Impact of external cooling with icepacks on 68Ga-PSMA uptake in salivary glands

Background: External cooling of the salivary glands is advised to prevent xerostomia in lutetium-177-PSMA treatment for advanced prostate cancer. Since evidence addressing this subject is sparse, this study aims to determine impact of icepacks application on uptake in salivary glands. Eighty-nine patients referred for gallium-68-PSMA PET/CT for (re)staging of prostate cancer were prospectively included. Twenty-four patients were scanned with unilateral (solely left-sided) icepacks; 20 with bilateral icepacks; 45 without icepacks. Icepacks were applied approximately 30 minutes prior to tracer injection. PET/CT acquisition started 1 hour postinjection. Radiotracer uptake was measured in the parotid- and submandibular glands. Results: When comparing the intervention group with the control group, uptake in the left parotid gland significantly differed: SUVmax: 11.07 +/- 3.53 versus 12.95 +/- 4.16; p = 0.02. SUVpeak: 9.91 +/- 3.14 versus 11.45 +/- 3.61; p = 0.04. SUVmax and SUVpeak were reduced with 14.52% and 13.45%. All other SUV values did not significantly differ. Patients with bilateral icepacks showed no significant differences in PSMA uptake compared to the control group (all: p > 0.05). Intra-patient analysis revealed some significant differences in SUVmax and SUVpeak between the cooled and non-cooled parotid gland (SUVmax: 11.12 +/- 3.71 versus 12.69 +/- 3.75; p = 0.00. SUVpeak: 9.93 +/- 3.32 versus 11.25 +/- 3.25; p = 0.00). Conclusions: Impact of icepacks on PSMA uptake seems to be limited to the parotid glands. As clinical relevance of these findings is debatable, structural application of icepacks in the setting of lutetium-177 PSMA therapy needs careful consideration.