PURPOSE In abdominal radiotherapy inconsistent interfraction respiratory motion can result in deviations during treatment from what was planned in terms of target position and motion. Audiovisual biofeedback (AVB) is an interactive respiratory guide that produces a guiding interface that the patient follows over a course of radiotherapy to facilitate regular respiratory motion. This study assessed the impact of AVB on interfraction motion consistency over a course of liver cancer SBRT. METHODS Five liver cancer patients have been recruited into this study, 3 followed AVB over their course of SBRT and 2 were free breathing (FB). Respiratory signals from the Varian RPM were obtained during 4DCT and each treatment fraction. Respiratory signals were organized into 10 respiratory bins, and interfraction consistency was quantified by the difference between each treatment fraction respiratory bin and each respiratory bin from 4DCT. Interfraction consistency was considered as both the relative difference (as a percentage) and absolute difference (in centimeters) between treatment respiratory bins and 4DCT respiratory bins. RESULTS The relative difference between 4DCT and treatment respiratory bins was 22 ± 16% for FB, and 15 ± 10% for AVB, an improvement of 32% (p < 0.001) with AVB. The absolute difference between 4DCT and treatment respiratory bins was 0.15 ± 0.10 cm for FB, and 0.14 ± 0.13 cm for AVB, an improvement of 4% (p = 0.6) with AVB. CONCLUSION This was the first study to compare the impact of AVB breathing guidance on interfraction motion consistency over a course of radiotherapy. AVB demonstrated to significantly reduce the relative difference between 4DCT and treatment respiratory motion, but the absolute differences were comparable, largely due to one AVB patient exhibiting a larger amplitude than the other patients. This study demonstrates the potential benefit of AVB in reducing motion variations during treatment from what was planned. Paul Keall, Sean Pollock, Ricky OBrien and Kuldeep Makhija are shareholders of Respiratory Innovations, an Australian company that is developing a device to improve breathing stability. No funding or support was provided by Respiratory Innovations. Paul Keall is one of the inventors of US patent # 7955270.