A comprehensive characterization of the temporal characteristics of dose driven continuous scanning in proton therapy

Objective.To comprehensively characterize the temporal characteristics of dose-driven continuous scanning (DDCS) proton therapy system including the rise time to nominal beam current (trise), minimum time between break spot (tb), beam current fluctuation and the flap dose.Approach.Measurements were performed on a Hitachi proton therapy synchrotron. The beam current fluctuation was measured using a 20 kHz 2D strip ionization chamber (CROSSmini) with a fixed point irradiation without break points (BPs).trise,tband flap dose were quantified using an oscilloscope connected to the radiofrequency knockout (RFK), high-speed switching magnet (HSST), and dose monitor signals. These measurements were performed with BPs.trisewas measured and compared using both the analytical log file based and direct measurement approaches. The measurements were performed across three energies (70.2, 150.2 and 228.7 MeV), three beam currents (8, 14 and 20 MU s^-1) and five different spot MUs (6, 10, 20, 30 and 40 MU).Main results.The instantaneous beam current measured by CROSSmini showed fluctuations of up to 65%. After applying a 1.0 ms moving average, the beam current coincides with the log file recorded beam current, thereby validating the latter data. The time delay between RFK off and HSST on was (0.08 ± 0.01) ms and minimal flap dose was recorded with an average of 4μMU. The minimum time between break spots was measured to be (1.67 ± 0.04) ms. The analytical log file-based and direct measurement oftrisewere correlated with a Pearson correlation coefficient of 0.86. Thetrisemeasurement across the entire spills showed a dependence on beam current where 8 MU s^-1had a notably highertrisethan 14 and 20 MU s^-1.Significance.This is the first comprehensive study to characterize the temporal properties of a DDCS proton therapy system. The methodology introduced in this work would help in the proton DDCS commissioning efforts in other centers.