RESUMEN
Objective The ionization chamber of ELEKTA medical linear accelerator monitoring is open to environmental factors such as temperature, air pressure, and humidity that may affect the stability of absolute dose output .The article aimed to ana-lyze the morning and evening absolute dose output stability at different energies of ELEKTA SYNERGY medical linear accelerator . Methods The absolute doses at different energies of medical linear accelerators were calibrated according to the IAEA TRS -277 re-port, and WI3 type solid water was used to perform repeated measurements in the morning and in the evening for 52 consecutive days under the same measurement conditions , during which a water tank measurement was conducted at random intervals per week to verify the accuracy of WI3 solid water measurements. Results The maximum deviation of WI3 solids water and tank measurement at all en -ergies was 0.5％ and the maximum deviations of daily energy stability at different energies were : -2.0％ (6MV), 1.9％ (15MV), 1.8％ (6MeV), -2.4％ (8MeV), -2.3％ (10MeV), -2.0％ (12MeV), 2.1％ (15MeV).The differences of 6MV, 15MV, 8MeV, and 10MeV energies in morning and evening paired t tests were statistically significant (P<0.05) without clinical significance, while no statistic significance was found in the differences of 6MeV, 12MeV, and 15MeV energies ( P >0.05). Conclusion Elekta Synergy medical linear accelerator shows excellent stability in absolute dose output.