Volumetry: an alternative to assess therapy response for malignant pleural mesothelioma?

The purpose of our study was to assess robustness of volumetric measurement of malignant pleural mesothelioma (MPM) before and after chemotherapy to modified RECIST (response evaluation criteria in solid tumours) criteria. 30 patients with digitally available chest computed tomography (CT) scans before and after three cycles of chemotherapy were included. Three readers independently assessed tumour response using two different methods: 1) the modified RECIST criteria; and 2) the tumour volumetric approach using dedicated software (Myrian; Intrasense, Paris, France). Inter-rater reliability of unidimensional and volumetric measurements was assessed using intraclass correlation. Tumour response classification for modified RECIST was compared to the volumetric approach applying unidimensional RECIST volumetric equivalent criteria. The determination of unidimensional tumour measurement (RECIST) revealed a low inter-rater reliability (0.55) and a low interobserver agreement for tumour response classification (general κ 0.33). Only 14 patients were classified equally. A high inter-rater reliability (0.99) and interobserver agreement (general κ 0.9) were found for absolute tumour volumes (volumetric measurements). 27 cases were classified equally. The number of cases classified as "stable disease" was higher for the volumetric approach using tumour-equivalent criteria compared to modified RECIST. Volumetric measurement of MPM on CT using Myrian software is a reliable, reproducible and sensitive method to measure tumour volume and, thus, therapy response after induction chemotherapy.