Measuring the Time Structures of Proton Pencil Beam Scanning Delivery on a Microsecond Scale With Timepix3 Pixelated Semiconductor Detector

Document Type

Conference Proceeding

Publication Date

6-2024

Publication Title

International Journal of Particle Therapy

Abstract

Background and aims: The time structures of proton spot delivery in proton pencil beam scanning (PBS) radiation therapy are essential in many clinical applications, such as evaluating interplay effect, determining the dose rates in FLASH proton therapy, and optimizing proton plans using arc therapy. This study aims to characterize the time structures of proton PBS delivered by both synchrotron and synchrocyclotron accelerators using a non-invasive technique based on scattered particle tracking. Methods: A pixelated semiconductor detector, AdvaPIX-Timepix3, with a temporal resolution of 1.56 nanoseconds, was employed to measure time of arrival of secondary particles generated by a proton beam. The detector was placed laterally to the high-flux area of the beam in order to allow for single particle detection and not interfere with the treatment. The detector recorded counts of radiation events, their deposited energy and the timestamp associated with the single-events. Individual scattered particles and their spatial and temporal characteristics were used to analyze beam time structures, including energy layer switch time, magnet switch time, spot switch time, and the scanning speeds in the x and y directions. All the measurements were repeated 30 times on three dates, reducing statistical uncertainty. Results: The uncertainty of the measured energy layer switch times, magnet switch time, and the spot switch time were all within 1% of average values. The scanning speeds were within 1.5%. Key parameters measured with this detector are more precise than previously reported results (see Table 1). The measurements also revealed continuous sub-milliseconds proton spills at a low dose rate for the synchrotron accelerator and radiofrequency pulses at 7 microseconds and 1 milliseconds repetition time for the synchrocyclotron accelerator (see Figure 1). Conclusions: The AdvaPIX-Timepix3 detector can be used to directly measure and monitor time structures on microseconds scale of the PBS proton beam delivery. This method yielded results with high precision and is completely independent of the machine log files.

Volume

12

Issue

Suppl

First Page

50

Comments

62nd Annual Conference of the Particle Therapy Cooperative Group (PTCOG), June 10-15, 2024, Singapore

DOI

10.1016/j.ijpt.2024.100220

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