To date, several 99mTc-labelled PSMA inhibitors have been developed for PCa detection, including 99mTc-MIP-1404
. Compared with other imaging techniques, such as CT and MRI, SPECT/CT using 99mTc-labelled PSMA has demonstrated great potential for detecting PCa metastasis and guiding the treatment of targeted lesions, thus benefiting patients[7,10]
The present study conducted a clinical safety evaluation of 99mTc-HYNIC-PSMA according to a method that we developed
. Our results suggest that 99mTc-HYNIC-PSMA was excreted mainly through the urinary system and that its absorbed doses in organs, including the brain and heart, were low. The kidneys showed the highest absorbed dose, which had a value of 2.87E-02±1.53E-03 mGy/MBq. In other organs, including the red bone marrow, thyroid and adrenal gland, the absorbed doses were lower. The effective dose of 99mTc-HYNIC-PSMA was 3.72E-03±4.50E-04 mSv/MBq, so it is 2.75±0.33 mSv when the administered activity was 740 MBq. This effective dose value is similar to that of 99mTc-EDDA/HYNIC-iPSMA
(3.73E-03 mSv/MBq) but lower than that of 99mTc-MIP-1404
(8.8E-03 mSv/MBq) and 99mTc-MIP-1405
(7.9E-03 mSv/MBq). The total effective dose in the body is also much lower than that of 68Ga-labelled and 18F-labelled PSMA-targeted tracers, including 68Ga-PSMA-11
(2.36E-02 mSv/MBq), 68Ga-PSMA-617
(2.1E-02 mSv/MBq), 18F-PSMA-1007
(2.2E-02 mSv/MBq) and 18F-DCFPyL
(1.39E-02 mSv/MBq). This is because 68Ga and 18F have a dual-photon property and emit gamma radiation with higher energy than 99mTc. Furthermore, the effective dose of 99mTc-HYNIC-PSMA is also lower than that of conventional 99mTc-labelled radiopharmaceuticals used in SPECT/CT scans, such as MDP (5.68E-03 mSv/MBq)
and MIBI (7.83E-03 mSv/MBq)
. Of note, because the main excretory pathways for the tracer are the kidneys and bladder, which is in agreement with the results shown in our current study, we suggest that patients drink plenty of water or take diuretics after the scan to reduce the absorbed dose.
The Dosimetry Toolkit supports 3 different scenarios, including multiple whole-body SPECT/CT scenarios,
multiple whole-body planar scenarios and a hybrid planar-SPECT/CT scenario. In order to avoid the long scan
time required by multiple whole-body SPECT imaging, which could cause tracer metabolic difference between segments for each scan, the hybrid imaging scenario was chosen. Conventionally, for organ segmentation, it is
very difficult to manually utilize information from 2D planar images, particularly for those regions with low tracer uptake. Unlike the conventional technique, this computer-assisted semiautomatic method provides a more consistent and convenient method for image processing.
For the tracer imaging feasibility study, Table 3 showed that the 99mTc-HYNIC-PSMA was able to be accumulated at primary lesion sites and metastatic lesion sites (bone, soft tissue and lymph nodes). The average
tumor-to-background ratio for 99mTc-HYNIC-PSMA at 2 h was 9.42 2.62, which is moderately higher than
that observed for 99mTc-MIPs (range 3.8–6.2)
. When the PSA is very low (Patient #3 from Table 3 as an example, with PSA of only 0.56), the 99mTc-HYNIC-PSMA image can detect the uptake of the malignant lesion, while the anatomical imaging of the patient did not show any corresponding lesions (Fig. 4).