Multi-institutional comparison of secondary check of treatment planning using computer-based independent dose calculation for non-C-arm linear accelerators

•This is the first multicenter study of secondary plan checks for non-C-arm linacs.•A total of 973 CyberKnife, Vero4DRT, and TomoTherapy treatment plans were assessed.•A 5% difference in the check is feasible as an action level for non-C-arm linacs.•A 3–4% systematic difference in the check is apparent in heterogeneous conditions. This report covers the first multi-institutional study of independent monitor unit (MU)/dose calculation verification for the CyberKnife, Vero4DRT, and TomoTherapy radiotherapy delivery systems. A total of 973 clinical treatment plans were collected from 12 institutions. Commercial software employing the Clarkson algorithm was used for verification after a measurement validation study, and the doses from the treatment planning systems (TPSs) and verification programs were compared on the basis of the mean value ± two standard deviations. The impact of heterogeneous conditions was assessed in two types of sites: non-lung and lung. The dose difference for all locations was 0.5 ± 7.2%. There was a statistically significant difference (P