Purpose:A novel breathing guidance method by combining the personalized audio-visual biofeedback(BFB)system,the breath hold(BH)method,and the synchrotron-based gating technique was developed to help patients synchronize their respiratory patterns with the synchrotron pulsed manner to overcome typical limitations such as low efficiency and residual motion.In this work,four fractions were chosen to evaluate the reproducibility of subject compliance with the breathing guidance maneuvers among different fractions.Methods:A practical simulation was performed for a group of eight volunteers under passive scattering beam delivery mode with prescribed dose of 2 Gy.For each treatment fraction,the volunteers were directed to perform short BHs or short deep breath holds(SDBH)with the aid of BFB following a personalized standard BH/SDBH(stBH/stSDBH)guidance curve or his/her own representative BH/SDBH(reBH/reSDBH)guidance curve.Each session lasted for 10 min,and the breathing signal data were recorded in time sequence.The pre-selected threshold level for gating(duty cycle,DC)was set on each volunteer's breathing curves and the gating signal were superimposed onto the synchrotron magnet cycle excitation pattern to determine the total treatment time and mean absolute deviations(MAD)of the measured curves.Results:For the first treatment fraction,the decreases in the total treatment time by factors of 0.72-1.03 and 0.73-1.04 for the stBH/stSDBH and reBH/reSDBH guidance maneuvers were observed in contrast with conventional free breathing-based gated irradiation,depending on the DC settings.Moreover,the magnitude of residual motion using the respiratory guidance methods was almost 15 times less than during non-gated irradiation and good reproducibility among different fractions was achieved as shown in Figure 1 and Figure 2.Conclusions:The respiratory guidance methods not only improved the overall treatment efficiency of respiratory gating under passive scattering beam delivery mode,but also had the advantages of less residual motion and better reproducibility among fractions.Therefore,the novel breathing guidance technique might be very useful for respiratory motion management in synchrotron-based gated heavy-ion beam delivery.