# Bladder activity of different PSMA PET radioligands and impact of furosemide

## TL;DR

This study compares how much radioactivity accumulates in the bladder during prostate cancer PET scans using different radioligands and shows that furosemide reduces this activity.

## Contribution

The study provides a direct comparison of bladder activity across multiple PSMA radioligands and demonstrates the effectiveness of furosemide in reducing it.

## Key findings

- 18F-PSMA-1007 had the lowest bladder activity, while 68Ga-PSMA-11 and 18F-DCFPyL had the highest.
- Furosemide significantly reduced bladder activity for 18F-rhPSMA-7.3 and 68Ga-PSMA-11.
- Bladder activity decreased with furosemide, and bladder volume increased significantly.

## Abstract

Prostate-specific membrane antigen (PSMA) radioligands used for PET imaging of prostate cancer (PCa) have variable urinary excretion. The prostate bed region is an important site of disease localization where intense bladder activity may obscure lesion detection. We performed a comparative analysis of the bladder activity of different PSMA radioligands and investigated the impact of furosemide administration on bladder activity reduction.

This is a retrospective analysis of PSMA PET/CT images of patients with PCa who were imaged with 68Ga-PSMA-11 with/without 20 mg furosemide, 18F-PSMA-1007, 18F-DCFPyL, 18F-rhPSMA-7.3 with/without 20 mg furosemide. Exclusion criteria were renal failure (eGFR < 60 mLs/min/m2), the use of a urethral catheter or nephrostomy tube in situ, or prior urinary diversion surgery. PSMA PET/CT images were acquired per published procedure standards. We determined and compared bladder volume and bladder activity level using mean and maximum standardized uptake values (SUVmean and SUVmax) between PET scans obtained with the different PSMA radioligands using an ANOVA or Kruskal-Wallis’s test, as appropriate. We also determined the association between the bladder activity level versus bladder volume using Spearman correlation.

210 PSMA PET/CT studies were reviewed, including 50, 20, 20, 28, 42, and 50 completed with 18F-PSMA-1007 without furosemide, 18F-rhPSMA-7.3 without furosemide, 18F-rhPSMA-7.3 with furosemide, 68Ga-PSMA-11 without furosemide, 68Ga-PSMA-11 with furosemide, and 18F-DCFPyL without furosemide, respectively. The median bladder SUVmean (range) without furosemide were: 1.75 (0.4–6.4) [18F-PSMA-1007], 10.00 (1.9–140.0) [18F-rhPSMA-7.3], 15.92 (2.0–106.0) [68Ga-PSMA-11], and 25.7 (7.9–87.6) [18F-DCFPyL], (P < 0.001). With 20 mg furosemide co-administered with the radiotracer, there was a significant decline in bladder activity level (median SUVmean of 10.00 (1.9–140.0) to 2.95 (0.8–17.6) for 18F-rhPSMA-7.3 and 15.92 (2.0–106.0) to 10.21 (2.6–281.3) for 68Ga-PSMA-11 and a significant increase in bladder volume, p < 0.05. There was a significant negative correlation between bladder SUVmax and bladder volume for the entire cohort, p = 0.008, r=−181.

There is variation in the bladder radioactivity between the different PSMA radioligands for PCa PET imaging, with 18F-PSMA-1007 demonstrating the lowest, 68Ga-PSMA-11 and 18F-DCFPyL the highest, and 18F-rhPSMA-7.3 intermediate bladder activity level. Administration of 20 mg furosemide produces a significant reduction in bladder activity and an increase in bladder volume. With 20 mg furosemide, bladder activity of 18F-rhPSMA-7.3 approaches that of 18F-PSMA-1007.