Reference dosimetry data and machine performance comparison for tomotherapy delivery systems audited by IROC

The aim of this work was to compare the imaging and radiation oncology core (IROC) on-site TomoTherapy dosimetry measurement results among institutions and generate a dataset of basic dosimetric properties for TomoTherapy units. Independent ion chamber measurements for nine TomoTherapy units were acquired by IROC physicists between 2008 and 2023. Measurements included percent depth dose (PDD) in a water tank and off axis factors (OAF) in a solid Polystyrene phantom. The independent measurements collected during the on-site audits for each TomoTherapy system were compared to corresponding TomoTherapy TPS calculations from the institution to assess agreement. Numeric measurement values and comparative ratios are compiled and tabulated according to measurement type (i.e., PDD and OAF). The distribution of the measurements was evaluated, and the mean, standard deviation of the mean, and median values are reported. These data provide an independent guide describing the inherent performance characteristics of TomoTherapy units. Such data may serve as a secondary check for users wishing to verify their beam model commissioning and ongoing quality assurance efforts.