Sequential dual-energy CT for longitudinal assessment of pathologic response to neoadjuvant immuno-chemotherapy in locally advanced gastric cancer.

[OBJECTIVES] To longitudinally evaluate pathologic response outcomes after neoadjuvant immuno-chemotherapy (NICT) for patients with locally advanced gastric cancer (LAGC) using pre- and post-treatment dual-energy CT (DECT).

[MATERIALS AND METHODS] Between Jan 2021 and Dec 2023, 115 patients who underwent NICT plus gastrectomy and triple-phase enhanced DECT scans before and after NICT were retrospectively enrolled. Pathologic tumor regression grade (TRG) was the reference standard, patients were labelled as responders (TRG = 0 + 1) and non-responders (TRG = 2 + 3) accordingly. A two-dimensional free-hand region of interest method was adopted to obtain the iodine concentration (IC) values. Pre- and post-NICT IC and normalized IC (nIC) were measured at arterial/venous/delay phase (AP/VP/DP), respectively; their changes [ΔIC (%)] defined as (IC_post-IC_pre)⁄IC_pre × 100% were calculated. Pre- and post-NICT imaging parameters and their changes were compared between different response groups. Non-responders' associated parameters were selected using multivariable logistic regression analysis. Their performances were analyzed by the area under the receiver operating characteristic curve (AUC). Their associations with patient survival were explored by using Kaplan-Meier survival analysis.

[RESULTS] ICDP-pre, ΔICAP, thickness-post with cut-off value of > 2.306 mg/mL, ≤ 26.70%, > 18.5 mm, respectively, indicates non-responders with equivalent AUC being 0.616 (95% CI: 0.521-0.705), 0.625 (95% CI: 0.529-0.713), and 0.660 (95% CI: 0.565-0.745). Their combination demonstrated an improved AUC of 0.774 (95% CI: 0.686-0.846) and was associated with patient disease-free survival (DFS) with a hazard ratio being 2.239 (95% CI: 1.004-4.991) (p = 0.026).

[CONCLUSION] Pre- and post-NICT DECT-based quantifications are useful for longitudinal assessment of pathologic response outcomes after NICT in LAGC. ICDP-pre, ΔICAP, and thickness-post are equally useful, their combination demonstrated incremental benefit.

[KEY POINTS] Question Accurate evaluation of the efficacy of NICT in patients with LAGC remains challenging due to the lack of effective biomarkers. Findings Sequential DECT-based ICDP-pre, ΔICAP, and tumor thickness-post were predictive of TRG status. Their combination demonstrated enhanced performance and was associated with patient DFS. Clinical relevance DECT represents a promising imaging technique with added advantages for longitudinal assessment of pathologic response to NICT in LAGC, potentially facilitating more personalized treatment strategies among this population.