Post-therapeutic dosimetry of 177Lu-DKFZ-PSMA-617 in treatment of patients with castration resistant prostate cancer

Objectives The objective of this study was to evaluate the radiation dosimetry of 177Lu- prostate specific membrane antigen (177Lu-DKFZ-PSMA-617) in castration resistant prostate cancer (CRPC) patients.

Methods After obtaining ethical clearance from the institute ethics review board, we enrolled CRPC patients who were positive on Glu-NH-CO-NH-Lys-(Ahx)-[68Ga(HBED-CC)] PET/CT scan. For kidney protection a cocktail of lysine and arginine diluted in 2 litres of normal saline was infused, starting from 30-60 minutes before 177Lu-DKFZ-PSMA-617 infusion. The mean administered activity in the overall population was 2.52 ± 1.3GBq. For dosimetry purpose, each patient underwent 9 planar whole body scans along with blood and urine sample collection upto 168 hours. SPECT/CT was done to derive the volume of parotid glands, submandibular glands and tumour. Dosimetric evaluation was done using the OLINDA/EXM 1.0 software.

Results 26 CRPC patients with a mean age of 66.30 ± 9.95 years (range: 38-81) were recruited. Normal physiological uptake was seen in all the patients in lacrimal glands, parotid glands, submandibular glands, liver, spleen, kidneys, intestines and urinary bladder. Organs having highest absorbed doses were the salivary glands (parotid and submandibular) followed by the kidneys, receiving 1.24 ± 0.268 mGy/MBq and 0.99 ±0.31 mGy/MBq, respectively. The mean absorbed doses to the liver, urinary bladder and red marrow were 0.36 ± 0.108 mGy/MBq, 0.243 ± 0.09 mGy/MBq and 0.048 mGy/MBq, respectively. The mean total body dose was 0.016 mGy/MBq and the mean effective dose equivalent was 0.106 mGy/MBq. Interestingly, we observed that Delker et al (2015), and Kabasakal et al (2015) who did not infuse amino acid for renal protection had reported similar absorbed dose to kidneys, thus utility of amino acid infusion is question marked.

Conclusions 177Lu-DKFZ-PSMA-617 therapy is a safe option in the treatment of CRPC patients. There is no additional benefit, from the renoprotective point of view, from amino acid infusion in 177Lu-DKFZ-PSMA-617 therapy.