ArticleJournal of applied clinical medical physics2026
End-to-end film-based characterization of gated delivery latencies in a spot-scanned synchrotron-based proton therapy system.
Article in Journal of applied clinical medical physics, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundTemporal 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.
methodsGating 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.
resultsAn average beam-on latency of
conclusionA 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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