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Publications (33)
Matthias Würl, Grigory Liubchenko, Guyue Hu, Katrin Schnürle, Sebastian Meyer, Jonathan Bortfeldt, Guillaume Landry, Lukas Käsmann, Kirsten Lauber, Carlos Granja, Cristina Oancea, Enrico Verroi, Francesco Tommassino, Katia Parodi
Orthotopic tumor models in pre-clinical translational research require accurate tumor localization for effective irradiation, which is challenging due to limited tissue contrast in x-ray and proton computed tomography (xCT and pCT). This study investigates gadolinium oxide nanoparticles as a multimodal contrast agent for these imaging modalities. Proton radiographies were conducted using MiniPIX-Timepix detectors with gadolinium oxide dispersions. Simulations of pCT imaging were performed using a Monte Carlo framework with varied nanoparticle concentrations. CBCT imaging was also evaluated using a PMMA phantom. The study found significant contrast enhancement in proton radiography at 4wt% and detectability in pCT at similar levels, while xCT achieved detectability at just 0.5wt%. The findings highlight the feasibility of gadolinium oxide for enhancing proton imaging contrast, although achieving sufficient in-vivo concentrations poses a challenge. Targeting or injection strategies could address this limitation, and advanced pCT techniques like scattering pCT and PIXE may further improve tumor localization.
Cristina Oancea, Katerina Sykorova, Jan Jakubek, Jiri Pivec, Felix Riemer, Steven Worm, Alexandra Bourgouin
Background: FLASH radiotherapy necessitates the development of advanced Quality Assurance methods and detectors for accurate monitoring of the radiation field. This study introduces enhanced time-resolution detection systems and methods used to measure the delivered number of pulses, investigate temporal structure of individual pulses and dose-per-pulse (DPP) based on secondary radiation particles produced in the experimental room. Methods: A 20 MeV electron beam generated from a linear accelerator (LINAC) was delivered to a water phantom. Ultra-high dose-per-pulse electron beams were used with a dose-per-pulse ranging from ~1 Gy to over 7 Gy. The pulse lengths ranged from 1.18 µs to 2.88 µs at a pulse rate frequency of 5 Hz. A semiconductor pixel detector Timepix3 was used to track single secondary particles. Measurements were performed in the air, while the detector was positioned out-of-field at a lateral distance of 200 cm parallel with the LINAC exit window. The dose deposited was measured along with the pulse length and the nanostructure of the pulse. Results: The time of arrival (ToA) of single particles was measured with a resolution of 1.56 ns, while the deposited energy was measured with a resolution of several keV based on the Time over Threshold (ToT) value. The pulse count measured by the Timepix3 detector corresponded with the delivered values, which were measured using an in-flange integrating current transformer (ICT). A linear response (R² = 0.999) was established between the delivered beam current and the measured dose at the detector position (orders of nGy). The difference between the average measured and delivered pulse length was ~0.003(30) μs. Conclusion: This simple non-invasive method exhibits no limitations on the delivered DPP within the range used during this investigation.
Jacinta S.L. Yap, Navrit J.S. Bal, Mark D. Brooke, Cristina Oancea, Carlos Granja, Andrzej Kacperek, Simon Jolly, Frank Van den Heuvel, Jason L. Parsons, Carsten P. Welsch
Proton therapy can achieve a highly targeted treatment by utilising the advantageous dosimetric characteristics of the Bragg Peak. Protons traversing through a material will deposit their maximum energy at the Bragg Peak through ionisation and other interactions, transferring minimal excess dose to surrounding tissue and organs. This rate of energy loss is also quantified by the linear energy transfer (LET), which is indicative of radiation quality and radiobiological effects. However it is a challenging physical quantity to measure, as characterisation of radiation fields and the impact of LET on treatment requires advanced tools and technology. The MiniPIX-Timepix is a miniaturised, hybrid semiconductor pixel detector capable of high resolution spectrometric tracking, enabling wide-range detection of the deposited energy, position and direction of single particles. Experimental measurements were performed at a clinical facility, the Clatterbridge Cancer Centre which houses a 60 MeV ocular proton therapy beamline. A realistic end-to-end model of the facility was developed in the Monte Carlo code TOPAS (TOol for PArticle Simulation) and was used to simulate the experimental conditions. The detector was held at 45° and 60° perpendicular to the beam, and placed downstream of various thickness Polymethyl methacrylate (PMMA) blocks to acquire data along the dose deposition depth. Empirical cluster data providing track length and the energy deposition distributions were used to obtain the LET spectra. The determined values for the LET in silicon and dose averaged LET across the BP show general agreement with simulated results, supporting the applicability of the TOPAS CCC model. This work explores the capability of the MiniPIX detector to measure physical quantities to resolve the LET, and discusses experimental considerations and further possibilities.
Carlos Granja, Samuel Kurucz, Jaroslav Solc, Vladimir Vondracek, Josef Pacik, Cristina Oancea
In particle radiotherapy practice it is valuable to examine, accurately measure and monitor the secondary radiation fields produced during treatment. Measurements performed non-invasively and out-of-field avoid interfering with and modifying the delivered dose treatment. Use of a simplified and compact device is advantageous for reduced cost and effort of deployment and operation. For this purpose, we examine in detail the scattered beam particles and secondary radiation field produced well beyond even meters away from the irradiated area in proton therapy. We use the semiconductor pixel detector Timepix3 implemented as a miniaturized radiation camera which we mounted at the ceiling of the treatment room. The pixel detector provides high-resolution per-pixel spectrometry with time, position, directional and tracking response. Applying radiation imaging and particle tracking techniques together with extensive experimental calibrations in well-defined radiation fields, the single detector provides the composition and spectral-tracking characterization of the complex fields. In particular, the scattered proton field at the detector position is evaluated and unfolded into spectral-directional groups which serve to map and examine the characteristics and directional origin of the radiation out of field. Detailed particle fluxes and dose rates, total and partial, are measured out of field with sub-second time resolution. Deposited energy distributions in the detector sensor are derived in wide range. Verification and complementary information are provided by numerical Monte-Carlo (MC) simulations. The combined results and presented technique can be potentially used to inspect and systematically evaluate quality assurance irradiations and treatment plans.
Paulina Stasica-Dudek, Carlos Granja, Renata Kopeć, Dawid Krzempek, Cristina Oancea, Antoni Rucinski, Marzena Rydygier, Mateusz Winiarz, Jan Gajewski
Objective. This study addresses the need for experimental validation of linear energy transfer (LET) in proton therapy by presenting a methodology and results for LET spectra measurements using a miniaturized Timepix3 pixel detector. Approach. LET was measured in spread-out Bragg peak (SOBP) and IMPT fields using homogeneous and heterogeneous phantoms. A GPU-accelerated Monte Carlo (MC) simulation was used for validation. Main results. Experimental results showed good agreement with MC simulations, with a mean relative difference in dose-averaged LET of ~5.1%. Significance. This validates the feasibility of using the Timepix3 detector for LET-based patient-specific quality assurance (PSQA) in proton therapy, supporting future clinical implementation of LET optimization in treatment planning.
Linh Tran, Cristina Oancea, Satoshi Kodaira, David Bolst, James Vohradsky, Carlos Granja, Jan Jakubek, Jaroslav Šolc, Elisabeth Bodenstein, Sebastian Gantz, Jörg Pawelke, Lukas Marek, Anatoly Rosenfeld
Fragments and neutrons produced by inelastic reactions in particle therapy can make a significant contribution to the Relative Biological Effectiveness (RBE) and as a consequence the biologically weighted-dose in the distal part of the Spread-out Bragg Peak (SOBP); this also make changes to the radiation quality and dose equivalent in surrounding organs near the target tumour. These mixed radiation fields of secondary fragments and neutrons are difficult to characterise which is why this paper reviews some solid state radiation detectors that can measure the radiation field produced out of primary field in particle therapy, and also assess the radiation quality and dose equivalent to normal organs located near the target volume. These detectors include active types such as the silicon on insulator (SOI) microdosimeter, the monolithic ΔE-E telescope, the pixel detectors TimePix3, and passive detectors such as CR-39 plastic charged particle track detector, and the fluorescent nuclear track detector (FNTD). This paper also reports on the microdosimetric measurements obtained with silicon-based microdosimeters, both laterally and downstream of the target volume, for proton and carbon ion beams. It also details the measurements taken by the TimePix3 detector, including a customised, miniaturized version with enhanced resolving power, for characterizing secondary radiation in proton therapy through single-particle tracking. The CR-39 and FNTD passive linear energy transfer (LET) detectors are also reviewed and the advantages and disadvantages of each type of detector are discussed. The SOI microdosimeter and ΔE-E telescope are suitable for characterising the typical mixed radiation field for out-of-field in particle therapy. An SOI microdosimeter can provide dose equivalent values to evaluate risk to normal organs, while the ΔE-E telescope can operate as a microdosimeter and distinguish the type of particles in the secondary radiation field. The TimePix3 chip can provide mixed field decomposition, particle flux, dose rate, and LET spectra while the CR-39 plastic detector could measure the LET spectra, absorbed dose, and dose equivalent from secondary particles of Carbon ion beam via nuclear targeted fragmentation reactions.
Paulina Stasica-Dudek, Cristina Oancea, Carlos Granja, Konrad Guguła, Jan Jakubek, Renata Kopeć, Dawid Krzempek, Michal Matous, Antoni Rucinski, Marzena Rydygier, Jan Gajewski
Purpose: With the increasing use of proton therapy, there is a growing emphasis on including radiation quality, often quantified by linear energy transfer, as a treatment plan optimization factor. The Timepix detectors offer energy-sensitive particle tracking useful for the characterization of proton linear energy transfer. To improve the detector's performance in mixed radiation fields produced in proton therapy, we customized the detector settings and performed the per-pixel energy calibration. Methods: The detection threshold and per-pixel signal shaping time (I krum current) were customized, and energy calibration was performed for MiniPIX Timepix3. The detector calibration was verified using α source and clinical proton beams, as well as Monte Carlo simulations. The effects on the detector's performance, in terms of spectral saturation and pixel occupancy, were evaluated. Results: Measurements with proton beams showed a good agreement with simulations. With the customized settings, the measurable energy range in the detector data-driven mode was extended, and the signal duration time was reduced by 80%, while the yield of pixel time occupancy reduction depends on the number of occupied pixels. For performed measurements with proton beams, the number of occupied pixels was further reduced up to 40% due to the increased threshold. Conclusions: Customized detector configuration of the Timepix3 detector allowed for reduced pixel occupancy and mitigation of signal saturation in a data-driven mode without significantly interfering with the energy deposition measurement. The presented approach enables the extension of the operational range, including higher intensities and mixed-radiation fields in particle radiotherapy environments.
C. Oancea, J. Šolc, C. Granja, E. Bodenstein, F. Horst, J. Pawelke, J. Jakubek
This study investigates the response of Timepix3 semiconductor pixel detectors in proton beams of varying intensities, with a focus on FLASH proton therapy. Using the Timepix3 application-specific integrated circuit (ASIC) chip, we measured the spatial and spectral characteristics of 220 MeV proton beams delivered in short pulses. The setup involved Minipix readout electronics integrated with a Timepix3 chipboard and Advapix Timepix3 with a silicon sensor. The bare Timepix3 ASIC chip was also evaluated. Results showed the capability of Timepix3 detectors to measure ToT and event counts in both conventional and UHDR proton beams. The bare ASIC sustained up to 270 Gy/s dose rates.
K. Sykorova, Z. Buk, M. Cepek, C. Granja, C. Oancea, L. Marek
Semiconductor hybrid pixel detectors with Timepix 3 ASIC chips developed by the Medipix collaboration at CERN enable high-resolution, single-particle detection, measuring deposited energy and time of arrival per pixel. This study introduces machine learning models—BiLSTM, fully connected neural networks, and CatBoost decision trees—for classifying individual particle events based on morphological and spectral features. These models were trained on an extensive, labeled experimental dataset and validated on a separate test set. Classification was performed across five particle categories: electrons & photons, alpha particles, heavy nuclei, low-energy protons, and high-energy protons. The models demonstrated high accuracy, with BiLSTM requiring no preprocessing but slower inference, while CatBoost achieved the fastest predictions. Additionally, an unsupervised Gaussian Mixture Model was used to explore the separation between electrons and photons. Feature importance analysis revealed LET, energy distribution, and cluster morphology as key discriminators. Future work will integrate these models into the TraX Engine platform developed by ADVACAM.
C. Bălan, C. Granja, G. Mytsin, S. Shvidky, A. Molokanov, V. Chiș, C. Oancea
A rapid increase in the use of proton therapy for cancer treatment has been seen in the last decade due to its clinical advantages. Therefore, more and more patients with implants and other metallic devices will be among those who will be treated. This study experimentally examines the effect and changes in the delivered fields, using water-equivalent phantoms with and without titanium (Ti) dental implants positioned along the primary beam path. We measured in detail the composition and spectral-tracking characterization of particles generated in the plateau region of the Bragg curve towards the Sub-peak region using high-spatial resolution, spectral and time-sensitive imaging detectors with a pixelated array provided by the ASIC chip Timepix3. A 170 MeV proton beam was collimated and modulated in a polymethyl methacrylate (PMMA) block. Placing two dental implants behind the PMMA block, the radiation was measured using two pixeled detectors with silicon (Si) sensors. The Timepix3 (TPX3) detectors measured in detail particle fluxes, dose rates (DR) and linear energy transfer (LET) spectra for resolved particle types. Artificial intelligence (AI)-based trained neural networks (NN) calibrated in well-defined radiation fields were used to analyze and identify particles based on morphology and characteristic spectral-tracking response. The beam was characterized and single-particle tracks were registered and decomposed into particle-type groups. The resulting particle fluxes in both setups are resolved into three main classes of particles: i) protons, ii) electrons and photons, and iii) ions. Protons are the main particle component responsible for dose deposition. High-energy transfer particles (HETP), namely ions, exhibited differences in both dosimetric aspects that were investigated: DR and particle fluxes, when the Ti implants were placed in the setup. The detailed multi-parametric information of the secondary radiation field provides a comprehensive understanding of the impact of Ti materials in proton therapy.
L. Marek, C. Granja, J. Jakubek, J. Ingerle, D. Turecek, M. Vuolo, C. Oancea
Hybrid semiconductor pixelated detectors from the Timepix family are advanced detectors for online particle tracking, offering energy measurement and precise time stamping capabilities for particles of various types and energies. This inherent capability makes them highly suitable for various applications, including imaging, medical fields such as radiotherapy and particle therapy, space-based applications aboard satellites and the International Space Station, and industrial applications. The data generated by these detectors is complex, necessitating the development and deployment of various analytical techniques to extract essential information. For this purpose, and to aid the Timepix user community, the "Data Processing Engine" (DPE) was developed as an advanced tool for data processing designed explicitly for Timepix detectors. The DPE includes three processing levels: pre-processing (clusterization, calibrations, corrections), processing (particle classification using machine learning, radiation field recognition), and post-processing (directional and coincidence analysis, physics products generation). It is supported by a database of typical radiation field references and is accessible via command-line, API, and web interface.
Carlos Granja, Corinne Barber, Sandra Barna, Jeffery Chancellor, David Chvatil, Loic Grevillot, David Inzalaco, Jan Jakubek, Zdenek Kohout, Giulio Magrin, Lukas Marek, Radu Mihai, Cristina Oancea, Vaclav Olsansky, Trevor Olsen, Dusan Poklop, Stanislav Pospisil, Andreas Resch, Andrea Sagatova, Michael Sivertz, Jan Stursa, Rudolf Sykora, Ivan Wilhelm, Vaclav Zach, Bohumir Zatko
Silicon Carbide is a suitable semiconductor sensor for radiation measurement and nuclear applications. It has been recently implemented as a position-sensitive and radiation imaging device coupled to the Timepix3 ASIC chip in the form of a miniaturized radiation camera MiniPIX-Timepix3 SiC. In this work we systematically evaluate the detection resolving power to different radiation species: electrons, fast neutrons, ions and protons. Experimental calibrations were made at well-defined reference fields in terms of particle type, energy and direction. The spectral-sensitive tracking response and characteristic morphology of the particle tracks are analyzed by pattern recognition algorithms. The low thickness of the radiation sensitive volume (65 μm) of the SiC sensor limits the directional tracking response and angular resolution. Three broad classes of particle-type events are resolved. The detector together with suitable data processing can be used for radiation dosimetry and particle tracking tasks in space, particle therapy, nuclear physics and nuclear reactors and particle accelerator environments.
C. Granja, R. Uhlar, D. Poklop, P. Alexa, V. Zach, C. Oancea, L. Marek
Monitoring and characterization of particle beams in wide-range is often necessary in research and many applications with particle accelerators. The quantitative measurement and evaluation of composition especially of high-intensity beams are limited and can become a challenge with conventional methods especially with simplified instrumentation for ease of deployment. For this purpose, we developed a novel technique based on high-resolution spectral-sensitive tracking of single particles scattered from the beam path by a thin foil. We use a compact radiation camera equipped with the semiconductor pixel detector Timepix3 together with dedicated Monte-Carlo simulations. Particle-event type discrimination and directional information are produced by the detector spectral-tracking response together with particle-type resolving power derived from experimental calibrations. Directional- and spectral-sensitive components can be resolved in wide field-of-view. Quantification of the primary beam intensity is extrapolated by numerical calculations. Demonstration and evaluation of the technique are provided by measurements with 33 MeV protons from a light ion cyclotron accelerator. Scattered particles originating from the thin foil, the accelerator beam nozzle, and the air space along the beam path are detected and evaluated.
C. Granja, J. Solc, J. Gajewski, A. Rucinski, P. Stasica, M. Rydygier, L. Marek, C. Oancea
Mixed radiation fields in environments such as particle radiotherapy and outer space exhibit large complexity in terms of composition and spectral distribution which are difficult to measure in detail. For this purpose, we present a high-sensitivity technique using the pixel detector Timepix3 to measure the composition and spectral-tracking characterization of secondary fields produced in proton radiotherapy. Particle-event classes are resolved into broad groups of high-energy transfer particles (HETP), such as protons, ions and neutrons, as well as low-energy transfer particles (LETP), such as electrons, X rays and, partly, low-energy gamma rays. The quantum-imaging capability of Timepix3 is exploited to enhance the resolving power for particle-type classification. The particle tracks are analyzed by spectral-sensitive pattern recognition algorithms. The response matrix for Timepix3 is newly derived based on experimental calibrations in well‑defined radiation fields including in‑beam rotational scans of protons performed at various energies and directions. Clinical proton beams of radiotherapeutic intensities and energies in the range 12–225 MeV were used in experimental configurations with and without a tissue‑equivalent phantom. Detailed results of radiation components can be used to produce total and partial particle fluxes, dose rate, absorbed dose, deposited energy and linear‑energy‑transfer (LET) spectra. Dedicated Monte Carlo (MC) simulations are compared with experimental results of field composition, particle fluence, and deposited energy. The numerical information aids the interpretation of experimental data which includes also secondary neutrons. The technique and developed methodology can be applied for research and routine measurements in environments of varying complexity.
C. Oancea, A. Resch, S. Barna, G. Magrin, L. Grevillot, D. Hladik, L. Marek, J. Jakubek, C. Granja
This study evaluates the operational limits of Timepix2 and Timepix3 pixel detectors under high particle flux conditions using alpha particles, protons, and carbon ions. It demonstrates that Timepix2, with customized calibration (Ikrum = 30, THL = 10 keV), enables single-particle tracking at fluxes up to 10⁹ particles/cm²/s with acquisition times as short as 100 ns, preserving spectral accuracy. This contrasts with Timepix3, which loses charge information below 100 µs. The results support Timepix2’s applicability in clinical beam environments for proton and carbon ion radiotherapy without reducing beam current.
Jiajian Shen, Xuanfeng Ding, Serdar Charyyev, Xiaoying Liang, Cristina Oancea, Peilong Wang, William G. Rule, Wei Liu, Martin Bues, Liyong Lin
The time structures of proton spot delivery in pencil beam scanning (PBS) proton therapy are critical for applications like 4D dose calculations and FLASH therapy. This study uses a pixelated semiconductor detector, AdvaPIX-Timepix3, with a temporal resolution of 1.56 ns, to directly measure proton delivery time structures for synchrotron and synchrocyclotron accelerators. Measurements captured key parameters such as energy layer switch time, magnet switch time, and spot switch time, with uncertainties below 1.5%. Results revealed near-continuous proton spill for synchrotron systems and high-intensity pulsed delivery for synchrocyclotrons. The findings demonstrate that the AdvaPIX-Timepix3 detector provides a precise, non-invasive alternative to log-file based methods for characterizing time structures of therapeutic proton beams.
Carlos Granja, Herve Chanal, Vaclav Zach, David Chvatil, Cristina Oancea, Dusan Poklop, Vaclav Olsansky, Jan Jakubek
We performed detailed measurements of the secondary cosmic ray field in the lower atmosphere using a miniaturized particle telescope composed of two closely stacked Timepix3 detectors in synchronized operation. This configuration allows position-, spectral-, and time-sensitive particle tracking, enabling high angular resolution and enhanced particle-type discrimination. Validation was performed with proton and electron beams. Ground-based cosmic ray measurements at 200 m altitude (Prague) yielded detailed composition and directional distributions of the charged particle component, notably muons. The angular flux of muons was measured across a wide field-of-view with enhanced discrimination from photon and electron components. Experimental results are compared with model estimates, demonstrating the telescope's capability for precise cosmic radiation mapping with compact instrumentation.
Cristina Bălan, Carlos Granja, Gennady Mytsin, Sergey Shvidky, Alexander Molokanov, Lukas Marek, Vasile Chiș, Cristina Oancea
This study evaluates the composition of scattered particles in proton therapy near titanium dental implants. Using a therapeutic conformal proton beam, the experiment was conducted on a head phantom implanted with Ti and plastic inserts. A MiniPIX Timepix3 hybrid pixel detector was used to detect scattered radiation behind the tumor during irradiation. Algorithms trained with artificial intelligence (AI) were used to recognize particles and decompose the radiation field. Measurements were collected at two beam angles (0° and 60°), and AI identified protons, electrons & photons, and fast neutrons. Scattered radiation with Ti implants was mainly electrons and photons (52.2%), while plastic implants showed higher proton contributions (65.4%). LET spectra ranged from 0.01 to 7.5 keV/μm. Low-LET was mostly from electrons and photons, and high-LET from protons and ions. The findings help quantify out-of-field radiation risks, supporting safer, more precise treatment validation.
Nathan Harrison, Serdar Charyyev, Cristina Oancea, Alexander Stanforth, Edgar Gelover, Shuang Zhou, William S Dynan, Tiezhi Zhang, Steven Biegalski, Liyong Lin
This study presents a methodology to validate dose, dose rate (DR), and linear energy transfer (LET) in ultra high dose rate (UHDR) proton therapy, also known as conformal FLASH. FLASH aims to reduce normal tissue damage while preserving tumor control, but its clinical use is limited by challenges in quality assurance (QA) measurements. Researchers used a 250-MeV proton beam and a 3D-printed ridge filter to deliver conformal FLASH to a spherical target. Dose and DR were measured using a 4D multi-layer strip ionization chamber (MLSIC), while LET was assessed using a high-resolution Timepix3 detector with an under-sample and recover (USRe) technique to avoid pile-up. Results from these measurements were compared with those from the MatriXX PT detector and Monte Carlo simulations. The data showed high agreement between experimental results and simulations, with >95% gamma passing rates for dose comparisons and <0.3% difference in DR at the lateral margins. LET measurements also showed strong alignment, with Bhattacharyya distances <1.3% across margins. The study concludes that this methodology is effective for experimental validation and QA of FLASH treatment plans.
Paulina Stasica, Hanh Nguyen, Carlos Granja, Renata Kopeć, Lukas Marek, Cristina Oancea, Łukasz Raczyński, Antoni Rucinski, Marzena Rydygier, Keith Schubert, Reinhard Schulte, Jan Gajewski
Protons have advantageous dose distributions and are increasingly used in cancer therapy. At the depth of the Bragg peak range, protons produce a mixed radiation field with low- and high-linear energy transfer (LET) components, where the high-LET is associated with increased biological effectiveness. LET prediction by Monte Carlo simulations is challenging to verify experimentally. This study presents measurements using the Timepix detector in a mixed radiation field produced by a therapeutic proton beam in water, validated by Monte Carlo simulations. The Timepix detector, with high-resolution particle tracking enhanced by artificial intelligence, identified particle types and measured deposited energy. Biologically relevant LET parameters, including single proton LET and dose-averaged LET, were computed. The neural network achieved over 95% accuracy in proton recognition. The LET spectra from measurements matched simulations with a mean dose-averaged LET difference of 17%. A wide LET range from sub-keV/μm to 10 keV/μm was observed. The proposed method offers accessible, experimental LET data for treatment planning validation and can be implemented in clinical proton therapy facilities.
Cristina Oancea, Jaroslav Solc, Alexandra Bourgouin, Carlos Granja, Jan Jakubek, Jiri Pivec, Felix Riemer, Zdenek Vykydal, Steven Worm, Lukas Marek
This study investigates the generation and detection of thermal neutrons in FLASH (ultra-high dose rate) electron beams. Approach. Measurements were conducted at a clinical linac using a Timepix3 pixel detector with a ⁶LiF neutron converter. Data were collected under different configurations and analyzed to characterize neutron interactions. Main results. Thermal neutron fluences of up to ~10⁶ cm⁻² Gy⁻¹ were observed, with clear spatial patterns and good agreement with Monte Carlo simulations. Significance. This is the first experimental observation and quantification of thermal neutrons in FLASH electron beams, highlighting a need to consider their presence in dosimetric assessments and biological effect studies.
A. Novak, C. Granja, A. Sagatova, J. Jakubek, B. Zatko, V. Vondracek, M. Andrlik, V. Zach, S. Polansky, A. Rathi, C. Oancea
The hybrid architecture of the Timepix (TPX) family of detectors enables the use of different semiconductor sensors, most commonly silicon (Si), as well as high-density materials such as Cadmium Telluride (CdTe) or Gallium Arsenide (GaAs). For this purpose, we explore the potential of a silicon carbide (SiC) sensor bump-bonded on a Timepix3 detector as a radiation imaging and particle tracking detector. SiC stands as a radiation-hard material also with the ability to operate at elevated temperatures up to several hundreds of degrees Celsius. As a result, this sensor material is more suitable for radiation harsh environments compared to conventional Si sensors. In this work, we evaluate the response for precise radiation spectrometry and high-resolution particle tracking of newly developed SiC Timepix3 detector which is built and operated as a compact radiation camera MiniPIX-Timepix3 with integrated readout electronics. Calibration measurements were conducted with mono-energetic proton beams with energies of 13, 22, and 31 MeV at the U-120M cyclotron at the Nuclear Physics Institute Czech Academy of Science (NPI CAS), Prague, as well as 100 and 226 MeV at the Proton Therapy Center Czech (PTC) in Prague. High-resolution pattern recognition analysis and single-particle spectral tracking are used for detailed inspection and understanding of the sensor response. Results include distributions of deposited energy and linear energy transfer (LET) spectra. The spatial uniformity of the pixelated detector response is examined in terms of homogeneously distributed deposited energy.
Cristina Oancea, Carlos Granja, Lukas Marek, Jan Jakubek, Jaroslav Šolc, Elisabeth Bodenstein, Sebastian Gantz, Jörg Pawelke, Jiri Pivec
Stray radiation produced by ultra-high dose-rates (UHDR) proton pencil beams is characterized using ASIC-chip semiconductor pixel detectors. A proton pencil beam with an energy of 220 MeV was utilized to deliver dose rates (DR) ranging from conventional radiotherapy DRs up to 270 Gy/s. A MiniPIX Timepix3 detector equipped with a silicon sensor and integrated readout electronics was used. The chip-sensor assembly and chipboard on water-equivalent back and backing were detached and immersed in the water phantom. The deposited energy, particle flux, DR, and the linear energy transfer (LET(Si)) spectra were measured in the silicon sensor at different positions both laterally across the pencil beam and behind the Bragg peak. At low-intensity beams, the detector is operated in the event-by-event data-driven mode for high-resolution spectral tracking of individual particles. This technique provides precise energy loss response and LET(Si) spectra with radiation field composition resolving power. At higher beam intensities a rescaling of LET(Si) can be performed as the distribution of the LET (Si) spectra exhibits the same characteristics regardless of the delivered DR. The integrated deposited energy and the absorbed dose can be thus measured in a wide range. A linear response of measured absorbed dose was obtained by gradually increasing the delivered DR to reach UHDR beams. Particle tracking of scattered radiation in data-driven mode could be performed at DRs up to 0.27 Gy/s. In integrated mode, the saturation limits were not reached at the measured out-of-field locations despite the delivered DR of over 270 Gy/s. A good agreement was found between measured and simulated absorbed doses.
A. Novak, C. Granja, A. Sagatova, V. Zach, J. Stursa, C. Oancea
This work evaluates the performance of the Timepix3 detector equipped with different semiconductor sensors (GaAs:Cr, CdTe, and Si) for spectral tracking of proton beams. Measurements were performed at the U120-M cyclotron using monoenergetic proton beams (8–31 MeV) and varying incident angles. Detectors were calibrated and operated in data-driven mode with the AdvaPIX interface. Results include deposited energy, track morphology, and LET spectra, with clear dependence on sensor material, thickness, and bias voltage. High-Z materials (CdTe, GaAs:Cr) showed superior energy deposition and stopping power compared to Si. Cluster analysis revealed performance differences in resolution and particle discrimination across sensors. The study supports optimizing sensor choice for high-LET particle detection in applications like ion therapy and space radiation. Future work includes Monte Carlo validation and testing novel materials like SiC and refined GaAs.
St. Gohl, M. Malich, B. Bergmann, P. Burian, C. Granja, E. Heijne, M. Holik, J. Jacubek, J. Janecek, L. Marek, C. Oancea, M. Petro, S. Pospisil, A. Smetana, P. Soukup, D. Turecek, M. Vuolo
A Miniaturized Radiation Monitor (MIRAM) has been developed for the continuous measurement of the radiation field composition and ionizing dose rates in near earth orbits. Compared to currently used radiation monitors, the presented device has an order of magnitude lower weight while being comparable in power consumption and functionality. MIRAM is capable of on‑board real‑time self‑diagnostic. Furthermore, it supports on‑board analysis of the measured data to be able to work autonomously. The dose rate is calculated continuously based on the energy deposition in the Timepix3 detector. For the estimation of the particle species composition of the radiation environment, two methods are applied depending on the current flux. At lower fluxes (<10⁴ particles cm⁻² s⁻¹), a track‑by‑track analysis based on temporal coincidence is applied. At higher fluxes, a less power and memory consuming method is utilized. This method is using the averaged deposited energy per pixel to estimate the electron and proton content of the radiation field.
Jaroslav Šolc, Jan Jakůbek, Lukáš Marek, Cristina Oancea, Jiří Pivec, Jana Šmoldasová, Jiří Tesař, Zdeněk Vykydal
The track structure of the signal measured by the semiconductor pixel detector Timepix3 was modelled in the Monte Carlo MCNP® code. A detailed model at the pixel-level (256 × 256 pixels, 55 × 55 µm² pixel size) was developed and used to generate and store clusters of adjacent hit pixels observed in the measured data because of particle energy deposition path, charge sharing, and drift processes. An analytical model of charge sharing effect and the detector energy resolution was applied to the simulated data. The method will help the user sort the measured clusters and distinguish radiation components of mixed fields by determining the response of Timepix3 detector to particular particle types, energies, and incidence angles that cannot be measured separately.
R. Nabha, O. Van Hoey, C. Granja, A. Parisi, M. De Saint-Hubert, L. Struelens, C. Oancea, E. Sterpin, V. Zach, J. Stursa, A. Rucinski, J. Gajewski, P. Stasica, F. Vanhavere
This study presents a method to evaluate the incident angle and linear energy transfer (LET) of protons using a compact single-layer hybrid pixel detector—Timepix. The study explores correlations between the track shape and the proton incidence angle for varying proton energies (89 MeV and 226.7 MeV) and angles (0° to 75°). Monte Carlo simulations using TOPAS were used to validate the experimental results. The detector, equipped with a 300 μm thick silicon sensor, was irradiated with a mono-energetic proton beam and the resulting cluster shapes analyzed to extract information about incident angles and LET values. A statistical model based on cluster elongation and deposited energy allowed for effective classification and angle estimation. The findings demonstrate the feasibility of using a single-layer Timepix device for angular and LET characterization in proton fields, which could support particle therapy quality assurance and beam monitoring applications.
Carlos Granja, Cristina Oancea, Anna Mackova, Vladimir Havranek, Vaclav Olsansky
We inspected and imaged the delivery of ion microbeams with spatial, time and energy sensitivity. Quantum imaging registration event-by-event is provided in high spatial and time resolution with the position-sensitive semiconductor pixel detector Timepix. The detector is operated as a miniaturized radiation camera for flexible measurements at room temperature and in vacuum. Imaging information on beam profile, spatial and time distribution, flux, homogeneity, and deposited energy for individual beam particles is provided. Focused and scanning beams can be imaged and evaluated online. Single particles are registered by the detector including spectral (deposited energy) information on their position at the µm and µs level. Delivered beams can be characterized also in terms of composition by resolving background and unwanted components such as electrons and X rays from primary beam particles. Ion groups of different energy including doublets or scattered particles can be identified. The technique is applicable for ions of energy above few hundred keV and beams of low intensity, below 10⁵ particles/cm²/s.
Vaclav Olsansky, Carlos Granja, Cristina Oancea, Pavel Krist, Anna Mackova, Vladimir Havranek, Jiri Bila
We investigate the ability of using high-resolution position-sensitive pixel detector and standard non-scanning beams of low-energy protons in air as a flexible tool and simplified technique for density-sensitivity imaging of thin samples. Proton radiography can provide high contrast and low radiation dose delivered to the inspected sample. Density-sensitive contrast response can be provided by a single proton per imaging pixel. For this purpose, we use the silicon semiconductor high-resolution pixel detector Timepix3 to evaluate particle radiography of thin samples with monoenergetic low-energy proton beams from the Tandetron light-ion accelerator. Measurements were performed with various well-defined thin samples. A proton micro beam was used to test and evaluate the technique. Spatial information of the samples is provided by the imaging detector. Density-sensitive contrast is obtained from the measurement of small differences in the deposited energy of transmitted protons across the sample. The transmitted protons are detected with high spatial resolution in the pixel detector. The single particle tracks registered in the detector are analysed by detailed pattern recognition algorithms. Various of these track parameters of spectral response are used for imaging contrast. Resulting proton radiographies for various well-defined thin samples are presented.
C. Oancea, C. Bălan, J. Pivec, C. Granja, J. Jakubek, D. Chvatil, V. Olsansky, V. Chiș
This study characterizes ultra-high dose rate (UHDpulse) electron beams using the MiniPIX Timepix3 Flex detector. It evaluates secondary radiation from pulsed 15–23 MeV electron beams. Using silicon sensors of 100 and 500 μm thickness, the Timepix3 detector measures composition, timing, and spectral characteristics at different lateral beam positions. With a 3.5 μs pulse duration and frame-mode acquisition, the setup provides insights into dose rate (up to 40 Gy/s), flux, and spatial distribution. The Flex version minimizes self-shielding and enables real-time, in-situ monitoring. This flexible detector setup supports future implementation in FLASH therapy and dosimetry protocol development.
C. Granja, J. Jakubek, P. Soukup, M. Jakubek, D. Turecek, L. Marek, C. Oancea, S. Gohl, B. Bergmann, S. Pospisil, M. Malich, M. Vuolo, A. Owens, V. Zach, J. Stursa, D. Chvatil, V. Olsansky, A. Rucinski, J. Gajewski, P. Stasica, Z. Vykydal, J. Solc
The miniaturized radiation camera MiniPIX TPX3 is designed for detailed and wide-range measurements of mixed-radiation fields present in many applications such as radiotherapy and space radiation. The highly integrated instrumentation utilizes a single connector for control and readout for flexible measurements and quick deployment. The device features an option to process the registered data on the same device with limited resolution and basic particle-type resolving power. A novel readout and data processing technique exploits the detector's high granularity and dual per-pixel signal electronics to measure and characterize high-intensity radiation fields with basic particle-type discrimination.
Jacinta Yap, Navrit Bal, Mark Brooke, Carlos Granja, Andrzej Kacperek, Cristina Oancea, Carsten Welsch
Recent advancements in accelerator technology have led the rapid emergence of particle therapy facilities worldwide, affirming the need for enhanced characterisation methods of radiation fields and radiobiological effects. The Clatterbridge Cancer Centre, UK operates a 60 MeV proton beam to treat ocular cancers and facilitates studies into proton-induced radiobiological responses. Accordingly, an indicator of radiation quality is the linear energy transfer (LET), a challenging physical quantity to measure. The MiniPIX-Timepix is a miniaturised, hybrid semiconductor pixel detector with a Timepix ASIC, enabling wide-range measurements of the deposited energy, position and direction of individual charged particles. High resolution spectrometric tracking and simultaneous energy measurements of single particles enable the beam profile, time, spatial dose mapping and LET (0.1 to >100 keV/µm) to be resolved. Measurements were performed to determine the LET spectra in silicon, at different positions along the Bragg Peak (BP). We discuss the experimental setup, preliminary results and applicability of the MiniPIX for clinical environments.
Paulina Stasica, Jakub Baran, Carlos Granja, Nils Krah, Grzegorz Korcyl, Cristina Oancea, Monika Pawlik-Niedźwiecka, Szymon Niedźwiecki, Marzena Rydygier, Angelo Schiavi, Antoni Rucinski, Jan Gajewski
A precise characterization of therapeutic proton pencil beams is essential for the commissioning of any treatment planning system (TPS). The dose profile characterization includes measurement of the beam lateral dose profile in the beam core and far from the beam core, in the so-called low-dose envelope, and requires a sophisticated detection system with a few orders of magnitude dynamic range. We propose the use of a single-quantum-sensitive MINIPIX TIMEPIX detector, along with an in-house-designed holder to perform measurements of the pencil beam dose profile in air and in water. We validated the manufacturer calibration of the MINIPIX TIMEPIX detector in proton beams of various energies and compared the deposited energy spectra to Monte Carlo (MC) simulations. The precision of the lateral dose profile measurements has been systematically validated against Krakow proton facility commissioning data and dose profile simulations performed with MC codes Gate/Geant4 and Fred. We obtained an excellent agreement between MINIPIX TIMEPIX measurements and simulations demonstrating the feasibility of the system for a simple characterization and validation of proton pencil beams. The proposed approach can be implemented at any proton therapy facility to acquire experimental data needed to commission and validate analytical and MC-based TPS.