Lesion-level Quantitative Post-therapy SPECT/CT During ¹⁷⁷Lu-DOTATATE PRRT for NET Liver Metastases

Quantitative post-therapy single-photon emission computed tomography/computed tomography (SPECT/CT) may offer valuable insights for response assessment during peptide receptor radionuclide therapy (PRRT), but lesion-level evidence for liver metastases from neuroendocrine tumors (NETs) remains limited. This study assessed lesion-level longitudinal changes in practical quantitative indices, including kBq/ml max and maximum standardized uptake value (SUVmax), during ¹⁷⁷Lu-DOTATATE PRRT and their association with CT-based volumetric change.

This retrospective single-center study included 12 patients with NETs (51 liver metastases) treated with ¹⁷⁷Lu-DOTATATE PRRT. Quantitative SPECT/CT was performed the day after each cycle. SUVmax and kBq/ml max were measured for each lesion, and tumor volume was assessed using the CT component. Baseline (post-cycle 1) and final-cycle values were recorded. Lesions were classified as non-progressive (shrinkage/disappearance/stable) or progressive based on CT volumetric change. Spearman's rank correlation, the Wilcoxon signed-rank test, and the Mann-Whitney U-test were used.

Eleven patients completed four cycles and one discontinued after three cycles. Lesion volume, kBq/ml max, and SUVmax significantly decreased from baseline to final evaluation (all p<0.01). Of 51 lesions, 39 were non-progressive and 12 were progressive. Percentage reductions in kBq/ml max and SUVmax were strongly correlated with volumetric shrinkage (ρ=0.757 and 0.734). Non-progressive lesions showed greater reductions in both indices than progressive lesions (both p<0.01). Baseline kBq/ml max and SUVmax were higher in non-progressive lesions (p=0.029 and 0.030).

In this exploratory lesion-level analysis for NET liver metastases, post-therapy quantitative SPECT/CT metrics (kBq/ml max and SUVmax) were associated with CT-based volumetric change during ¹⁷⁷Lu-DOTATATE PRRT.