99mTc-HYNIC-PSMA-11 Whole-Body SPECT/CT: A Clinically Viable Alternative to 68Ga-PSMA PET/CT in patients with Prostate Cancer

Objectives The diagnostic performance of 99mTc-HYNIC-PSMA-11 whole body SPECT/CT versus 68Ga-PSMA PET/CT was evaluated in prostate cancer patients. Methods As a part of the diagnostic workup, all the prostate cancer (PCa) patients (n = 10; mean age 66.4 ± 9.6 years) underwent whole-body 68Ga-PSMA-11 PET/CT followed by serial whole body (anterior and posterior) 99mTc-HYNIC-PSMA-11 imaging The serial whole body imaging was performed at multiple time points of 10 min, 2 h, 4 h, 6 h, 24 h and the whole body SPECT/CT was acquired at 3 h. The whole-body SPECT/CT data was analyzed for lesions detection and to calculate the standardized uptake values (SUVmax) for 99mTc-HYNIC-PSMA-11 avid lesions using the Q- Metrix software. These values were compared with the corresponding SUVmax values obtained from 68Ga-PSMA-11 PET/CT. The serial whole body imaging data were used for estimating the radiation absorbed doses (mSv/MBq) to various organs using the MIRD schema and the OLINDA/EXM software. Results 68Ga-PSMA-11 PET/CT identified a total of 64 metastatic lesions, while 99mTc- HYNIC-PSMA-11 SPECT/CT detected 49/64 metastatic lesions, presenting a sensitivity of 76.6%. Notably, the mean SUVmax values for 68Ga-PSMA-11 PET/CT and 99mTc-HYNIC- PSMA-11 were comparable and a highly significant positive correlation (r > 0.93; p < 0.01) The average absorbed doses to the salivary glands, lungs, kidneys, urinary bladder, and liver were found to be comparable with 99mTc-MDP bone scanning. Conclusion The diagnostic performance of whole-body 99mTc-HYNIC PSMA-11 SPECT/CT is fairly comparable to 68Ga-PSMA PET/CT and offers a favorable dosimetry indicating its potential for PCa evaluation Advances in Knowledge 99mTc-PSMA-11 SPECT/CT may be an alternative and cost-effective tool for evaluation of initial PSMA disease burden as well as for response evaluation to PSMA targeted therapies