Integrating DWI Parameters with RECIST 1.1 for Early Assessment of Systemic Therapy Response in Lung Cancer Pelvic Bone Metastases

OBJECTIVES: To determine preliminary quantitative ADC thresholds for functional response and to evaluate whether integrating DWI metrics with RECIST 1.1 provides complementary information for early systemic therapy response assessment in bone metastases. METHODS: This retrospective single-centre study included lung cancer patients with pelvic bone metastases who underwent three MRIs between November 2015 and November 2023: baseline, early time point (<4 months, TP1), and late (6-15 months, TP2) time points. ROC analysis based on lesion size change at TP2 determined ADC thresholds defining DWI response. A DWI response was defined as ADC >1300 µm²/s or ΔADC >0.14. An integrated response scheme (DWI-RECIST) combined this DWI-based response with RECIST assessment. Early responses at TP1 were compared between RECIST and DWI-RECIST using RECIST at TP2 as reference standard. Interobserver agreement was assessed using intraclass correlation coefficient, and diagnostic performance was evaluated using net reclassification improvement and AUCs. RESULTS: Seventy-eight lesions from 27 patients were included. Compared with RECIST, DWI-RECIST yielded net classification gains of 7.4% (reader 1) and 11.1% (reader 2). DWI-RECIST showed higher AUCs than RECIST (reader 1: 0.6964 vs. 0.6184, p = 0.472; reader 2: 0.6415 vs. 0.6184, p = 0.781). Interobserver agreement for ADC was good (ICC 0.83-0.86). CONCLUSIONS: Integrating ADC-derived DWI metrics with RECIST 1.1 may provide complementary information for early assessment of pelvic bone metastases from lung cancer, particularly in lesions categorised as stable disease. ADVANCES IN KNOWLEDGE: This pilot study proposes quantitative ADC thresholds and introduces a framework integrating these with RECIST 1.1 to support more objective response assessment in lung cancer pelvic bone metastases.