Interrater reliability of Brain Tumor Reporting and Data System (BT-RADS) in the follow up of adult primary brain tumors: a single institution experience in Italy.

Background: In 2018, a new system was proposed for classifying and reporting post-treatment adult brain tumor on magnetic resonance imaging, named as Brain Tumor Reporting and Data System (BT-RADS), that needs a validation by means of agreement studies. Methods: A retrospective study was designed with the aim of identifying contrast-enhanced magnetic resonance imaging (MRI) of adult patients on follow-up for primary brain tumor at Fondazione Policlinico Campus Bio-Medico. Four radiologists (2 radiology residents, 1 general radiologist, 1 neuroradiologist) read and scored each study using the BT-RADS scoring tool, blinded to the MRI original report. Interobserver agreement and Fleiss' k were calculated to assess the level of diagnostic agreement. It was assessed how many times the assignment of different scoring of BT-RADS would have led to a different patient management. Results: The total number of patients included in the study was 23 with 147 MRIs and a total of 588 BT-RADS scores retrospectively evaluated. The two most frequent tumor types were astrocytoma grade 4 (62%) and oligodendroglioma grade 3 (21%). The overall agreement rate for all 4 radiologists was 82% with a Fleiss' k of 0.70. The overall agreement rate between general radiologist and neuroradiologist was 91% with a Fleiss' k of 0.86. The overall agreement rate between 2 radiology residents and neuroradiologist was 80% with a Fleiss' k of 0.66. Astrocytoma grade 3 (k: 0.51) and oligodendroglioma grade 2 (k: 0.32) showed a poor agreement while higher values of agreement were found for astrocytoma grade 4 (k: 0.70), astrocytoma grade 2 (k: 0.78) and oligodendroglioma grade 3 (k: 0.78). All the radiologists agreed on BT-RADS assignment in 70% patients, three radiologists agreed in 17% and two radiologists agree in 13%. In no cases there was a complete disagreement among the readers. In 18% of cases the discrepancy in the estimated BT-RADS would have led to a different follow-up management. Conclusions: BT-RADS can be considered a valid tool for neuroradiologists and radiologists even with little experience in the interpretation of patients' images during follow-up for adult primary brain tumors supporting standardized interpretation, reporting and clinical management.