Biodistribution and Semiquantitative Analysis of ^99mTc-HYNIC-PSMA-11in Prostate Cancer Patients: A Retrospective...

To emphasize the feasibility of imaging prostate cancer patients under SPECT/CT with ^99mTc-HYNIC-PSMA-11 and evaluate the possibility in clinical application for screening patients for radioligand therapy, with the help of SUV-based biodistribution mapping.

In context to prostate specific membrane antigen's (PSMA) overexpression in prostate cancer cells there has been a gradual increase in imaging prostate cancer, currently the second leading cause of cancer deaths in males and the sixth cause of cancer death worldwide, with the help of radiolabeled PSMA small molecule inhibitors over the past few years. Of the two modalities under Nuclear Medicine facility (positron emission tomography/CT [PET/CT] and single photon emission CT [SPECT/CT]), though PET/CT has high sensitivity for tumor sites, even at low PSA level less however, the availability of 18F based radiotracer for PET imaging necessitates the dependency on a cyclotron in the near vicinity for production or regular supply. Another option of Germanium 68/ Gallium 68 generator (⁶⁸Ge/⁶⁸Ga generator) can be explored but the cost involved becomes a limitation. These challenges led to the exploration of an alternative to help cater the needs of society with ^99mTc labeled PSMA inhibitor, which is very easily available and a cost effective solution for imaging prostate cancer workup.

A retrospective analysis was conducted on 39 patients who had undergone ^99mTc-HYNIC-PSMA-11 study over a period of 6 months. The patients were further categorized based on spread of disease and divided in two categories: localized disease and oligometastatic disease. Imaging was done under Discovery NM/CT 670 DR model SPECT/CT. The planar and SPECT/CT images were analyzed using Xeleris DR Functional imaging (Version 4.1) workstation under Q. Volumetric MI evolution for oncology software and maximum and mean standardized uptake value (SUV_max, SUV_mean) were determined on skeletal and soft tissue regions for both the categories (localized and oligometastatic). Further, statistical analysis was conducted through an independent samples t-test to find the significance, if any.

The biodistribution of ^99mTc- HYNIC-PSMA-11 showed high uptake in parotid gland, submandibular gland, kidneys and urinary bladder, of which kidneys showed the highest uptake in all the scans. The SUV_max and SUV_mean comparison between localized and oligometastatic condition for various body regions did not show any statistically significant differences as indicted by the p-value.

The biodistribution of ^99mTc- HYNIC-PSMA-11 is similar to 68Ga-PSMA-11 scan, hence can be used as a cost-effective alternate for imaging overexpression of PSMA in case of prostate cancer patients.