Furosemide induced forced diuresis does not significantly impact ⁶⁸Ga PSMA-11 renal and urinary bladder activity and interpretative confidence.

Objectives: ⁶⁸Ga-PSMA-11 PET/CT is being increasingly utilized in patients with prostate cancer for initial staging, re-staging and recurrence evaluation. ⁶⁸Ga-PSMA-11 shows accumulation in the kidneys and the excretory activity is seen in the urinary bladder which can adversely affect diagnostic interpretation in the pelvic and retroperitoneal regions. Few studies have advocated the use of furosemide for reducing the radiotracer activity at these sites to improve diagnostic confidence. However, furosemide has its associated adverse effects, including urinary urgency and discomfort. We compared the radiotracer intensity in the kidneys and urinary bladder and the interpretative confidence for adjacent lesions in patients with prostate cancer who were administered ⁶⁸Ga-PSMA-11 with and without concurrent intravenous furosemide.

Methods: Medical records of 358 men with prostate cancer who underwent ⁶⁸Ga-PSMA-11 PET/CT between January 2018 and January 2019 at our institute were retrospectively reviewed. All patients were instructed to orally hydrate with 1 L of plain water at the time of radiotracer injection, and void frequently. Patients with urinary incontinence, non-compliance to oral hydration or any co-morbidities limiting fluid intake were excluded. We selected 30 patients that did not receive furosemide and 30 patients who had received 40 mg of intravenous furosemide at the time of radiotracer injection, using simple randomization,. Patient characteristics, indication for imaging, administered radiotracer activity and uptake time were recorded. The PET/CT images were reviewed by two nuclear medicine physicians who were blinded regarding the furosemide status. The mean and maximum SUVs were recorded for each kidney, parotid, aortic arch (blood-pool), liver and urinary bladder. Visual assessment of halo artefact around the kidneys and urinary bladder was done. The confidence of the readers in identifying the disease sites around the kidneys and urinary bladder was rated from 0-2 (0-insufficient image quality, 1-reduced quality, 2-sufficient image quality).

Results: There was no statistically significant difference in mean age, PSA levels, uptake time, SUV(max and mean) of the parotids, blood-pool and liver between the two groups. A halo artefact of mild intensity was seen in 2 patients with furosemide versus 1 without furosemide. No statistically significant differences in the SUVmax and SUVmean values for both the kidneys (SUVmean of the left kidney 21.1±9.8 vs 23.1±9.9; p=0.5) and urinary bladder (SUVmean 6±3.0 vs 7.3±4.5; p=0.2) were observed between the groups with and without furosemide, respectively. Urinary retention in 3 patients was observed only in the furosemide group where catheterization was required. The median diagnostic confidence in the identification of disease sites around the kidneys and urinary bladder was 2 in both groups.

Conclusions: Furosemide did not cause a significant change in the SUVmax or mean values at the kidneys and urinary bladder. Also, no change in the interpretative confidence was observed for the lesions in the pelvis and retroperitoneum, between the two groups. These findings are in contrast with the existing literature favoring the routine use of furosemide in reducing the radiotracer activity in the kidneys and urinary bladder. After validating these findings in a larger cohort, the use of furosemide could be avoided thereby reducing the potential for associated adverse effects.