MeV Electron Beam Research Articles

Stray radiation produced in FLASH electron beams characterized by the MiniPIX Timepix3 Flex detector

This work aims to characterize ultra-high dose rate pulses (UHDpulse) electron beams using the hybrid semiconductor pixel detector. The Timepix3 (TPX3) ASIC chip was used to measure the composition, spatial, time, and spectral characteristics of the secondary radiation fields from pulsed 15–23 MeV electron beams. The challenge is to develop a single compact detector that could extract spectrometric and dosimetric information on such high flux short-pulsed fields. For secondary beam measurements, PMMA plates of 1 and 8 cm thickness were placed in front of the electron beam, with a pulse duration of 3.5 µs. Timepix3 detectors with silicon sensors of 100 and 500 µm thickness were placed on a shifting stage allowing for data acquisition at various lateral positions to the beam axis. The use of the detector in FLEXI configuration enables suitable measurements in-situ and minimal self-shielding. Preliminary results highlight both the technique and the detector’s ability to measure individual UHDpulses of electron beams delivered in short pulses. In addition, the use of the two signal chains per-pixel enables the estimation of particle flux and the scattered dose rates (DRs) at various distances from the beam core, in mixed radiation fields.

Evaluating the accuracy of electron pencil beam dosimetry based on Monte Carlo simulations using homogeneous and heterogeneous phantoms

PurposeThis study aimed to assess the accuracy of the electron pencil beam algorithm (PBA) regarding Monte Carlo (MC) simulations for irradiating homogeneous and heterogeneous phantoms. MethodsThe PBA program was reproduced in the MATLAB software package. The lateral scattering factors were calculated using MC simulations and imported to the PBA program. The line dose values (profile curves) in various depths for a simple water phantom, a slab phantom with different layers, and a heterogeneous phantom with rods equivalent to bone tissue were calculated using PBA and compared to the MC simulation results for 6, 10, and 12 MeV electron beams. The mean differences and root mean square of error (RMSE) were obtained between the PBA and MC calculations. Furthermore, gamma analysis was used to compare the profile doses of PBA calculations with MC simulations. ResultsThe mean differences between the PBA and MC dose calculations were less than 1% for 10 and 12 MeV electron energies, and lower than 2% for the 6 MeV electron irradiation in all the assessed phantoms. The profile dose calculations showed that the separation of two isodose curves was less than 2 mm in central regions of the fields and less than 3 mm in the fields’ edge/penumbra regions and inhomogeneity interfaces. The gamma pass rate values ranged from 94.1 to 100% (average of 96.4%) in different phantoms, depths, and energy ranges. ConclusionThe PBA provided acceptable accuracy for radiotherapy electron dose calculations in a water phantom, slab phantom (with different materials), and heterogeneous phantom compared to MC dose simulations, as a reference dose calculation method.

Облучение быстрыми нейтронами как способ преодоления радиорезистентности плоскоклеточного рака полости рта кошек: пилотное исследование

For the study 4 cats with unresectable oral squamous cell carcinoma were treated with combina-tion of neutron and electron radiations. 3 cats had T2b and one had T3b stage. The first phase of treatment was performed with 14 MeV fast neutron beam, fraction dose varied from 1.0 to 1.3 Gy, 3 fractions a week, 3-5 fractions in total; in the second phase the animals were irradiated with 10 MeV electron beam, using same fractionation, fraction dose varied from 4 Gy, up to total dose of 8-36 Gy. In the course of treatment, most cats had partial or complete anorexia, the duration of which did not exceed two days, it was well controlled by antidepressants (mirtazapinum). Visual assessment and computed tomography performed from 13 to 30 days after treatment comple-tion demonstrated showed the significant regression of tumor volume (30-67%) in all cases. 3 out of 4 animals were alive at the time of the study, average follow-up period was 84 days, maximum follow-up period was 160 days. Radiation damage was limited to local alopecia followed by leu-kotrichia.

Development of dosimetric procedures for experimental ultra-high dose rate irradiation at a clinical linear accelerator

As radiotherapy using ultra-high dose rates has gained new interest, the dosimetric challenges arising at these conditions needs to be addressed. Ionization chambers suffer from a large decrease in ion collection efficiency due to ion recombination, making on-line dosimetry difficult. In this work we present experimental setups and dosimetric procedures for FLASH irradiation of cells, zebrafish embryos and small animals using a 10 MeV electron beam at a modified clinical linear accelerator, and describe the dosimetric steps required to initiate clinical trials. The dosimetric equipment used for our pre-clinical experiments consisted of radiochromic film, thermoluminescent dosimeters, a Farmer-type ionization chamber and phantom material mimicking the experimental setup for irradiation. In preparation for small animal irradiation, dose profiles and depth dose curves were measured for all collimator sizes. The average dose rates were ≥620 Gy/s, ≥640 Gy/s and ≥400 Gy/s for cells, zebrafish embryos and small animals, respectively.

Emission of fused silica and KBr samples in the UV and visible spectral ranges under irradiation with 2.7 MeV electrons

Fused silica and KBr samples were irradiated with a 2.7 MeV electron beam. The emission of fused silica and KBr samples in the UV and visible regions was studied under various experimental conditions. Numerical simulation of optical emission was carried out using the GEANT4 computer platform. Simulations of energy spectra and angular distributions of the beam electrons were performed for different target thicknesses. The results reveal the effect of scattering of the beam electrons on the angular distribution of Cherenkov radiation in fused silica samples with thicknesses exceeding the electron path length.

Photon beam dose enhancement in AuNP AC tumour through energy moderation of a 6 MeV electron beam: A Monte Carlo study

PurposeTo use Monte Carlo (MC) simulations (BEAMnrc and DOSXYZnrc) to investigate different moderators to slow down 6 MeV electrons before striking a tungsten bremsstrahlung target. The generated x-ray beam is then used to study the dose-effect when the beam traverses a gold-nanoparticle (AuNP) enriched tumour. Materials and methodsIn this study, the 6 MV linear accelerator model was without a beam flattening filter. The BEAMnrc code was used to simulate the 6 MeV electron beam traversing through water or carbon moderators of various thicknesses before striking a thin tungsten target to produce photon beams with effective energies less than the original 6 MV beam (without any moderation). For each beam, a phase-space (PHSP) file was scored to be used in subsequent DOSXYZnrc simulations. The DOSXYZnrc code was utilised to obtain percentage depth dose (PDD) and dose distributions in a 40 × 40 × 40 cm3 water phantom for each beam. All DOSXYZnrc simulations were repeated but with a tumour model near the surface of the water phantom. Dose enhancement effects (DEFs) were calculated in the tumour model as the ratio of the dose in the tumour with and without gold-nanoparticles (AuNPs) seeded into the tumour at a concentration of 7 mg/g. ResultsWater or carbon moderators slowed the primary 6 MeV electron beam down, resulting in lower energy photon beam spectra generated in the tungsten target. Significant dependence of DEFs on the mean energy of the resulting x-ray beams was shown as a function of moderator thickness. For beams moderated to kilovolt energies, the effect was more enhanced as anticipated. DEF values ranged between 1.01 and 1.075 for various moderator/bremsstrahlung x-ray target combinations. The highest DEF (1.075) was obtained for a moderator consisting of either 2.5 cm water or 1.4 cm carbon to slow the 6 MeV electrons down before hitting the tungsten target of 0.07 cm thickness. ConclusionsCarbon and water moderators can effectively slow electrons down before using them to generate low energy bremsstrahlung x-rays to enhance the dose in a tumour seeded with AuNPs. DEF's of up to 1.075 can be obtained whilst using beams of energy lower than 1 MV.

Radiation-stimulated oxidation of the plastic surface in a water-air flow

Radiation-stimulated surface oxidation of polyolefin powders and films is considered from the point of view of enhancing their adhesion to building materials. The technological convenience of oxidative modification in the presence of water is noted. Variants of practical in-line oxidation with vertical and horizontal directions of the electron beam are shown. Using road bitumen and a test adhesive tape, the adhesion of 0.1 mm polyethylene and polypropylene films was tested under single-layer irradiation in air, as well as inside an energy-absorbing filter in a position corresponding to the maximum depth-dose distribution for a 3 MeV electron beam. The results obtained indicate that a more stable enhancement of adhesion is provided when irradiation occurs in air in the presence of water or an aqueous solution of formic acid.

Behavior of mesoporous silica under 2 MeV electron beam irradiation

This work deals with the evolution of the mesoporous structure of two silicas MCM-41 and SBA-15 under a 2 MeV electron beam as a function of the dose (0–5 GGy). For a dose of 2 GGy, the pore volume of the two materials decreases significantly by 40–45%. The irradiation-induced porosity closure is significantly more effective on smaller pores, resulting in a loss of the mesoporous network concerning MCM-41 (pore diameter ∼ 3.8 nm) and the conservation of the SBA-15 one (pore diameter ∼ 7.0 nm). The mechanism of silica porosity closure/collapse has not been fully identified, but it might result from damage effects as “Knock-on” processes. From a technological point of view, this phenomenon could be exploited for RadioNuclides (RN) encapsulation in a self-evolving porous material.

Dosimetric accuracy of a cross-calibration coefficient for plane-parallel ionization chamber obtained in low-energy electron beams using various cylindrical dosimeters

Abstract Introduction: The accuracy of the cross-calibration procedure depends on ionization chamber type, both used as reference one and under consideration. Also, the beam energy and phantom medium could influence the precision of cross calibration coefficient, resulting in a systematic error in dose estimation and thus could influence the linac beam output checking. This will result in a systematic mismatch between dose calculated in treatment planning system and delivered to the patient. Material and methods: The usage of FC65-G, CC13 and CC01 thimble reference chambers as well as 6, 9, and 15 MeV electron beams has been analyzed. A plane-parallel PPC05 chamber was calibrated since scarce literature data are available for this dosimeter type. The influence of measurement medium and an effective point of measurement (EPOM) on obtained results are also presented. Results: Dose reconstruction precision of ~0.1% for PPC05 chamber could be obtained when cross-calibration is based on a thimble CC13 chamber. Nd,w,Qcross obtained in beam ≥ 9MeV gives 0.1 – 0.5% precision of dose reconstruction. Without beam quality correction, 15 MeV Nd,w,Qcross is 10% lower than Co-60 Nd,w,0. Various EPOM shifts resulted in up to 0.6% discrepancies in Nd,w,Qcross values. Conclusions: Ionization chamber with small active volume and tissue-equivalent materials supplies more accurate cross-calibration coefficients in the range of 6 – 15 MeV electron beams. In the case of 6 and 9 MeV beams, the exact position of an effective point of measurement is of minor importance. In-water cross-calibration coefficient can be used in a solid medium without loss of dose accuracy.

Personalized 3D-printed anthropomorphic phantoms for dosimetry in charged particle fields

Anthropomorphic phantoms used for radiation dose measurements are designed to mimic human tissue in shape, size, and tissue composition. Reference phantoms are widely available and are sufficiently similar to many, but not all, human subjects. 3D printing has the potential to overcome some of these shortcomings by enabling rapid fabrication of personalized phantoms for individual human subjects based on radiographic imaging data. Objective. The objective of this study was to test the efficacy of personalized 3D printed phantoms for charged particle therapy. To accomplish this, we measured dose distributions from 6 to 20 MeV electron beams, incident on printed and molded slices of phantoms. Approach. Specifically, we determined the radiological properties of 3D printed phantoms, including beam penetration range. Additionally, we designed and printed a personalized head phantom to compare results obtained with a commercial, reference head phantom for quality assurance of therapeutic electron beam dose calculations. Main Results. For regions of soft tissue, gamma index analyses revealed a 3D printed slice was able to adequately model the same electron beam penetration ranges as the molded reference slice. The printed, personalized phantom provided superior dosimetric accuracy compared to the molded reference phantom for electron beam dose calculations at all electron beam energies. However, current limitations in the ability to print high-density structures, such as bone, limited pass rates of 60% or better at 16 and 20 MeV electron beam energies. Significance. This study showed that creating personalized phantoms using 3D printing techniques is a feasible way to substantially improve the accuracy of dose measurements of therapeutic electron beams, but further improvements in printing techniques are necessary in order to increase the printable density in phantoms.

Septum magnet design for compact storage ring

Compact storage rings have been recently constructed or are under construction for industrial or medical applications. Such compact rings operate at tens to hundreds MeV and their footprint is of the order of few meters. Since the size is a critical issue for many applications, the accelerator components installation is extremely dense. Beam injection into such a ring, therefore, takes place with a large bending angle. PAL-EUV is a 400 MeV synchrotron under construction at Pohang Accelerator Laboratory for semiconductor industries. The PAL-EUV accelerator consists of a 20 MeV injector linac, a booster ring and a 400 MeV storage ring, installed in a 15 m by 15 m area enclosed by a concrete wall. Three Lambertson septum magnets are used for the electron injection and extraction between the injector linac, the booster ring and the storage ring. The injection septum in the booster ring bends a 20 MeV electron beam transferred from the injector linac by 60°. The septum magnets for booster ring extraction and storage ring injection bend a 400 MeV beam by 30°. Due to the large bending angle of the septum magnets, the holes for the circulating beams extend to the outer side of the return yokes. In addition, the 2 mm septum thickness for the three septa is a concern for the leakage of the magnetic field which may generate higher order field multipoles in the field-free region of the circulating beam. In this article, we discuss the leakage fields in the septum magnets and how to minimize the impact on the circulating electron beams in the rings.

Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study

Carbon-centered radicals have been randomly generated on the chains of poly(acrylic acid), PAA, the simplest synthetic anionic polyelectrolyte, by pulse-irradiating its dilute, oxygen-free aqueous solutions by 6 MeV electron beam. In some experiments, oligo(acrylic acid), OAA, and propionic acid, PA, were used as PAA models. Recombination kinetics of PAA radicals has been followed by fast spectrophotometry. A strong pH dependence of radical lifetime on pH, and thus on the linear charge density due to deprotonated carboxylate groups, has been confirmed, while a weaker amplitude of pH dependence was observed for OAA and PA. Decay kinetics of PAA radicals in the protonated state, at pH 2, have been studied in some detail. At moderate doses of ionizing radiation, resulting in a moderate average initial number of radicals per chain, ZR0, the decay can be satisfactorily described by a second-order kinetic model, but a somewhat better fit is obtained by using a dispersive kinetics approach. While for a constant polymer concentration the reciprocal half-lives are proportional to the initial radical concentrations, such a data series for different PAA concentrations do not overlap, indicating that the overall radical concentration is not the decisive factor controlling the kinetics. Arranging all data, in the form of second-order rate constants, as a function of the average initial number of radicals per chain allows one to obtain a common dependence. The latter seems to consist of two parts: a horizontal one at low ZR0 and another one of positive slope at higher ZR0. This is interpreted as two kinetic regimes where two distinct reactions dominate, intermolecular and intramolecular recombination, respectively. Comparison of the low ZR0 data with calculations based on the translational diffusion model indicate that the latter is not the rate-controlling process in intermolecular recombination of polymer radicals; segmental diffusion is the more likely candidate.

Effect of irradiation on volatile compound profiles and lipid oxidation in chicken powder seasoning

The effects of two types of industrial irradiation sources (10 MeV electron beam (EB) and gamma ray (GR), irradiation at 4 kGy and 7 kGy, respectively) on off-odor, volatile compounds, and lipid oxidation in chicken powder seasoning were studied. Irradiation induced off-odor and lipid oxidation in a dose-dependent manner. EB was better than GR at the same dose, with less off-odor and lower peroxide value (POV) and thiobarbitunic acid reactive substance (TBARS) values. GC/MS analysis revealed the presence of 121 volatile compounds, including 113 in non-irradiated chicken powder seasoning followed by 98 in EB 4 kGy, 91 in EB 7 kGy, 80 in GR 4 kGy, and 76 in GR 7 kGy. Irradiation decreased terpenes and terpenoids, and increased aldehydes/alkenes and induced formation of E−1,8-dodecadiene, which correlated to increasing radiation dose. EB induced higher alkenes, terpenes, and terpenoids as well as lower aldehydes than GR at the same dose. In GR 7 kGy-irradiated chicken powder seasoning, 3-octen-2-one, 3,5-octadien-2-one, hexanal, and hexanoic acid were higher than other irradiation treatments. These results suggest that dose contributes to off-odor intensity, and EB has an advantage over GR for chicken powder seasoning irradiation, with more original volatile compounds, lower off-odor, and less lipid oxidation.

Skin Dose Distributions from Total Skin Electron Irradiation Therapy (TSET)

Skin Dose Distributions from Total Skin Electron Irradiation Therapy (TSET)

Benzophenone doped polydimethylsiloxane: Resist platform for MeV electron beam lithography assisted microlens array fabrication

Poly-dimethylsiloxane (PDMS) is known to provide ubiquitous platform for micro Total Analysis System (μ-TAS) and Lab-On-Chip (LOC) development. Although soft lithography is extensively accepted as a fabrication tool for PDMS, direct write lithography techniques also have drawn considerable attention due to some of its own advantages. Even though e-beam lithography in PDMS is reported previously, the present manuscript reveals establishment of doped PDMS as a positive tone, self-standing and self-developable resist platform for 6 MeV e-beam lithography in normal ambience. For microstructures fabrication, undoped PDMS and photoinitiator doped PDMS as resist materials are processed using contact printing mode lithography with use of the mask containing array of circles on it. Effects of lithography processing parameters on various resist compositions are investigated to achieve improved geometry and surface profile of the fabricated microstructures. Lithographic investigations on the undoped PDMS shows microstructures with sloppy sidewalls depicting inverted bell shape geometry and cone like nanostructures inside it deteriorating surface profile. Whereas in case of doped PDMS cone like nanostructures are completely vanished and inverted bell shape geometry transformed into clean and uniform concave shape profile, which is then identified as finely produced micro lens array (MLA). The lensing quality of MLA is tested and the images produced by MLA are clear and uniform in size and shape, which confirms formation of microlenses accountable as an optical component in many applications. The observed concave geometry of fabricated MLA is resulted out of energy gradient generated during the e-beam exposure of resist stamp through mask. Similarly, an electrostatic interaction is recognized as governing mechanism for e-beam interaction with PDMS. Photoinitiator plays crucial role in energy absorption and distribution which resulted in seamless control over formation of lateral and vertical dimensions thereby giving optical smoothness to surface of MLA. The optimized lithographic parameters and composition of the resist platform, can be used to fabricated MLA with fine imaging quality and desired location of focal plane according to demand of application.

Depth-dose profiles in continuous and discontinuous materials of food products and medical devices irradiated by 10 MeV electron beam

Depth-dose profiles in continuous and discontinuous materials of food products and medical devices irradiated by 10 MeV electron beam

A novel real-time shapeable soft rubber bolus for clinical use in electron radiotherapy

We have developed soft rubber (SR) bolus that can be shaped in real-time by heating flexibly and repeatedly. This study investigated whether the SR bolus could be used as an ideal bolus, such as not changing of the beam characteristics and homogeneity through the bolus and high plasticity to adhere a patient in addition to real-time shapeable and reusability, in electron radiotherapy. Percentage depth doses (PDDs) and lateral dose profiles (LDPs) were obtained for 4, 6, and 9 MeV electron beams and were compared between the SR and conventional gel boluses. For the LDP at depth of 90% dose, the penumbra as lateral distance between the 80% and 20% isodose lines (P 80−20) and the width of 90% dose level (r 90) were compared. To evaluate adhesion, the air gap volume between the boluses and nose of a head phantom was evaluated on CT image. The dose profiles along the center axis for the 6 MeV electron beam with SR, gel, and virtual boluses (thickness = 5 mm) on the head phantom were also calculated for the irradiation of 200 monitor unit with a treatment planning system and the depth of the maximum dose (d max) and maximum dose (D max) were compared. The PDDs, P 80−20, and r 90 between the SR and gel boluses corresponded well (within 2%, 0.4 mm, and 0.7 mm, respectively). The air gap volumes of the SR and gel boluses were 3.14 and 50.35 cm3, respectively. The d max with SR, gel and virtual boluses were 8.0, 6.0, and 7.0 mm (no bolus: 12.0 mm), and the D max values were 186.4, 170.6, and 186.8 cGy, respectively. The SR bolus had the equivalent electron beam characteristics and homogeneity to the gel bolus and achieved excellent adhesion to a body surface, which can be used in electron radiotherapy as an ideal bolus.

Radiotherapy dosimetry parameters intercomparison among eight gel dosimeters by Monte Carlo simulation

Dosimetry in radiotherapy is extremely important to guarantee effectiveness of the treatment, as described by quality assurance procedures. The main dosimeter framework proposed by International Protocols is commonly based on determinations of in-water absorbed dose. Gel dosimetry, mainly based on liquid water, offers the unique characteristic that the phantom constitutes itself the radiosensitive material. This study reports on the suitability of gel dosimetry formulations, typically implemented for clinical purposes, evaluating dosimetry outputs by means of PENELOPE and FLUKA Monte Carlo simulations, along with experimental data. The effects on the absorbed dose distributions due to variation in the mass density and the mean excitation energy are calculated for BANG®, Fricke, ITABIS, MAGIC, NBT-Pluronic, NIPAM, PAGAT, and PRESAGE formulations at irradiations with 6 and 15 MV photon and 6 MeV electron beams. Dosimetry parameters for photon and electron beams are calculated, and effects due to variations in mass density and mean excitation energy are carefully investigated. According to the results obtained from Monte Carlo simulations, along with dose profile comparisons with simulations of in-water irradiations, and comparisons with experimental data, all studied gel dosimetry formulations are capable of assessing reliable dosimetry outputs extracted from 3D dose distributions, even with uncertainties in their mass density or mean excitation energy of ±10%.

Simulating the electric field distribution in medium-voltage cables of cross-linked polyethylene/Cu nanocomposites irradiated by E-beam with reference to the XLPE market

ABSTRACT In this paper, the distribution of the electric field of medium voltage (MV) underground cable insulation made of polyethylene/copper nanoparticles (XLPE/Cu) is investigated. Three methods were established for copper nanoparticles (CuNPs) synthesis such as the alkaline reduction process, electrolysis process and metal displacement reaction. Ultraviolet–visible spectra, X-ray diffraction, and transmission electron microscopy (TEM) were used to classify the obtained CuNPs. The XLPE/Cu films with different CuNP weight content (0%, 1%, 3% and 5%) were subjected to a 3 MeV electron beam (EB) with different doses (0, 15, 20 and 25 kGy). The optimum AC/DC conductivity (AC 2 × 10−3 S m−1, DC 4.63 × 10−2 S m−1) in minimum relative permittivity (2.05) achieved for (XLPE/5-Cu) 25 kGy that is has a CuNP content of 5 wt-% and irradiated at 25 kGy. The electric field distribution in the middle of the (XLPE/5-Cu) 25 kGy sample is maximum uniform than at the top or bottom.

Demonstration of high energy electron radiography with sub-micron spatial resolution

As a new scheme, High Energy Electron Radiography (HEER) was considered as an effective diagnostic tool in the mesoscale sciences due to its high spatial temporal resolution and large area density diagnostic range. Some improvements were implemented to achieve high spatial resolution using a 50 MeV electron beam in Lanzhou, China. These included improving the uniformity of the beam transverse distribution, optimizing the energy spread and increasing the magnet lens magnification. Then the HEER image was collected by a CCD camera with image processing program and in-situ spatial resolution optimization adjustment program. To the best of our knowledge, the achieved spatial resolution of 0.8 μm constitutes a world record. The details of this experiment are described in this publication.