PURPOSE: The time structures of proton spot delivery in proton pencil beam scanning (PBS) radiation therapy are essential in many clinical applications. 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 ns, 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 recorded events and their 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 uncertainties were within 1.5% and are more precise than previously reported results. The measurements also revealed continuous sub-milliseconds proton spills at a low dose rate for the synchrotron accelerator and radiofrequency pulses at 7 µs and 1 ms repetition time for the synchrocyclotron accelerator. CONCLUSION: 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.

ADVACAM Prague Czech Republic

Department of Radiation Oncology and Winship Cancer Institute Emory University Atlanta Georgia USA

Department of Radiation Oncology Corewell Health Beaumont University Hospital Royal Oak Michigan USA

Department of Radiation Oncology Mayo Clinic Jacksonville Florida USA

Department of Radiation Oncology Mayo Clinic Phoenix Arizona USA

Department of Radiation Oncology Stanford University Palo Alto California USA

Zobrazit více v PubMed

Feng H, Shan J, Ashman JB, et al. Technical Note: 4D robust optimization in small spot intensity‐modulated proton therapy (IMPT) for distal esophageal carcinoma. Med Phys. 2021;48:4636‐4647. PubMed

Feng H, Sio TT, Rule WG, et al. Beam angle comparison for distal esophageal carcinoma patients treated with intensity‐modulated proton therapy. J Appl Clin Med Phys. 2020;21:141‐152. PubMed PMC

Liu C, Bhangoo RS, Sio TT, et al. Dosimetric comparison of distal esophageal carcinoma plans for patients treated with small‐spot intensity‐modulated proton versus volumetric‐modulated arc therapies. J Appl Clin Med Phys. 2019a;20:15‐27. PubMed PMC

Liu C, Schild SE, Chang JY, et al. Impact of spot size and spacing on the quality of robustly optimized intensity modulated proton therapy plans for lung cancer. Int J Radiat Oncol Biol Phys. 2018a;101:479‐489. PubMed PMC

Liu C, Sio TT, Deng W, et al. Small‐spot intensity‐modulated proton therapy and volumetric‐modulated arc therapies for patients with locally advanced non‐small‐cell lung cancer: a dosimetric comparative study. J Appl Clin Med Phys. 2018b;19:140‐148. PubMed PMC

Liu C, Yu NY, Shan J, et al. Technical note: treatment planning system (TPS) approximations matter—comparing intensity‐modulated proton therapy (IMPT) plan quality and robustness between a commercial and an in‐house developed TPS for nonsmall cell lung cancer (NSCLC). Med Phys. 2019b;46:4755‐4762. PubMed

Liu W, Liao Z, Schild SE, et al. Impact of respiratory motion on worst‐case scenario optimized intensity modulated proton therapy for lung cancers. Pract Radiat Oncol. 2015;5:e77‐e86. PubMed PMC

Liu W, Schild SE, Chang JY, et al. Exploratory study of 4D versus 3D robust optimization in intensity modulated proton therapy for lung cancer. Int J Radiat Oncol Biol Phys. 2016;95:523‐533. PubMed PMC

Shan J, Yang Y, Schild SE, et al. Intensity‐modulated proton therapy (IMPT) interplay effect evaluation of asymmetric breathing with simultaneous uncertainty considerations in patients with non‐small cell lung cancer. Med Phys. 2020;47:5428‐5440. PubMed PMC

Zou W, Zhang R, Schuler E, et al. Framework for quality assurance of ultrahigh dose rate clinical trials investigating FLASH effects and current technology gaps. Int J Radiat Oncol Biol Phys. 2023;116:1202‐1217. PubMed PMC

Liu G, Zhao L, Liu P, et al. The first investigation of spot‐scanning proton arc (SPArc) delivery time and accuracy with different delivery tolerance window settings. Phys Med Biol. 2023;68(21). doi:10.1088/1361-6560/acfec5 PubMed DOI

Deffet S, Hamaide V, Sterpin E. Definition of dose rate for FLASH pencil‐beam scanning proton therapy: a comparative study. Med Phys. 2023;50:5784‐5792. PubMed

Folkerts MM, Abel E, Busold S, Perez JR, Krishnamurthi V, Ling CC. A framework for defining FLASH dose rate for pencil beam scanning. Med Phys. 2020;47:6396‐6404. PubMed PMC

Harrison N, Kang M, Liu R, et al. A novel inverse algorithm to solve the integrated optimization of dose, dose rate, and linear energy transfer of proton FLASH therapy with sparse filters. Int J Radiat Oncol Biol Phys. 2024;119(3):957‐967. PubMed

Shen J, Tryggestad E, Younkin JE, et al. Technical note: using experimentally determined proton spot scanning timing parameters to accurately model beam delivery time. Med Phys. 2017;44:5081‐5088. PubMed

Zhao L, Liu G, Chen S, et al. Developing an accurate model of spot‐scanning treatment delivery time and sequence for a compact superconducting synchrocyclotron proton therapy system. Radiat Oncol. 2022a;17:87. PubMed PMC

Zhao L, Liu G, Zheng W, et al. Building a precise machine‐specific time structure of the spot and energy delivery model for a cyclotron‐based proton therapy system. Phys Med Biol. 2022;67(1). doi:10.1088/1361-6560/ac431c PubMed DOI

Younkin JE, Bues M, Sio TT, et al. Multiple energy extraction reduces beam delivery time for a synchrotron‐based proton spot‐scanning system. Adv Radiat Oncol. 2018;3:412‐420. PubMed PMC

Younkin JE, Morales DH, Shen J, et al. Technical note: multiple energy extraction techniques for synchrotron‐based proton delivery systems may exacerbate motion interplay effects in lung cancer treatments. Med Phys. 2021;48:4812‐4823. PubMed PMC

Liang X, Liu C, Furutani KM, et al. Investigation of beam delivery time for synchrotron‐based proton pencil beam scanning system with novel scanning mode. Phys Med Biol. 2022;67(17). doi:10.1088/1361-6560/ac8410 PubMed DOI

Charyyev S, Liu R, Yang X, et al. Measurement of the time structure of FLASH beams using prompt gamma rays and secondary neutrons as surrogates. Phys Med Biol. 2023;68(14). doi:10.1088/1361-6560/acdc7c PubMed DOI

Oancea C, Granja C, Marek L, et al. Out‐of‐field measurements and simulations of a proton pencil beam in a wide range of dose rates using a Timepix3 detector: dose rate, flux and LET. Phys Med. 2023a;106:102529. PubMed

Poikela T, Plosila J, Westerlund T, et al. Timepix3: a 65K channel hybrid pixel readout chip with simultaneous ToA/ToT and sparse readout. J Instrum. 2014;9. doi:10.1088/1748-0221/9/05/C05013 DOI

Oancea C, Solc J, Bourgouin A, et al. Thermal neutron detection and track recognition method in reference and out‐of‐field radiotherapy FLASH electron fields using Timepix3 detectors. Phys Med Biol. 2023;68(18). doi:10.1088/1361-6560/acf2e1 PubMed DOI

Turecek D, Jakubek J, Soukup P. USB 3.0 readout and time‐walk correction method for Timepix3 detector. J Instrum. 2016;11. doi:10.1088/1748-0221/11/12/C12065 DOI

Jakubek J. Precise energy calibration of pixel detector working in time‐over‐threshold mode. Nucl Instrum Meth A. 2011;633:S262‐S266.

Charyyev S, Chang CW, Harms J, et al. A novel proton counting detector and method for the validation of tissue and implant material maps for Monte Carlo dose calculation. Phys Med Biol. 2021;66:045003. PubMed

Granja C, Jakubek J, Soukup P, et al. MiniPIX Timepix3‐a miniaturized radiation camera with onboard data processing for online characterization of wide‐intensity mixed‐radiation fields. J Instrum. 2022a;17.

Granja C, Jakubek J, Soukup P, et al. Spectral tracking of energetic charged particles in wide field‐of‐view with miniaturized telescope MiniPIX Timepix3 1 x 2 stack. J Instrum. 2022b;17.

Novak A, Granja C, Sagatova A, Zach, Stursa J, Oancea C. Spectral tracking of proton beams by the Timepix3 detector with GaAs, CdTe and Si sensors. J Instrum. 2023;18.

Deng W, Younkin JE, Souris K, et al. Technical note: integrating an open source Monte Carlo code “MCsquare” for clinical use in intensity‐modulated proton therapy. Med Phys. 2020;47:2558‐2574. PubMed