Research articles, complete author lists, abstracts and available manuscripts. Open a publication for its permanent page, DOI and downloadable citations.
Publications (8)
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.
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.
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.
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.
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.
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.
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.
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.