M Delafuente*, S Oliaei Motlagh, M Kim, S Feigenberg, L Dong, E Diffenderfer, University of Pennsylvania, Philadelphia, PA

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  M Delafuente

WE-C1000-IePD-F3-4 (Wednesday, 7/13/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: To quantify the delay in beam on/off response and corresponding dose discrepancy in the Universal Beam Triggering Interface (UBTI) of the IBA Proteus Plus Proton Therapy System.

Methods: A beam triggering signal configured to 0.5 s on-time and 2 s off-time was supplied to the UBTI to gate the delivery of a proton PBS plan. Integral dose was measured by an ionization chamber in solid water and electrometer. A multi-channel fast-sampling electrometer simultaneously recorded the beam triggering signal and beam current measured with a Faraday cup placed behind the ionization chamber. Time delay for beam on and beam off states were measured by examining the overlaying beam triggering and current signals. Charge delivered during the beam off delay was calculated by integrating the residual Faraday cup current.

Results: The time delay for beam-on activation was found to be 149.7 ± 19.9 ms. For beam-off cycles that occur between PBS spots, there is no beam-off delay. For those cycles that ended during spot delivery, delay for beam deactivation was 10 ± 0.3 ms. Charge delivered during the beam-off delay was on average 0.137 nC or 2.56% of the total field charge. The uniform field dose was 0.81 Gy with an average dose rate of 0.18 Gy/s, resulting in an average 2.75 mGy residual dose delivered during the beam-off latency.

Conclusion: At conventional dose rates, the residual dose error due to beam-off latency of the proton beam triggering interface is negligible. However, at ultra-high dose rates for FLASH proton therapy with dose rates >40Gy/s, the use of the UBTI may introduce a significant beam-off dose error for applications sensitive to beam triggering accuracy.

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