3464 - The Relationship between Liver Metastasis Shrinkage Rate and Quantitative Values in Lu-177 DOTATATE Therapy for Somatostatin Receptor-Positive Neuroendocrine Tumors

Purpose/Objective(s): Lu-177 DOTATATE is a treatment for somatostatin receptor (SSTR)-positive neuroendocrine tumors (NETs). Among distant metastases in NETs, liver metastases are the most common, with reports indicating that 82% of patients with metastases have liver involvement. Our institution has implemented a SPECT/CT system from a technology company capable of quantitative evaluation and utilizes the imaging analysis software from a technology company to measure standardized uptake values (SUV) and radiation dose per unit volume (kBq/ml). This study aimed to analyze the relationship between the reduction of liver metastases and quantitative values in Lu-177 DOTATATE therapy for SSTR-positive NETs.

Materials/Methods: We analyzed nine patients with liver metastases from NETs who initiated and completed Lu-177 DOTATATE therapy between June 2022 and February 2024. Each patient received four cycles of 7.40 GBq at eight-week intervals in principle. Scintigraphy and SPECT/CT imaging were performed the day after each administration using Symbia Intevo 6. Using Syngo.via, we measured the volume of liver metastases, radiation dose (kBq/ml), and SUVmax at the first and fourth cycles of therapy.

Results: The median age of the 9 patients was 66 years, with three males and six females. NET grade was 2 in five cases, while it was unknown in four cases. One patient discontinued treatment after three cycles per personal request, while eight completed all four cycles. The median number of liver metastases was four (range: 2–8). For two cases with more than eight metastases, lesions appearing fused were counted as a single mass for quantitative assessment. Among the 35 measured liver metastases, 29 showed shrinkage or disappearance after treatment, while six progressed. The median reduction rates of kBq/ml and SUVmax in the shrinkage/disappearance group were 51.55% and 17.29% (p=0.02), and 51.83% and 20.66% (p=0.02), respectively, showing a significantly greater decrease compared to the progression group. The correlation coefficients between volume reduction rate and the decrease rates of kBq/ml and SUVmax were 0.722 and 0.693, respectively, indicating a strong correlation between quantitative reduction rates and volume reduction. Conversely, the median initial kBq/ml and SUVmax values were 836.92 vs. 319.94 (p=0.06) and 13.98 vs. 6.27 (p=0.06) in the shrinkage/disappearance and progression groups, respectively, suggesting a trend toward higher initial quantitative values in the shrinkage/disappearance group.

Conclusion: Liver metastases that showed shrinkage or disappearance had a tendency to exhibit higher initial quantitative values than those that progressed. These findings suggest that quantitative evaluation may serve as a potential predictor of therapeutic response in Lu-177 DOTATATE treatment.