Diamond detectors for dose and instantaneous dose‐rate measurements for ultra‐high dose‐rate scanned helium ion beams

Background The possible emergence of the FLASH effect—the sparing of normal tissue while maintaining tumor control—after irradiations at dose-rates exceeding several tens of Gy per second, has recently spurred a surge of studies attempting to characterize and rationalize the phenomenon. Investigating and reporting the dose and instantaneous dose-rate of ultra-high dose-rate (UHDR) particle radiotherapy beams is crucial for understanding and assessing the FLASH effect, towards pre-clinical application and quality assurance programs. Purpose The purpose of the present work is to investigate a novel diamond-based detector system for dose and instantaneous dose-rate measurements in UHDR particle beams. Methods Two types of diamond detectors, a microDiamond (PTW 60019) and a diamond detector prototype specifically designed for operation in UHDR beams (flashDiamond), and two different readout electronic chains, were investigated for absorbed dose and instantaneous dose-rate measurements. The detectors were irradiated with a helium beam of 145.7 MeV/u under conventional and UHDR delivery. Dose-rate delivery records by the monitoring ionization chamber and diamond detectors were studied for single spot irradiations. Dose linearity at 5 cm depth and in-depth dose response from 2 to 16 cm were investigated for both measurement chains and both detectors in a water tank. Measurements with cylindrical and plane-parallel ionization chambers as well as Monte-Carlo simulations were performed for comparisons. Results Diamond detectors allowed for recording the temporal structure of the beam, in good agreement with the one obtained by the monitoring ionization chamber. A better time resolution of the order of few μs was observed as compared to the approximately 50 μs of the monitoring ionization chamber. Both diamonds detectors show an excellent linearity response in both delivery modalities. Dose values derived by integrating the measured instantaneous dose-rates are in very good agreement with the ones obtained by the standard electrometer readings. Bragg peak curves confirmed the consistency of the charge measurements by the two systems. Conclusions The proposed novel dosimetric system allows for a detailed investigation of the temporal evolution of UHDR beams. As a result, reliable and accurate determinations of dose and instantaneous dose-rate are possible, both required for a comprehensive characterization of UHDR beams and relevant for FLASH effect assessment in clinical treatments

An Unsupervised Spectrogram Cross-Correlation Method to Assess ELM Triggering Efficiency by Pellets

The high confinement mode (H-mode) is considered the optimal regime for the production of energy through nuclear fusion for industrial purposes since it allows to increase the energy confinement time of the plasma roughly by a factor of two. Consequently, it has been selected at the moment as the standard scenario for the next generation of devices, such as ITER. However, pressure-driven edge instabilities, known as edge localized modes (ELMs), are a distinct feature of this plasma regime. Their extrapolated thermal and particle peak loads on the plasma-facing components (PFC) of the next generation of devices are expected to be so high as to damage such structures, compromising the normal operations of the reactors themselves. Consequently, the induced loads have to be controlled; this can be achieved by mitigating ELMs. A possibility then lays in increasing the ELMs frequency to lower the loads on the PFCs. As already demonstrated at JET, the pellet pacing of ELMs is considered one of the most promising techniques for such scope, and its optimization is therefore of great interest for present and future operations of nuclear fusion facilities. In this work, we suggest a method to access primary pieces of information to perform statistics, assess and characterize the pacing efficiency. The method, tested on JET data, is based on the clustering (k-means) of convoluted signals, using so-called spectrogram cross-correlation, between the measured pellets and ELMs time traces. Results have also been obtained by taking advantage of a new type of diagnostic for measuring the ELMs dynamic, based on synthetic diamond sensors, faster than the standard spectroscopic cameras used at JET

Development and benchmarking of a dose rate engine for raster‐scanned FLASH helium ions

Background:Radiotherapy with charged particles at high dose and ultra-highdose rate (uHDR) is a promising technique to further increase the therapeuticindex of patient treatments. Dose rate is a key quantity to predict the so-calledFLASH effect at uHDR settings. However, recent works introduced varying cal-culation models to report dose rate,which is susceptible to the delivery method,scanning path (in active beam delivery) and beam intensity.Purpose:This work introduces an analytical dose rate calculation engine forraster scanned charged particle beams that is able to predict dose rate from theirradiation plan and recorded beam intensity. The importance of standardizeddose rate calculation methods is explored here.Methods:Dose is obtained with an analytical pencil beam algorithm, usingpre-calculated databases for integrated depth dose distributions and lateralpenumbra. Dose rate is then calculated by combining dose information withthe respective particle fluence (i.e., time information) using three dose-rate-calculation models (mean, instantaneous, and threshold-based). Dose ratepredictions for all three models are compared to uHDR helium ion beam (145.7MeV/u, range in water of approximatively 14.6 cm) measurements performe

Neutron Detectors Based Upon Artificial Single Crystal Diamond

This paper reports about state-of-the-art artificial Single Crystal Diamond (SCD) neutron detectors based on a multilayered structure and grown by chemical vapour deposition (CVD) technique. Multilayered SCD detectors covered with a thin layer of 6LiF allow the simultaneous detection of both slow and fast neutrons and can operate in pulse and current mode. These detectors can also be produced with a thin layer of Boron. Application of SCD detectors to neutron detection around fusion tokamak is reported. Some problems related to the processing of the very fast electrical pulse produced by diamond are addressed and the achieved and foreseen development of the processing electronics is reported as well

Evaluation of a synthetic single-crystal diamond detector for relative dosimetry on the Leksell Gamma Knife Perfexion radiosurgery system

Purpose: To evaluate the new commercial PTW-60019 synthetic single-crystal microDiamond detector (PTW, Freiburg, Germany) for relative dosimetry measurements on a clinical Leksell Gamma Knife Perfexion radiosurgery system. Methods: Detector output ratios (DORs) for 4 and 8 mm beams were measured using a micro- Diamond (PTW-60019), a stereotactic unshielded diode [IBA stereotactic field detector (SFD)], a shielded diode (IBA photon field detector), and GafChromic EBT3 films. Both parallel and transversal acquisition directions were considered for PTW-60019 measurements. Measured DORs were compared to the new output factor reference values for Gamma Knife Perfexion (0.814 and 0.900 for 4 and 8 mm, respectively). Profiles in the three directions were also measured for the 4 mm beam to evaluate full width at half maximum (FWHM) and penumbra and to compare them with the corresponding Leksell GammaPlan profiles. Results: FWHM and penumbra for PTW-60019 differed from the calculated values by less than 0.2 and 0.3 mm, for the parallel and transversal acquisitions, respectively. GafChromic films showed FWHM and penumbra within 0.1 mm. The output ratio obtained with the PTW-60019 for the 4 mm field was 1.6% greater in transverse direction compared to the nominal value. Comparable differences up to 0.8% and 1.0% for, respectively, GafChromic films and SFD were found. Conclusions: The microDiamond PTW-60019 is a suitable detector for commissioning and routine use of Gamma Knife with good agreement of both DORs and profiles in the three directions

Applicazioni del diamante sintetico nella tecnologia dei microsistemi

Dottorato di ricerca in tecnologia dei microsistemi. 12. ciclo. Relatore A. TucciaroneConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

High-quality diamond grown by chemical-vapor deposition: Improved collection efficiency in α-particle detection

Diamond films were grown on silicon by microwave chemical-vapor deposition using a CH4-H2 gas mixture. The crystalline quality of the films was assessed through their α-particle detection performance, a property highly sensitive to film quality, by using a 5.5 MeV 241Am source. A maximum collection efficiency η of 70%, 50% being the average value, was obtained in a 115-μm-thick sample after β-particle irradiation ("priming effect"). Unprimed efficiency η=50% maximum, 30% average, was also obtained on other samples. The dependence of the efficiency and the resolving power on the external electric field was studied as well. The results are interpreted by means of a Monte Carlo analysis of the α-particle detection process. It is concluded that, in the priming process, a saturation occurs of deep defects limiting the as-grown detector performance, and charge collection distance is only limited by grain boundaries located close to the substrate side. Therefore, there is indication that further improvement can be reasonably obtained by increasing film thickness. © 1999 American Institute of Physics

Dosimetro a base di diamante sintetico monocristallino

L’invenzione riguarda un nuovo tipo di dosimetro per radiazioni ionizzanti che utilizza diamante sintetico monocristallino. La struttura del dispositivo (vedi Fig. 1) consiste in: 1. un substrato, eventualmente rimuovibile, di diamante monocristallino (1) 2. uno strato di diamante sintetico monocristalino drogato ed elettricamente conduttore, depositato sul substrato (2) 3. un ulteriore strato di diamante sintetico monocristallino intrinseco (3) 4. un contatto elettrico di natura rettificante oppure ohmico (4) Lo strato di diamante intrinseco costituisce l’elemento sensibile alla radiazione. Lo strato di diamante drogato, che agisce come contatto iniettante, ed il contatto metallico rettificante vengono connessi alla catena di misura

High-quality diamond grown by chemical-vapor deposition: Improved collection efficiency in α-particle detection

Diamond films were grown on silicon by microwave chemical-vapor deposition using a CH4-H2 gas mixture. The crystalline quality of the films was assessed through their α-particle detection performance, a property highly sensitive to film quality, by using a 5.5 MeV 241Am source. A maximum collection efficiency η of 70%, 50% being the average value, was obtained in a 115-μm-thick sample after β-particle irradiation ("priming effect"). Unprimed efficiency η=50% maximum, 30% average, was also obtained on other samples. The dependence of the efficiency and the resolving power on the external electric field was studied as well. The results are interpreted by means of a Monte Carlo analysis of the α-particle detection process. It is concluded that, in the priming process, a saturation occurs of deep defects limiting the as-grown detector performance, and charge collection distance is only limited by grain boundaries located close to the substrate side. Therefore, there is indication that further improvement can be reasonably obtained by increasing film thickness. © 1999 American Institute of Physics

Role of the film texturing on the response of particle detectors based on CVD diamond

Recent improvements in the quality of diamond films grown by Chemical Vapour Deposition (CVD) have made synthetic diamond a very attractive material for detection applications. In this paper, polycrystalline diamond films synthesised by microwave plasma enhanced CVD using a CH4-CO2 gas mixture, previously investigated as particle detectors, have been characterised by X-ray diffraction and Raman spectroscopy. The detector response was measured in vacuo under irradiation with 5.5 MeV α-particle from a 241Am source. A systematic study of the influence of the film structural properties on the detector performance has been carried out by changing the methane concentration in the growth plasma and the deposition temperature. The existence of a correlation between growth conditions, film texturing and detector performance has been demonstrated. Independently of the substrate temperature, (100) orientated films exhibit the lowest detection efficiencies. The meas ured collection distances are smaller than the average grain sizes and seem to be limited by trapping centres within the grains. These results are confirmed by Raman analysis