) and the presence/absence of ureteric activity and halo artifacts. Results In total, 712/718 scans were evaluable. Reasons for exclusion were cystectomy, renal failure, or urinary catheter in situ ( n = 2 each). The median bladder SUV max and SUV mean were 17.1 and 12.5, respectively. By majority read, 682/712 (96%) patients had either no urinary activity (score = 0) or visible activity that could be distinguished from disease uptake (score = 1). In the minority of patients (24, 3.4%) where urinary activity did impact assessment (score = 2), the median bladder SUV mean was higher (20.5) than those scored 0 (3.8) or 1 (14.0). Ureteric activity was absent in 401 (56%) patients. Halo artifacts were observed in only two (0.3%) patients (majority read). Conclusions 18 F-Flotufolastat urinary activity did not influence disease assessment for the majority of patients. While this study was not designed as a head-to-head comparison, the median bladder SUVs are lower than previously reported values for other renally cleared PSMA-PET radiopharmaceuticals.