End-to-end film-based characterization of gated delivery latencies in a spot-scanned synchrotron-based proton therapy system.
- 1Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota, USA.
Abstract
Background
Temporal mismatches between gating signals and beam activation-beam-on and beam-off latencies-in gated particle beam therapy can compromise dose integrity. Yet standardized measurement techniques are lacking, and system-specific characterization, particularly for synchrotron-based proton systems, remains limited.Purpose
To implement a novel strategy for precise end-to-end gating latency measurements of a spot-scanned proton beam using Gafchromic film.Methods
Gating latencies have been measured for a Hitachi ProBeat accelerator equipped with a Varian RPM gating system. EBT4 films were positioned within a stack of acrylic blocks on a QUASAR respiratory motion platform operated with a 1.5 cm amplitude and 12 bpm sinusoidal pattern. A stainless-steel ball bearing (BB), positioned atop the film, facilitated localization. During irradiation, the BB produced a dose shadow on the film that indicated the phantom position. A proton plan consisting of a single 85.3 MeV spot was delivered to isocenter during a single gate-on/off interval initiated near the 25% phase, to maximize phantom velocity. Fifty-one measurements were made with a variety of gating intervals. Beam-on latency and delivery time produced a separation between the BB-shadow and the centroid of the Gaussian proton spot. Spot duration information was extracted from accelerator log files. BB-shadow/spot separation is modeled analytically based on phantom motion enabling the direct calculation of the total beam-on and beam-off latencies. Accelerator latency was measured directly with an oscilloscope, enabling isolation of the relative contributions of the RPM gating system.Results
An average beam-on latency of 142±27 ms is observed for the RPM+ProBeat system for the first gate of a delivery, which includes a known 69 ms beam extraction judgment time for the first proton spot in a spill from the Hitachi synchrotron. The corresponding average beam-off latency is 87±30ms . The average gate-on and gate-off latencies of the RPM system are calculated as 72±27ms and 81±30ms , respectively. The associated average contributions of the accelerator to the beam-on latencies are measured as 69.3±0.2ms (first gate in new spill) and 0.53±0.07ms (subsequent gates in existing spill) and similarly 6±4ms for beam-off latency.Conclusion
A novel, high-precision method for gating-latency measurements has been implemented using film to characterize gating latencies in a spot-scanned particle beam. Commissioning and regular quality assurance methods to precisely characterize the temporal accuracy of a gating system ensure treatment accuracy and will become increasingly vital to consider for higher-frequency applications, such as cardiac gating or FLASH-capable systems.
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BibTeX
@article{stottler2026endtoend,
title = {{End-to-end film-based characterization of gated delivery latencies in a spot-scanned synchrotron-based proton therapy system.}},
author = {Z S Stottler and J J Kruse and A J Deisher},
journal = {Journal of applied clinical medical physics},
year = {2026},
month = oct,
doi = {10.1002/acm2.70826},
url = {https://europepmc.org/article/MED/42905951},
note = {CC BY},
}
RIS
TY - JOUR
TI - End-to-end film-based characterization of gated delivery latencies in a spot-scanned synchrotron-based proton therapy system.
AU - Z S Stottler
AU - J J Kruse
AU - A J Deisher
PY - 2026
DA - 2026/10/30
JO - Journal of applied clinical medical physics
DO - 10.1002/acm2.70826
UR - https://europepmc.org/article/MED/42905951
AB - Background Temporal mismatches between gating signals and beam activation-beam-on and beam-off latencies-in gated particle beam therapy can compromise dose integrity. Yet standardized measurement techniques are lacking, and system-specific characterization, particularly for synchrotron-based proton systems, remains limited.Purpose To implement a novel strategy for precise end-to-end gating latency measurements of a spot-scanned proton beam using Gafchromic film.Methods Gating latencies have been measured for a Hitachi ProBeat accelerator equipped with a Varian RPM gating system. EBT4 films were positioned within a stack of acrylic blocks on a QUASAR respiratory motion platform operated with a 1.5 cm amplitude and 12 bpm sinusoidal pattern. A stainless-steel ball bearing (BB), positioned atop the film, facilitated localization. During irradiation, the BB produced a dose shadow on the film that indicated the phantom position. A proton plan consisting of a single 85.3 MeV spot was delivered to isocenter during a single gate-on/off interval initiated near the 25% phase, to maximize phantom velocity. Fifty-one measurements were made with a variety of gating intervals. Beam-on latency and delivery time produced a separation between the BB-shadow and the centroid of the Gaussian proton spot. Spot duration information was extracted from accelerator log files. BB-shadow/spot separation is modeled analytically based on phantom motion enabling the direct calculation of the total beam-on and beam-off latencies. Accelerator latency was measured directly with an oscilloscope, enabling isolation of the relative contributions of the RPM gating system.Results An average beam-on latency of 142±27 ms is observed for the RPM+ProBeat system for the first gate of a delivery, which includes a known 69 ms beam extraction judgment time for the first proton spot in a spill from the Hitachi synchrotron. The corresponding average beam-off latency is 87±30ms . The average gate-on and gate-off latencies of the RPM system are calculated as 72±27ms and 81±30ms , respectively. The associated average contributions of the accelerator to the beam-on latencies are measured as 69.3±0.2ms (first gate in new spill) and 0.53±0.07ms (subsequent gates in existing spill) and similarly 6±4ms for beam-off latency.Conclusion A novel, high-precision method for gating-latency measurements has been implemented using film to characterize gating latencies in a spot-scanned particle beam. Commissioning and regular quality assurance methods to precisely characterize the temporal accuracy of a gating system ensure treatment accuracy and will become increasingly vital to consider for higher-frequency applications, such as cardiac gating or FLASH-capable systems.
SN - 1526-9914
ER -