Metastatic Diffusion Volume Based on Apparent Diffusion Coefficient as a Prognostic Factor in Castration‐Resistant Prostate Cancer

BACKGROUND Whole-body diffusion-weighted MRI (WB-DWI) is useful for assessing disease activity in castration-resistant prostate cancer (CRPC). MET-RADS-P is a subjective assessment-based reporting system proposed to standardize the interpretation of WB-DWI. However, a quantitative evaluation of WB-DWI has not been fully investigated. PURPOSE To investigate the validity, and analyze the prognostic value, of quantitative evaluation of WB-DWI based on apparent diffusion coefficient (ADC) values for CRPC. STUDY TYPE Retrospective. POPULATION Sixty-six patients with CRPC. The median age was 75 years. During the median follow-up period of 25.2 months, 23 of 66 patients (34.8%) died of prostate cancer. FIELD STRENGTH/SEQUENCE A 1.5 T WB-DWI was used with two b-values (0 s/mm2 -1000 s/mm2 ). A single-shot echo-planar imaging sequence was used. ASSESSMENT WB-DWI were evaluated by three readers according to MET-RADS-P scoring system. Using imaging software, Attractive BDScore, tumor diffusion volume (mDV) and ADC value of metastatic lesion (mADC) was calculated by two readers. The mDV was calculated with ADC values (×10-3 mm2 /sec) of 0.4-0.9 (mDV0.4-0.9 ), 0.9-1.4 (mDV0.9-1.4 ), and 1.4-1.8 (mDV1.4-1.8 ), respectively. STATISTICAL TESTS Spearman's rank correlation coefficient was used to assess the correlation. The relationships between the variables with cancer-specific survival (CSS) were evaluated. Multivariate analysis was performed using the Cox proportional hazards model. RESULTS mDVs showed a strong positive correlation with MET-RADS-P scores (r = 0.90/0.87, P < 0.05 for both). mDV showed a statistically significant association with CSS (hazard ratio [HR]: 1.01, P < 0.05). When the mDVs calculated based on the ADC values were included, mDV0.4-0.9 (HR: 1.02, P < 0.05) and the number of therapeutic lines (HR: 1.35, P < 0.05) were significant independent indicators of CSS shortening. CONCLUSION Assessment of metastatic tumor volume based on ADC values can be used in the prognostic evaluation of patients with CRPC. WB-DWI might be a potential prognostic imaging biomarker for CRPC. EVIDENCE LEVEL 4 TECHNICAL EFFICACY: Stage 2.