Prognostic value of interim [⁶⁸Ga]Ga-DOTA-TOC PET/CT in patients with neuroendocrine tumour who underwent peptide receptor radionuclide therapy

Objectives: This study evaluated the prognostic value of basal and interim [⁶⁸Ga]Ga-DOTA-TOC PET/CT in patients with locally advanced or metastatic neuroendocrine tumour (NET) who received peptide receptor radionuclide therapy (PRRT).

Methods: Patients with NET who received PRRT with [¹⁷⁷Lu]Lu-DOTA-TATE at our institution were retrospectively reviewed. Among them, patients who underwent both basal and interim (after two cycles of PRRT) [⁶⁸Ga]Ga-DOTA-TOC PET/CT were included. Alongside clinicopathologic parameters, PET parameters of maximum standardised uptake value (SUVmax), tumour-to-liver ratio (TLR), whole tumour volume (WTV) and total receptor expression (TRE: WTV multiplied by mean standardised uptake value) were obtained from basal and interim [⁶⁸Ga]Ga-DOTA-TOC PET/CT, and their proportional changes (∆) were assessed for associations with progression-free survival (PFS) using Kaplan-Meier analysis, log-rank tests, and a Cox proportional-hazards regression model.

Results: Twenty-four patients were finally included (10 men and 14 women, median age of 56.5 years, age range 32-74 years). Among them, 16 patients (66.7%) experienced disease progression. In univariate analysis, high ∆WTV (≥ -10%, hazard ratio [HR] = 3.053 [1.003-9.289], p = 0.049) and high ∆TRE (≥ -21%, HR = 3.567 [1.144-11.122], p = 0.028) were significantly associated with shorter PFS. In multivariate analyses adjusted for WHO grade, high ∆WTV (HR = 3.345 [1.055-10.601], p = 0.043) and high ∆TRE (HR = 3.894 [1.194-12.695], p = 0.024) were significant predictors of shorter PFS.

Conclusion: The study demonstrates that basal and interim [⁶⁸Ga]Ga-DOTA-TOC PET/CT scans, through proportional changes in WTV and TRE, effectively predict PFS in neuroendocrine tumour patients receiving PRRT.

Key points: Question Peptide receptor radionuclide therapy is utilised for patients with somatostatin receptor-positive well-differentiated neuroendocrine tumours; however, prognostic predictors are not well established. Findings Progression-free survival was significantly associated with the proportional change in whole tumour volume and total receptor expression between basal and interim [⁶⁸Ga]Ga-DOTA-TOC PET/CT. Clinical relevance Interim [⁶⁸Ga]Ga-DOTA-TOC PET/CT can serve as a valuable imaging method to predict prognosis of peptide receptor radionuclide therapy.