Comparison Between CT Volumetric Measurement and RECIST 1.1 Criteria to Assess the Tumoral Response in Advanced Renal Cell Carcinoma Treated by Immunotherapy

Objective: Assessment of a volumetric method versus gold standard unidimensional measurement based on RECIST 1.1 in advanced renal clear cell carcinoma (RCC) treated by immunotherapy. Materials and Methods: We retrospectively recorded the CT data of 14 adult patients treated with immunotherapy for metastatic RCC from February 2016 to January 2018. Follow-up CT scanners were independently reviewed by two radiologists. Unidimensional RECIST 1.1 and volumetric measurements were compared at each time point, with a total of 810 measurements performed for statistical analysis. The main criterion was the inter-observer agreement for each method. The secondary criterion was the tumoral response assessment based on three different items: RECIST 1.1, spherical volumetric method, ellipsoidal volumetric method. Results: Intraclass coefficient correlation in volumetric method (0.986 [95% CI: 0.980, 0.990]) was higher than in RECIST (0.903 [95% CI: 0.861, 0.928]). Relative measurement differences with Bland and Altman plot were lower in the volumetric method with shorter limits of agreement (0.8%; upper LOA95%: 36.5; lower LOA95%: −35), versus those in RECIST (-5.1 % (upper LOA95%: 46; lower LOA95%: −57). The volumetric method (especially the ellipsoidal one) assesses the progression disease earlier than RECIST for 57% of patients, but there is no formal difference for partial response assessment. Conclusion: Volumetric assessment for tumoral response in metastatic RCC compared to unidimensional measurements had a higher inter-observer agreement and might predict disease progression earlier.