Comparing Response Evaluation Methods for PRRT in Neuroendocrine Tumors: Insights from an Exploratory Study

Area of Science:

• Oncology
• Nuclear Medicine
• Radiology

Background:

• Assessing treatment response in neuroendocrine tumors (NETs) is complex, especially after peptide receptor radionuclide therapy (PRRT) due to its multifactorial mechanism and lack of standardized criteria.
• Accurate response evaluation is crucial for guiding further treatment and predicting patient outcomes.

Purpose of the Study:

• To compare various imaging-based response assessment methods following PRRT in NET patients.
• To explore the relationship between these assessment methods and clinical outcomes, specifically progression-free survival (PFS).

Main Methods:

• Retrospective analysis of 31 NET patients treated with PRRT, who underwent [68Ga]Ga-DOTATOC PET/CT before and after therapy.
• Evaluation of five response criteria: Krenning Score, adapted PERCIST (MORE), ZP-normalized parameter, qualitative visual PET assessment, and RECIST-based CT response.
• Correlation of imaging findings with clinical outcomes using nonparametric analyses.

Main Results:

• Response rates varied significantly across methods: functional imaging (MORE 66%, Visual PET 68%, ZP 70%) showed higher rates than RECIST (40%) and Krenning score (21%).
• After a median follow-up of 37 months, 58% of patients progressed.
• No statistically significant association was found between response criteria and progression, though functional imaging demonstrated a trend towards better correlation with longer PFS.

Conclusions:

• Functional PET-based response criteria may correlate with progression-free survival in NET patients treated with PRRT, potentially outperforming RECIST and Krenning scores.
• These findings are exploratory and hypothesis-generating due to study limitations, and do not provide definitive evidence for practice change.