[99mTc]Tc-iPSMA SPECT/CT as an alternative to PET imaging for decision making in prostate cancer patients.

Abstract

34 Background: Prostate cancer represents a strong economic and social burden in the world. Imaging, pathology report and prostate specific antigen are the cornerstone for decision making. PSMA imaging with PET/CT has demonstrated superiority over conventional imaging, however, its availability is limited in countries with emerging economies. 99mTc-based imaging is widely used and has been favored by the development of new inhibitors targeting PSMA. Methods: We analyzed retrospectively 119 men with a histopathological diagnosis of prostate cancer obtained through transrectal biopsy or with clinical suspicion due to elevated PSA levels and physical examination findings. 68 were classified as high-risk and 51 as very high-risk, and referred for staging with [99mTc]Tc-iPSMA SPECT/CT between July 2022 and July 2024. The waiting times for initiating treatment were compared with a strategy based on PET/PSMA. Also number of lesions in patients with dual imaging with [99mTc]Tc-MDP and [99mTc]Tc-iPSMA was analyzed and assessed the changes in intention to treat. Results: Mean age of patients was 69.2 y/o (range 55-89 y/o), mean PSA level of staging group was 78.5 ng/mL (range 28.5-1667 ng/mL). Waiting time for a [99mTc]Tc-iPSMA was 7.2 days (+/- 1.5 days) versus 67.5 days (+/- 11.8 days) for [18F]F-iPSMA PSMA-1007. An additional study was required in 15.1% (n=18) of patients (n=13 PET/CT [18F]F PSMA-1007, 5 abdominal magnetic resonance). 36 patients had dual studies, observing 108 lesions with [99mTc]Tc-iPSMA and 114 with [99mTc]Tc-MDP, 6 with PSMA and 12 with MDP did not show anatomical changes. These findings did not modify the clinical stage or treatment intention. Overall, 590 lesions were identified in 119 patients, 101 in prostate, 267 in bone (diffuse disease in bone was considered as a single lesion), 135 in regional lymph nodes, and 87 in non-regional lymph nodes. Size range of lymph nodes detected were 0.5 mm to 25 mm. The change in management occurred in 23% patients (n=28); the changes were from ADT alone to doublet (ADT and Docetaxel) (n=11), from Radiotherapy to the pelvis to ADT + Docetaxel (n=8), from Radiotherapy to the pelvis to triplet (ADT+ Docetaxel + ARPi) (n=5), from ADT + RT to surgery (n=2), from ADT alone to ADT + SBRT (n=2). Conclusions: [99mTc]Tc-iPSMA SPECT/CT is an efficient alternative tool to [18F]F-iPSMA PSMA-1007, the results provide sufficient information to allow a significant change in intention to treat, significantly reducing waiting times, especially in countries where equipment availability PET is limited. These results support the development of public policies that promote the use of this type of radiopharmaceuticals to expand access to the new generation imaging modality and provide a benefit in the clinical management of prostate cancer especially in countries with low PET/CT infrastructure.