Inflammatory and immune marker dynamics following intratumoral alpha dart for pancreatic cancer.

771 Background: Immune markers such as neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and systemic inflammatory index (SII; NLR*platelet) are adverse prognostic factors in pancreatic ductal adenocarcinoma (PDAC). External beam radiotherapy (EBRT) and stereotactic body radiotherapy (SBRT) have limited role in PDAC and are known to typically worsen these inflammatory indices via radiation-induced lymphopenia. Diffusing Alpha-emitters Radiation Therapy (Alpha DaRT) delivers highly localized intratumoral alpha radiation with minimal systemic exposure. Whether Alpha DaRT alters systemic inflammatory markers in PDAC remains unknown. Methods: In a pilot analysis of 32 PDAC patients treated with EUS-guided intratumoral Alpha DaRT (NCT04002479), 23 with complete laboratory data were analyzed. Demographics, baseline and 30-day post-treatment hematologic and immune markers (SII, NLR, PLR, IL-6, CD4/CD8 ratio, CRP) were collected. Pre- vs post-treatment medians were compared using Wilcoxon signed-rank tests. Logistic regression evaluated baseline, post-treatment, and delta (Δ) NLR/PLR for association with disease control (DC = CR/PR/SD) vs progression (PD). Results: Median age was 73 years (40–91); 8 men (34.8%), 15 women (65.2%). All patients had successful source placement. Median pre- vs post-treatment values: NLR 3.0 vs 3.1 (p=0.22), PLR 127.1 vs 125.0 (p=0.82), IL-6 614.0 vs 5.9 pg/mL (p