Ga-PSMA PET/CT: effect of external cooling on salivary gland uptake.

Objective: To evaluate the effect that external cooling of the salivary glands (ECSG) has on the uptake of gallium-68-labeled prostate-specific membrane antigen (Ga-PSMA), as an indirect assessment of the capacity of ECSG to reduce the local dose in lutetium-177-PSMA-617 radioligand therapy.

Materials And Methods: Ten patients with prostate cancer were submitted to Ga-PSMA positron emission tomography/computed tomography with unilateral ECSG. The ECSG was started at 30 min before the injection of the radiotracer and maintained until the end of image acquisition (1 h after injection). Each salivary gland was assessed by determining the maximum, mean, and peak standardized uptake values (SUVmax, SUVmean, and SUVpeak, respectively). The volume of each gland was determined in a volume of interest delineated by a threshold SUVmax of 10%. Paired Student's t-tests were used in order to compare the results.

Results: In terms of the SUV parameters, there were no statistically significant differences between the cooled and contralateral salivary glands. However, the mean volume was 27% lower in the cooled parotid glands than in the contralateral parotid glands ( = 0.004).

Conclusion: The use of ECSG does not appear to reduce Ga-PSMA uptake by the salivary glands. In addition, there is yet no evidence that ECSG is effective in preventing salivary gland toxicity.