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Publications (6)
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.
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.
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.
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.
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.
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.