A Comprehensive Quality Assurance Program of Small Animal Irradiators for Preclinical Radiation Research

Abstract

Draeger et al. (Red Journal, 2020) raised awareness on the importance of the standardization of dosimetry protocols in pre-clinical radiobiology research and the inclusion of physicists on the research team. At our institute, a QA program of the small animal radiation research platform (SARRP, Xstrahl) that includes daily, monthly and annual tests have been implemented to ensure minimal delivery uncertainties. Details of the QA procedures, feasibility and results will be reported. End-to-end imaging and radiation isocenter coincidence testing using a Winston-Lutz phantom and EBT3 films, as well as CBCT imaging quality visual check, were performed daily by the research team. Monthly QA (mechanical and dosimetric tests such as the star-shot test and output constancy of the reference field), and annual QA (TG61 absolute dosimetry, imaging quality phantom check, output factor, beam profiles and percent depth dose measurements) were performed by the physics staff. The estimated time to complete the daily, monthly and annual tests were twenty minutes, one and two hours, respectively. The frequency of each QA item had been established based on the failure occurrence rate. The tolerance results of the daily, monthly and annual testing are displayed in the table. The results of the daily isocenter coincidence check show a discrepancy between the radiation isocenter and set-up center combined with the uncertainty from the couch movement of the image-guided system smaller than 1.5 mm. This test has successfully caught failures in the entire delivery process. For the monthly QA, diameter of the radiation isocenter was consistently smaller than 0.5 mm and the output has been measured to be within ±1% of baseline. The results of the annual QA, using an ion chamber and EBT3 films, match the beam data of the treatment planning system as well as the data from our in-house Monte Carlo calculation within the tolerance. Additionally, we used EBT3 films and a mouse solid water phantom as tools for verification of dosimetrically complex plans. The maximum dosimetry error observed has been consistently within 2%. With the implemented QA program, the fidelity of overall system delivery was ensured for robust and accurate small animal radiation studies without excess burden on the medical physicists and research team.Tabled 1Abstract 2596; TableProcedureToleranceDailyEnd to end imaging and radiation isocenter coincidence2 mmCBCT imaging quality visual checkBaselineLocalizing lasers1 mmMonthlyOutput constancy2%Isocentricity1 mmGantry position check1 mmAnnualOutput, flatness and symmetry, PDD, output factor1%CBCT imaging quality phantom checkBaseline Open table in a new tab