Background: Quality Assurance (QA) in radiotherapy is an important studying issue in order to test the performance of medical Linac machine and verify the delivering accuracy of patient treatment plan.Aim of Study: Clinical validation of using compass system in VMAT QA for abdomen site pediatric patients.Material and Methods: Ten VMAT neuroblastoma plans were created using Monaco TPS.CT images, RT Structures, RT Plans, and RT doses for all cases were exported to COMPASS system through DICOM network then COMPASS computations were performed using collapsed cone algorism for all patients with a calculation grid resolution of 2mm from the imported DICOM RT plans. Finally, a comparison was performed based on dose difference and all VMAT plans were measured at two matched linear accelerators. Results:The mean dose of PTV and D99% for the ten cases were measured.The comparison between the Monaco dose calculation, compass computed dose and compass reconstructed dose showed a good agreement within maximum deviation 4% for the PTVs and critical organs in point doses and volume doses. Conclusions: Compass system is a reliable effective system to perform 3D dose verification of VMAT plans for neuroblastoma patients. So Compass QA system can be used as an effective tool before VMAT treatment. The variations of dose between TPS and Compass were due to mode of calculation (Compass algorism uses dose to water for calculation while Monte-Carlo algorism uses dose to medium).