MeV Electron Beam Research Articles

Ultra-High Dose Rate FLASH Effect on Head and Neck Cancer Cells and Normal Salivary Gland in Mice

<h3>Purpose/Objective(s)</h3> Ultra-high dose rate irradiation (FLASH) is a novel therapeutic modality that has been reported to spare tissues compared to conventional dose rate. We aimed to investigate the effect of FLASH on head and neck (H&N) cancer cells and salivary gland dysfunction caused by radiotherapy. <h3>Materials/Methods</h3> H&N cancer cells (HSG and FaDu) were irradiated with 10 MeV electron beam at a dose rate of 132.2Gy/s (FLASH) or 0.1Gy/s (CONV), by a modified clinic linear accelerator. The irradiated dose was confirmed with EBT-XD film, and 3, 7, and 11 Gy were irradiated. We evaluated the cell cycle and the surviving fraction of cells with clonogenic assays. We administered single dose head and neck irradiation to mice with a 6 MeV electron beam at dose rate of 105.6-126 Gy/s (FLASH) or 0.03Gy/s (CONV), using a modified linear accelerator. The irradiated dose was confirmed with EBT3 film, and 9-76 Gy and 10-30 Gy were irradiated for FLASH and CONV, respectively. Parotid and submandibular glands were obtained from mice at 3 and 30 days after irradiation. Immunohistological examination and apoptotic assays were conducted to assess the radiation response. <h3>Results</h3> The proportion of sub G0/G1 was higher in the FLASH group, and the surviving fraction was significantly decreased in FLASH through every dose range. At three days post-irradiation, both 10 Gy and 30 Gy irradiated groups showed a greater number of salivary cells and increased expression of AQP5 in FLASH compared to conventional irradiated mice. As a late toxicity (30 days of irradiation), fibrosis did not show any significant difference, although FLASH group received much higher radiation dose. There was no difference in apoptosis between groups on post 3 days, but FLASH showed significantly less degree of apoptosis on 30 days after irradiation. <h3>Conclusion</h3> This study demonstrates that FLASH irradiation strengthens the therapeutic effect for H&N cancers and attenuates radiation-induced salivary gland damage. Further research is needed on the biological mechanisms involved.

A prototype low-cost secondary standard calorimeter for reference dosimetry with ultra-high pulse dose rates.

Ultra-high pulse dose rate modalities present significant dosimetry challenges for ionisation chambers due to significant ion recombination. Conversely, calorimeters are ideally suited to measure high dose, short duration dose deliveries and this work describes a simple calorimeter as an alternative dosemeter for use in the clinic. Calorimeters were constructed featuring a disc-shaped core and single sensing thermistor encased in a 3D-printed body shaped like a Roos ionisation chamber. The thermistor forms one arm of a DC Wheatstone bridge, connected to a standard DMM. The bridge-out-of-balance voltage was calibrated in terms of temperature. A graphite-core calorimeter was calibrated in terms of absorbed dose to water (J/kg) in Co-60 and conventional 6, 10 and 15 MV X-rays. Similarly, an aluminium-core calorimeter was calibrated in a conventional 20 MeV electron beam and tested in a research high dose per pulse 6 MeV electron beam. Calorimeters were successfully calibrated in terms of absorbed dose to water in conventional radiotherapy beams at approximately 5 Gy/min with an estimated uncertainty of ±2-2.5% (k = 2), and performed similarly in a 6 MeV electron beam delivering approximately 180 Gy/s. A simple, low-cost calorimeter traceably calibrated to existing primary standards of absorbed dose could be used as a secondary standard for dosimetry for ultra-high pulse dose rates in the clinic. Secondary standard calorimeters for routine measurements are not available commercially; this work presents the basis of a simple, low-cost solution for reference dosimetry for ultra-high pulse dose rate beams.

Luminescence of MgF2-WO3 ceramics synthesized in the flux of 1.5 MeV electron beam

The results of comparative analysis of optical properties of MgF2 single crystals and MgF2 ceramics, non-doped and doped with tungsten trioxide obtained in the process of high-speed radiation synthesis in air under a flux of 1.5 МеV electrons, are presented.The synthesized ceramics are found to have a high degree of crystallinity, their elements composition is close to stoichiometric, and the phase composition is a rutile lattice.Using time-resolved spectroscopy, it was shown that the initial defectiveness of as-synthesized ceramics samples is represented by emission centers belonging to WO3 complexes and radiation defects of F2- types with spectral-kinetics parameters similar to those in irradiated by ionizing radiation MgF2 single crystals. The ratio between these types of defects is determined by the temperature and luminescence excitation method and the ratios between dopant and co-dopant (LiOH).In MgF2 ceramics samples, being exposed to ionizing radiation, two radiative channels of relaxation of electronic excitations were found: T-So (triplet-singlet) emission transition in self-trapped excitons (STE) at 3.2 eV and recombination of F–H Frenkel pairs accompanied with the emission at 4.0 eV. The temperature dependences of these channel efficiency in the range of 5–300 K are similar to those ones observed in MgF2 single crystals.

In-situ preparation of gel polymer electrolytes in a fully-assembled lithium ion battery through deeply-penetrating high-energy electron beam irradiation

Several in-situ preparation methods of gel polymer electrolytes (GPEs) to develop long-lasting and safe lithium ion batteries (LIBs) recently have been reported. However, the reported in-situ methods still have technical gaps for practical industrial uses in terms of processing time, integrity with the current production line, and scalability. Here, we report an in-situ method to prepare crosslinked poly(vinylene carbonate-co-cyanoethyl acrylate) (PVCEA) GPEs using 10 MeV electron beam (EB) irradiation in a fully-assembled metallic housing LIB that can be processed in a short time without any initiator or thermal treatment. The successful in-situ formation of PVCEA GPEs was achieved at absorbed doses above 16 kGy (irradiation time of 56 s), leading to intimately integrated GPEs with the electrodes, while ensuring stable charge and discharge performance. The prepared PVCEA GPE exhibited a higher transference number (tLi+ = ca. 0.53) and a wider electrochemical operation window (up to 5.0 V) than those of a liquid electrolyte (LE), while providing good ionic conductivity (1.17 mS/cm at 20 °C). Furthermore, the PVCEA GPE-based LIB prepared at an optimized dose of 16 kGy showed comparable retention capacity of 83 % at 0.5C to the conventional LE-based LIB after 300 cycles at 25 °C, and more importantly, better cycling durability at elevated temperature of 60 °C in comparison to the LE-based LIB. This study suggests that the combination of radiation-sensitive precursor formulation and high-energy EB with high penetration ability can provide a promising solution for industrial production of high-performing and safe LIBs.

Radiation Damage in Polyethylene Naphthalate Thin-Film Scintillators.

This paper describes the scintillation features and the radiation damage in polyethylene naphthalate 100 µm-thick scintillators irradiated with an 11 MeV proton beam and with a 1 MeV electron beam at doses up to 15 and 85 Mrad, respectively. The scintillator emission spectrum, optical transmission, light yield loss, and scintillation pulse decay times were investigated before and after the irradiation. A deep blue emission spectrum peaked at 422 nm, and fast and slow scintillation decay time constants of the order of 1–2 ns and 25–30 nm, respectively, were measured. After irradiation, transmittance showed a loss of transparency for wavelengths between 380 and 420 nm, and a light yield reduction of ~40% was measured at the maximum dose of 85 Mrad.

Raman spectroscopy of electron irradiated Multi-Walled Carbon Nanotube for dosimetry purposes

In this experimental work, dosimetry characteristics of Multi-Walled Carbon Nanotube (MWCNT), including linearity, repeatability, and long-term stability, were carried out using a 10 MeV electron-beam at various absorbed doses of 0, 10, 20, 30, 50, 80, 150, and 200 kGy at room temperature by Raman spectroscopy. HRTEM, FESEM, and FTIR tests were performed to investigate changes in the atomic and molecular structures in the material at various doses. Results of the HRTEM, and FESEM tests were in good accordance with the experimental data in justifying the dosimeter behavior. FTIR analysis confirmed the presence of C–C, C–O, CC, CO, CH, CH2, and OH functional groups in the samples. The samples were analyzed by Raman spectroscopy to identify defects created in the carbon atoms of the MWCNT. Results showed that the amount of ID/IG quantity, as the dosimeter response, versus absorbed dose was linear up to 50 kGy with a standard deviation of 9.8%. Finally, fading analysis was carried out after 4 months, where a significant change in the dosimeter response was observed. Our findings show the benefits of Raman spectroscopy to measure the response of the dosimeter as quickly as possible. Also, it is recommended to study on the fading effect at various time intervals.

Rhodotron and rotating target: A solution towards micro-spot for high energy and high dose rate bremsstrahlung sources

High energy over MeV bremsstrahlung sources that employ normal conducting radio frequency linear accelerators have expanding applications in industrial computerized tomography (CT) for non-destructive inspection and evaluation. The X-ray spot size that mainly affects the imaging quality is yet limited by the electron beam width in the high resolution CT systems. In a short exposure time, high beam power is required to generate sufficient photons to improve the signal to noise ratio of imaging. However, with ∼kW level of average beam power these linear accelerators usually have a beam spot size over 1 mm since the temperature rising due to the beam energy deposition in the target should be far below its melting point. We propose a concept of using a Rhodotron-based accelerator to provide high power electron beams in a long duration pulse and a rotating target to mitigate the overheating issue, such that the gap between micro-spot and high dose rate can be bridged in the high energy bremsstrahlung sources. This article presents an in-depth simulation work to discuss and evaluate this scheme of X-ray source. The simulations of beam dynamics in the accelerator and bremsstrahlung process in the target predict the generated X-rays with a spot size as small as 68 μm at full-width half-maximum and a dose rate as high as 4700 cGy/min from a 9 MeV electron beam interacting with a 1 mm thickness tantalum target. Further thermal analysis in the rotating target indicates a significant improvement of beam power handling in comparison with the conventional stationary one.

Development of a real-time in vivo dosimetry tool for electron beam therapy using a flexible thin film solar cell coated with scintillator powder.

A real-time solar cell based in vivo dosimetry system (SC-IVD) was developed using a flexible thin film solar cell and scintillating powder. The present study evaluated the clinical feasibility of the SC-IVD in electron beam therapy. A thin film solar cell was coated with 100 mg of scintillating powder using an optical adhesive to enhance the sensitivity of the SC-IVD. Calibration factors were obtained by dividing the dose, measured at a reference depth for 6-20 MeV electron beam energy, by the signal obtained using the SC-IVD. Dosimetric characteristics of SC-IVDs containing variable quantities of scintillating powder (0-500 mg) were evaluated, including energy, dose rate, and beam angle dependencies, as well as dose linearity. To determine the extent to which the SC-IVD affected the dose to the medium, doses at R90 were compared depending on whether the SC-IVD was on the surface. Finally, the accuracy of surface doses measured using the SC-IVD was evaluated by comparison with surface doses measured using a Markus chamber. Charge measured using the SC-IVD increased linearly with dose and was within 1% of the average signal according to the dose rate. The signal generated by the SC-IVD increased as the beam angle increased. The presence of the SC-IVD on the surface of a phantom resulted in a 0.5%-2.2% reduction in dose at R90 for 6-20 MeV electron beams compared with the bare phantom. Surface doses measured using the SC-IVD system and Markus chamber differed by less than 5%. The dosimetric characteristics of the SC-IVD were evaluated in this study. The results showed that it accurately measured the surface dose without a significant difference of dose in the medium when compared with the Markus chamber. The flexibility of the SC-IVD allows it to be attached to a patient's skin, enabling real-time and cost-effective measurement.

Parametric X-ray radiation from nanopowders

The first observation of Parametric X-ray Radiation (PXR) produced in a crystalline powder constituted of crystallites whose largest dimensions are of the order of some nanometers is reported. PXR was registered during the interaction of a 7 MeV electron beam with a platinum powder. The experimental results were compared with the kinematical theory showing a good agreement concerning the position, form, and intensity of all observed PXR spectral peaks. Finally, an analysis of the influence of crystallite dimensions on the PXR peak full width hall maximum (FWHM) and PXR peak intensity was performed.

Natural Baicalein-Rich Fraction as Radiosensitizer in Combination with Bismuth Oxide Nanoparticles and Cisplatin for Clinical Radiotherapy.

PurposeChemotherapy has been used in conjunction with radiation therapy to improve the treatment outcomes of cancers. Cisplatin (Cis) is a standard treatment that has been used as a chemotherapeutic drug in medical settings. However, the possibility of complications constrains the treatment due to the exposure of healthy organs to unnecessary radiation and the drugs’ toxicities. As a result, researchers have been looking for non-toxic chemotherapeutic agents which can be used as radiosensitizers, possibly produced from natural derivatives and nano sized materials.MethodsBRF, Cis, and BiONPs were irradiated individually and in combinations with 6 MV of photon beam and 6 MeV of electron beams with 0 to 10 Gy radiation doses on MCF-7, MDA-MB-231, and NIH/3T3 cell lines. Then, the experimental sensitization enhancement ratios (SER) of each treatment obtained were compared to the theoretical dose enhancement factor (DEF). The interactions within the BRF-BiONPs (BB) and BRF-Cis-BiONPs (BCB) combinations were also estimated using the Combination Index (CI).ResultsBRF induced radiosensitization in all cells under 6 MV photon beam (SER of 1.06 to 1.35), and MDA-MB-231 cells only under 6 MeV electron beam (SER = 1.20). The highest SER values for BiONPs and Cis were obtained from MCF-7 cells under a 6 MeV electron beam (SER of 1.50 and 2.24, respectively). The theoretical DEFs were generally lower than the experimental SERs. Based on the SER and CI relationships, it was estimated that BB and BCB therapy methods interacted in either a synergistic or additive manner.ConclusionThe BRF is found to induce relatively less radiosensitization effects compared to the BiONPs and Cis. The BB and BCB combinations have shown better effects with potential for becoming competently suitable radiosensitizers in breast cancer therapies.

Validation of Monte Carlo-based calculations for megavolt electron beams for IORT and FLASH-IORT

In Intra-Operative Radiation Therapy (IORT) the tumour site is surgically exposed and normal tissue located around the tumour may be avoided. Electron applicators would require large surgical incisions; therefore, the preferred mechanism for beam collimation is the IORT cone system. FLASH radiotherapy (FLASH-RT) involves the treatment of tumours at ultra-high dose rates and the IORT cone system can also be used. This study validates the Monte Carlo-based calculations for these small electron beams to accurately determine the dose characteristics of each possible cone-energy combination as well as custom-built alloy cutouts attached to the end of the IORT cone. This will contribute to accurate dose distribution and output factor calculations that are essential to all radiation therapy treatments. A Monte Carlo (MC) model was modelled for electron beams produced by a Siemens Primus LINAC and the IORT cones. The accelerator was built with the component modules available in the BEAMnrc code. The phase-space file generated by the BEAM simulation was used as the source input for the subsequent DOSXYZnrc simulations. Percentage Depth Dose (PDD) data and profiles were extracted from the dose distributions obtained with the DOSXYZnrc simulations. These beam characteristics were compared with measured data for 6, 12, and 18 MeV electron beams for the IORT open cones of diameters 19, 45, and 64 mm and irregularly shaped cutouts. The MC simulations could replicate electron beams within a criterion of 3%/3 mm. Applicator factors were within 0.7%, and cone factors showed good agreement, except for the 9 mm cone size.Based on the successful comparisons between measurement and MC-calculated dose distributions, output factors for the open cones and for small irregularly shaped IORT beams, it may be concluded that the Monte Carlo based dose calculation could replicate electron beams used for IORT and FLASH-IORT.

Design study for a 500 MeV positron beam at the Mainz Microtron MAMI

A design study has been performed for a positron beam with an energy of 500 MeV to be realized at the applied physics area of the Mainz Microtron MAMI. Positrons will be created after pair conversion of bremsstrahlung, produced by the 855 MeV electron beam at MAMI in a tungsten converter target. From the two conceivable geometries (1) pair conversion in the bremsstrahlung converter target itself, and (2) bremsstrahlung pair conversion in a separated lead foil, the former was considered in detail. Positrons will be energy selected within an outside open electron beam-line bending magnet, and bent back by an additional sector magnet. Magnetic focusing elements in between are designed to prepare in a well shielded positron target chamber about 6 m away from the target a beam with horizontal and vertical emittances of epsilon _mathrm{v} = 0.055 pi mm mrad (1 sigma ), and epsilon _mathrm{h} = 0.12, pi mm mrad (1 sigma ), respectively, for a 10 upmu m thick amorphous tungsten target and negligible momentum spread. At an accepted positron band width of 1 MeV, spots are expected vertically with an angular spread of 0.064 mrad and a size of 5.0 mm (FWHM), and horizontally with an angular spread of 0.64 mrad and a size of 7.7 mm (FWHM). The positron yield amounts to 13.1 per second, 1 MeV positron energy band width, and 1 nA electron beam current.Graphic abstract

Femtosecond diagnostics of ultrashort electron beam using a pinhole-based THz-driven deflector

THz-driven resonant structures such as rectangular slits has been widely used for femtosecond temporal characterization of ultrashort electron beams produced in photocathode rf guns. In this work, we show that a simple non-resonant subwavelength pinhole perforated on a metal foil can also provide femtosecond temporal diagnostics to ultrashort electron beams. The streaking effect of the pinhole structure is dominated by the reflected THz field near the surface. A time resolution of 1.5 fs is achieved for a 3 MeV electron beam using a pinhole with diameter of 100 μm. A secondary beam, common in photocathode rf gun but hard to observe with conventional beam diagnostic methods, is also observed with the THz pinhole deflector. In addition to measuring the temporal information of the electron beam, we show that the pinhole may also be used to measure the properties of the THz pulse using the electron beam as the probe. We believe such simple and commercially available pinhole structure is a robust and viable method for femtosecond temporal diagnostics of ultrashort electron beams.

Comparable Long-Term Tumor Control for Hypofractionated FLASH Versus Conventional Radiation Therapy in an Immunocompetent Rat Glioma Model

PurposeTo ensure a clinical translation of FLASH radiation therapy (FLASH-RT) for a specific tumor type, studies on tumor control and toxicity within the same biological system are needed. In this study, our objective was to evaluate tumor control and toxicity for hypofractionated FLASH-RT and conventional radiation therapy (CONV-RT) in an immunocompetent rat glioma model. Methods and MaterialsFisher 344 rats (N = 68) were inoculated subcutaneously with NS1 glioma cells and randomized into groups (n = 9-10 per group). CONV-RT (∼8 Gy/min) or FLASH-RT (70-90 Gy/s) was administered in 3 fractions of either 8 Gy, 12.5 Gy, or 15 Gy using a 10-MeV electron beam. The maximum tumor diameter was measured weekly, and overall survival was determined until day 100. Long-term tumor control was defined as no evident tumor on day 100. Animals were evaluated for acute dermal side effects at 2 to 5 weeks after completed RT and for late dermal side effects at 3 months after initiation of treatment. ResultsSurvival was significantly increased in all irradiated groups compared with control animals (P < .001). In general, irradiated tumors started to shrink at 1 week post–completed RT. In 40% (23 of 58) of the irradiated animals, long-term tumor control was achieved. Radiation-induced skin toxic effects were mild and consisted of hair loss, erythema, and dry desquamation. No severe toxic effect was observed. There was no significant difference between FLASH-RT and CONV-RT in overall survival, acute side effects, or late side effects for any of the dose levels. ConclusionsThis study shows that hypofractionated FLASH-RT results in long-term tumor control rates similar to those of CONV-RT for the treatment of large subcutaneous glioblastomas in immunocompetent rats. Neither treatment technique induced severe skin toxic effects. Consequently, no significant difference in toxicity could be resolved, suggesting that higher doses may be required to detect a FLASH sparing of skin.

Dosimetric characteristics of fabricated germanium doped optical fibres for a postal audit of therapy electron beams

The dosimetric characteristics of germanium (Ge) doped optical fibres are investigated as a potential dosimetric alternative for electron beam therapy postal audits. The dosimetric characteristics of 6 mol% Ge-doped optical fibres fabricated as cylindrical fibres (CF) and flat fibres (FF) are established in terms of signal fading, linearity of dose-response, beam energy- and dose rate dependence. Pilot electron beam therapy audit study irradiations are made with a linear accelerator located at the Royal Surrey County Hospital, applying International Atomic Energy Agency (IAEA) standard irradiation procedures for reference and non-reference conditions. Results for the CF and FF show fading of 26% and 20% respectively at 120 days post-irradiation. For a 6 MeV electron beam the dose-response is observed to be linear over the dose range 1–3 Gy, the least determination coefficient, R2, being 0.985. The results of the electron beam therapy audit are within the tolerance limit of 5% recommended by the International Commission on Radiation Units and Measurements (ICRU) Report No. 24, with a maximum deviation of 4% for FF at a 6 MeV electron beam under non-reference conditions. In conclusion, the fabricated Ge-doped optical fibres are seen to offer suitability for use as an alternative dosimeter to TLD-100 in electron beam therapy postal audit.

Influence of 8 MeV Electron Irradiation on the Properties of ZnO Nanocrystalline Thin Films for Optoelectronic Devices in the High Radiation Environment

Herein, we present the influence of 8 MeV electron beam irradiation on the structural, optical and electrical properties of sol-gel derived spin-coated ZnO films. The electron irradiation doses varied from 0 kGy to 10 kGy. We observed significant changes in the morphology, optical and electrical properties of the films upon irradiation. Structural analysis of the films revealed the preferential and dominant c-axis orientation of the crystallites along the (002) plane. The preferential growth of the films was also supported by the values of texture coefficient. Atomic Force Microscopy studies reveal the linear relationship between the surface roughness, grain size and irradiation dose. The average transmittance of the films decreased from 87% to 66% after irradiation. A slight red-shift of the optical band gap values was observed when the absorbed dose was increased from 0 kGy to 10 kGy. The Photoluminescence measurement of the films showed that the intensity of the defect-related peak increases with the electron dose. The electrical resistivity of the films decreased after irradiation and a minimum resistivity of 7.566 × 10−2 Ω m was obtained from the film irradiated with a 5 kGy electron dose. To find the performance and quality of the prepared film, the Figure of Merit was calculated and was found that the film irradiated with a 5 kGy electron dose shows the maximum value. The obtained results show that electron irradiation is a potential alternative approach to improve the performance of the ZnO films for optoelectronic devices in a high radiation environment.

Influence of PEG-coated Bismuth Oxide Nanoparticles on ROS Generation by Electron Beam Radiotherapy

Abstract Introduction: Nanoparticles (NPs) have been proven to enhance radiotherapy doses as radiosensitizers. The introduction of coating materials such as polyethylene glycol (PEG) to NPs could impact the NPs’ biocompatibility and their effectiveness as radiosensitizers. Optimization of surface coating is a crucial element to ensure the successful application of NPs as a radiosensitizer in radiotherapy. This study aims to investigate the influence of bismuth oxide NPs (BiONPs) coated with PEG on reactive oxygen species (ROS) generation on HeLa cervical cancer cell line. Material and methods: Different PEG concentrations (0.05, 0.10, 0.15 and 0.20 mM) were used in the synthesis of the NPs. The treated cells were irradiated with 6 and 12 MeV electron beams with a delivered dose of 3 Gy. The reactive oxygen species (ROS) generation was measured immediately after and 3 hours after irradiation. Results: The intracellular ROS generation was found to be slightly influenced by electron beam energy and independent of the PEG concentrations. Linear increments of ROS percentages over the 3 hours of incubation time were observed. Conclusions: Finally, the PEG coating might not substantially affect the ROS generated and thus emphasizing the functionalized BiONPs application as the radiosensitizer for electron beam therapy.

Dosimetric considerations for moldable silicone composites used in radiotherapy applications.

Due to their many favorable characteristics, moldable silicone (MS) composites have gained popularity in medicine and recently, in radiotherapy applications. We investigate the dosimetric properties of silicones in radiotherapy beams and determine their suitability as water substitutes for constructing boluses and phantoms. Two types of silicones were assessed (ρ= 1.04 g/cm3 and ρ= 1.07 g/cm3). Various dosimetric properties were characterized, including the relative electron density, the relative mean mass energy‐absorption coefficient, and the relative mean mass restricted stopping power. Silicone slabs with thickness of 1.5 cm and 5.0 cm were molded to mimic a bolus setup and a phantom setup, respectively. Measurements were conducted for Co‐60 and 6 MV photon beams, and 6 MeV electron beams. The doses at 1.5 cm and 5.0 cm depths in MS were measured with solid water (SW) backscatter material (D MS–SW), and with a full MS setup (D MS–MS), then compared with doses at the same depths in a full SW setup (D SW–SW). Relative doses were reported as D MS–SW/D MS–SW and D MS–MS/D SW–SW. Experimental results were verified using Monaco treatment planning system dose calculations and Monte Carlo EGSnrc simulations. Film measurements showed varying dose ratios according to MS and beam types. For photon beams, the bolus setup D MS–SW/D SW–SW exhibited a 5% relative dose reduction. The dose for 6 MV beams was reduced by nearly 2% in a full MS setup. Up to 2% dose increase in both scenarios was observed for electron beams. Compared with dose in SW, an interface of MS–SW can cause relatively high differences. We conclude that it is important to characterize a particular silicone's properties in a given beam quality prior to clinical use. Because silicone compositions vary between manufacturers and differ from water/SW, accurate dosimetry using these materials requires consideration of the reported differences.

Optical Response of Expired EBT3 Film for Absorbed Dose Measurement in X-ray and Electron Beam Range

The purpose of this study was to investigate the optical response of an expired External Beam Therapy (EBT3) film, which expired in 2018, using X-rays and electron beam doses. The film’s optical responses were evaluated for its usability in measuring different radiation sources, energy, and absorbed doses ranging up to 5 Gy. Pieces of the expired EBT3 film were irradiated with 90 kVp, 6 MV X-ray photons, and 6 MeV electron beam. The analysis was performed using the Jaz visible spectrometer and EPSON Perfection V370 Photo scanner to obtain the absorbance and the net relative optical density (ROD) of the film samples respectively. The results showed that spectroscopic measurements of the exposed expired EBT3 films under these radiation sources were able to produce primary secondary peaks at λ = 633.52 nm and λ = 582.3 nm respectively. The best wavelength subsets that presented the best MLR regression fitting for all experiments were 541.48 nm, 561.11 nm, and 600.28 nm. While, for the 6 MV photon and the 6 MeV electron beam they were 600.28 nm, 650.79 nm and 654.10 nm. In case of the irradiation with the 6 MV photon and the 6 MeV electron beam, expired EBT3 film showed no significant differences, which made it suitable for dosimetry in various sources of radiation. The individual calibration of radiation dose produces very high measurement accuracy with coefficient of determination, R2 above 0.99 and root mean square of error, RMSE of 0.038 Gy, 0.113 Gy, and 0.115 Gy for films irradiated with 90 kVp X-rays, 6 MV photon beam, and 6 MeV electron beam respectively. Hence, from the results, the expired EBT3 film used in this study showed promising usability of expired EBT3 films beyond their prescribed expiry dates.

Characterization of the PTB ultra-high pulse dose rate reference electron beam

Purpose. This investigation aims to present the characterisation and optimisation of an ultra-high pulse dose rate (UHPDR) electron beam at the PTB facility in Germany. A Monte Carlo beam model has been developed for dosimetry study for future investigation in FLASH radiotherapy and will be presented. Material and methods. The 20 MeV electron beams generated by the research linear accelerator has been characterised both in-beamline with profile monitors and magnet spectrometer, and in-water with a diamond detector prototype. The Monte Carlo model has been used to investigate six different setups to enable different dose per pulse (DPP) ranges and beam sizes in water. The properties of the electron radiation field in water have also been characterised in terms of beam size, quality specifier R 50 and flatness. The beam stability has also been studied. Results. The difference between the Monte-Carlo simulated and measured R 50 was smaller than 0.5 mm. The simulated beam sizes agreed with the measured ones within 2 mm. Two suitable setups have been identified for delivering reference UHPDR electron beams. The first one is characterised by a SSD of 70 cm, while in the second one an SSD of 90 cm is used in combination with a 2 mm aluminium scattering plates. The two set-ups are quick and simple to install and enable an expected overall DPP range from 0.13 Gy up to 6.7 Gy per pulse. Conclusion. The electron beams generated by the PTB research accelerator have shown to be stable throughout the four-months length of this investigation. The Monte Carlo models have shown to be in good agreement for beam size and depth dose and within 1% for the beam flatness. The diamond detector prototype has shown to be a promising tool to be used for relative measurements in UHPDR electron beams.