To address the efficacy and safety of [177Lu]DOTATATE peptide receptor radionuclide therapy (PRRT) for peritoneal carcinomatosis/mesenteric fibrosis (PC/MF) with reference to liver metastases through sequential [68Ga]DOTATOC PET/CT in patients with small-intestine neuroendocrine tumors (SiNETs).

Twenty patients underwent [68Ga]DOTATOC PET/CT before PRRT (PETbefore), after two cycles (PETinterim), and at the end of treatment (PETend). SUVmax and functional volumes were measured in target lesions. Digestive complications were recorded, and functional Objective Response Rate (fORR) assessed.

Seventeen patients presented with PC, one with both MF and PC, and two with MF only. Eight patients were classified as high-risk, and 12 as risk for intestinal obstruction. PC/MF functional volumes remained unchanged after treatment, with modest SUVmax decrease, while liver lesions showed marked functional volume reduction and greater SUVmax decrease. This divergence was evident after the first two cycles, indicating limited PC/MF response. Similar significant results were obtained considering only the 18 patients with PC. PC/MF showed a trend toward a lower fORR than liver lesions (18.7% vs. 38.4%), with 15% of patients experiencing obstruction within three months post-PRRT.

PC/MF exhibit increased resistance to [177Lu]DOTATATE PRRT compared to liver metastases, with non-negligible risk of obstruction occurring within three months after PRRT, particularly in patients with extensive peritoneal disease.