Quantitative analysis of standardized uptake values (SUV) of metastatic bone lesions in scintigraphy with [99mTc]Tc-EDDA/HYNIC-Tyr3-octreotide in patients with neuroendocrine tumours.

Background: Neuroendocrine tumours (NETs) are a group of cancers that can produce hormones and other metabolically active compounds. The majority of NETs have specific tissue characteristics, such as the expression of somatostatin receptors (SSTR). Metabolic testing with [99mTc]Tc-EDDA/HYNIC-Tyr3-octreotide ([99mTc]Tc-EDDA/HYNIC-TOC) can be used in patients with NETs to visualize the presence of receptors in different locations of pathological lesions, including the skeletal system. The study aimed to calculate the body weight maximum standardized uptake value (SUVbwmax) of pathological bone lesions and healthy bone tissues, estimate the size of lesions, and identify a relationship between the SUVbwmax of the bone tissues, age and body mass of the study participants.

Material and methods: The somatostatin receptor scintigraphies (SRS) with [99mTc]Tc-EDDA/HYNIC-TOC were carried out at the Department of Nuclear Medicine, University Clinical Hospital No. 1, Pomeranian Medical University (PMU) in Szczecin from 2019 to 2022. Whole body and single photon emission computed tomography/computed tomography (SPECT/CT) scans were performed four hours after the injection of 700-800 MBq of [99mTc]Tc-EDDA/HYNIC-TOC in 344 patients with neuroendocrine tumours of various primary lesion locations. In 19 patients, who showed foci of increased radiopharmaceutical accumulation in bone location, the SUVbwmax was measured. The SUVbwmax of pathological bone lesions and healthy tissues were determined on SPECT/CT cross-sectional images using Xeleris 4 software.

Results: The total number of foci with increased SSTR expression in bone regions seen on scintigraphic images was 89. Among them, 32 bone lesions were visible on the corresponding CT scans. The mean SUVbwmax of these lesions was 31.39 [standard deviation (SD) 34.31]. For the other 57 lesions that were not visible on corresponding CT scans, the mean SUVbwmax was 19.12 (SD 24.24). The smallest bone lesion detected on the scintigram and visible on the corresponding CT location was 5 mm × 5 mm, measured in cross-section, and was located in the Th8 vertebral body; the largest, measuring 20 mm × 22 mm, was detected in the L3 vertebral body. The SUVbwmax of these lesions was 24.70 and 142.40, respectively.

Conclusions: Bone lesions seen on SPECT/CT in [99mTc]Tc-EDDA/HYNIC-TOC scintigraphy can be quantitatively analysed using the SUV index. Even a very small pathological bone lesion can be detected on [99mTc]Tc-EDDA/HYNIC-TOC scintigraphy. It was shown that in cases where bone lesions were visible on CT scans, the SUVbwmax of bone tumour lesions was higher than when lesions were not visible on CT. Body mass does not affect the SUVbwmax of bone lesions. SUVbwmax of healthy bone tissue decreased with age.