Effect of external cooling on Lu-177 PSMA uptake for parotid glands.

Metastatic castration-resistant prostate cancer (mCRPC) patients have been started to treat with prostate-specific membrane antigen (PSMA) targeted radioligand therapy (PRLT), especially with Lu-177 PSMA-617 in recent years. But, side effects of PRLT against salivary glands, limits the treatment safety. Current study aims to show the effect of external cooling with icepacks on Lu-177 PSMA-617 uptake in parotid glands (PGs). Methods: Nineteen patients (Mean age 72.9 years) who had pre-treatment Gallium-68 (Ga-68) PSMA-11 Positron emission tomography/Computed tomography (PET/CT) with mCRPC referred for the first time for Lu-177 PSMA-617 treatment were included. Maximum and mean standard uptake values (SUVmax and SUVmean) of right (R) and left (L) PGs were measured on Ga-68 PSMA PET/CT before treatment without ice-pack applications. Before the initiation of PRLT, frozen icepacks were fixated unilaterally (all right sided) on PGs' of patients and applied approximately 5 hours. 4th and 24th h of PRLT, whole body planar scintigraphy images and 4th hour head/neck region single photon emission computed tomography/ computed tomography (SPECT/CT) scans were acquired after injection of Lu-177 PSMA-617. Region of interest (ROI) for R and L PGs and volume of interest (VOI) of SPECT counts, volume of CT of 4th hour R and L PGs were calculated. Results: Before the PRLT, Ga-68 PSMA-11 PET/CT scan without icepack application, showed no statistical significance between R and L PGs' SUVmax or SUVmean variables (p>.05). In the 4th and 24th hour of PRLT, on the planar images externally cooled R PGs' ROI's did not demonstrated any statistical difference when compared with L PGs which were not externally cooled(p>.05). SPECT/CT images in the 4th hour of PRLT had no statistical difference between R and L PGs' VOI counts. In addition, volumes of R and L PGs did not show any statistical difference between the glands (p>.05). Conclusion: External cooling of PGs in order to reduce Lu-177 PSMA-617 uptake with icepacks is not working at all.