PURPOSE/OBJECTIVE(S): Motion management is crucial to safe and efficacious treatment for abdominal stereotactic body radiotherapy (SBRT). Expiratory breath hold (EBH) treatment is attractive as it does not require sophisticated gating technologies and minimizes abdominal target motion compared to inspiratory breath hold and abdominal compression; however, few patients can perform prolonged EBH to allow efficient treatment. We hypothesized that providing patients supplemental oxygen and controlling respiratory rate (RR) at the upper limit of normal would improve EBH times, increase the percentage of patients eligible for EBH treatment and decrease EBH treatment time. MATERIALS/METHODS: Starting in 2020, we provided patients supplemental oxygen (50% O2 via Venturi mask) with synchronization to a RR of 18 breaths/min with a metronome at the time of CT simulation. Patients were eligible for EBH treatment if they were able to complete two consecutive 20 second EBH. Eligible patients were treated per standard institutional guidelines for abdominal SBRT with EBH. We retrospectively identified all completed EBH treatments with this new supplemented procedure (EBHsupp) from our departmental database. Historical controls treated with EBH prior to this new procedure (EBHRA, where RA = room air) were identified and matched 1:1 based on patient age, sex, RT prescription, number of treatment arcs, and comorbidities via individual matching. Individual patient EBH times, total treatment time, cone beam CT (CBCT) time, and treatment arc time were extracted from the treatment planning software. Statistical comparisons were made with chi-squared test for categorical variables and student's t-test for continuous variables. RESULTS: We identified 8 patients that received 10 abdominal SBRT treatment plans with EBHsupp (two patients had two lesions requiring two separate treatment plans). There was no statistical difference between the EBHsupp and EBHRA groups with respect to patient characteristics. Eight of 11 (73%) screened EBHsupp patients were able to undergo EBH treatment compared to historical department standard of ∼30% with EBHRA. The EBHsupp group had a significant improvement in maximum (50.5 vs 30.9 s, P = 0.002) and median (24.0 vs 17.8 s, P = 0.016) EBH times compared to the EBHRA group and required less breath holds to complete their treatment (9.1 vs 13.9, P = 0.029). Time for CBCT was reduced with EBHsupp (6.5 vs 8.6 min, P = 0.004) and there was a trend towards decreased time for treatment arc completion (3.1 vs 4.0 min, P = 0,10) and overall treatment time (18.6 vs 21.7 min, P = 0.12). CONCLUSION: Providing supplemental oxygen and controlling respiratory rate at 18 breaths/min significantly improves EBH time. This intervention is simple, inexpensive, safe, and may allow more patients to be treated with EBH while decreasing overall treatment time. AUTHOR DISCLOSURE: C.S. Schneider: None. S. Shen: None. J.B.Fiveash: None. R. Jacob: None.