Standardized Uptake Values on SPECT/CT: A Promising Alternative Tool for Treatment Evaluation and Prognosis of Metastatic Neuroendocrine Tumours

Abstract

(1) Background: The aim of our study was to assess the feasibility of 99mTcEDDA/HYNIC-TOC SPECT/CT quantitative analysis in evaluating treatment response and disease progression in patients with NETs. (2) Methods: This prospective monocentric study evaluated 35 SPECT/CT examinations performed on 14 patients with neuroendocrine tumours who underwent a baseline and at least one follow-up 99mTcEDDA/HYNIC-TOC scan as part of their clinical management. The examination protocol included a whole-body scan acquired 2 h after the radiotracer’s administration, with the SPECT/CT performed 4 h post-injection. Images were analyzed by two experienced physicians and patients were classified into response categories based on their changes in SUV values. (3) Results: We evaluated 14 baseline studies and 21 follow-up scans, accounting for 123 lesions. A statistically positive correlation has been found between the SUVmax and SUVpeak values in tumoral lesions (p < 0.05). No correlation has been found between the SUV values and the ki67 proliferation index. Finally, 64.29% patients were classified as SD at the end of the study, with only 14.29% of patients exhibiting PD and 21.43% patients with PR. (4) Conclusions: The quantitative analysis of 99mTcEDDA/HYNIC-TOC SPECT/CT data in patients with neuroendocrine tumours could represent an alternative to 68Ga-DOTA-peptides PET/CT for the monitoring and prognosis of NETs.

Keywords: 68Ga-DOTA-PET/CT; 99mTcEDDA/HYNIC-TOC; SPECT/CT; metastatic disease; neuroendocrine tumors; quantitative SPECT/CT; somatostatin receptors.

Figure 1

Correlation between SUV_max and SUV_peak values in NET lesions.

Figure 2

Patient distribution after follow-up examinations. Abbreviations: PD—progressive disease; PR—partial response; SD—stable disease.

Figure 3

Comparison between a baseline and a follow−up scan of a 56−year−old male patient, diagnosed with an intestinal NET, grade G1, with hepatic, lymphatic and osseous metastases. The patient had been following treatment with long acting SSA. Although the liver metastasis and the paratraheal and celiac lymph nodes presented a notable increase in ^99mTc−EDDA/HYNIC−TOC uptake, the final assessment of the follow-up study established that the patient had stable disease (SD).

Figure 4

Comparison between a baseline and a follow-up scan of a 69−year−old female patient suffering from pancreatic NET, treated with long acting somatostatin analogues. The comparative analysis between the baseline scan and the follow−up scan (a) shows a decrease in uptake both in the primary tumour (the pancreas) and in the liver metastasis. However, when analysing the two lesion segmentation processes separately, compared to the baseline scan (b), the follow−up scan (c) shows that new lesions developed in the lymph nodes and bones. This patient was finally classified as PD.

Figure 4

Comparison between a baseline and a follow-up scan of a 69−year−old female patient suffering from pancreatic NET, treated with long acting somatostatin analogues. The comparative analysis between the baseline scan and the follow−up scan (a) shows a decrease in uptake both in the primary tumour (the pancreas) and in the liver metastasis. However, when analysing the two lesion segmentation processes separately, compared to the baseline scan (b), the follow−up scan (c) shows that new lesions developed in the lymph nodes and bones. This patient was finally classified as PD.