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/mm 2 –1000 s/mm 2 ). 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 mm 2 /sec) of 0.4–0.9 (mDV 0.4–0.9 ), 0.9–1.4 (mDV 0.9–1.4 ), and 1.4–1.8 (mDV 1.4–1.8 ), 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, mDV 0.4–0.9 (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