Rationale and Objectives: Magnetic resonance (MR) imaging is used to assess brain tumor response to therapies and a MR quality assurance program is necessary for multicenter clinical trials employing imaging. This study was performed to determine overall variability of quantitative image metrics measured with the American College of Radiology (ACR) phantom among 11 sites participating in the Pediatric Brain Tumor Consortium (PBTC) Neuroimaging Center (NIC) MR quality assurance (MR QA) program.Materials and Methods-An MR QA program was implemented among 11 participating PBTC sites and quarterly evaluations of scanner performance for seven imaging metrics defined by the ACR were sought and subject to statistical evaluation over a 4.5 year period. Overall compliance with the QA program, means, standard deviations and coefficients of variation (CV) for the quantitative imaging metrics were evaluated.Results-Quantitative measures of the seven imaging metrics were generally within ACR recommended guidelines for all sites. Compliance improved as the study progressed. Inter-site variabilities as gauged by coefficients of variation (CV) for slice thickness and geometric accuracy, imaging parameters that influence size and/or positioning measurements in tumor studies, were on the order of 10 % and 1% respectively. Conclusion-Although challenging to establish, MR QA programs within the context of PBTC multi-site clinical trials when based on the ACR MR phantom program can a) indicate sites performing below acceptable image quality levels and b) establish levels of precision through instrumental variabilities that are relevant to quantitative image analyses, e.g. tumor volume changes.