Radiation Measurements最新文献

A study on retrospective dosimetry was performed using electronic personal dosimeters (EPDs) for reconstructing doses received by radiographic testing workers. The dosimetric properties of the thermoluminescence (TL) peak in the temperature range of 100–200 °C were investigated by measuring the TL of the resistors extracted from the EPDs in a darkroom environment. Results showed that this TL peak exhibited optimal dosimetric properties, with a minimum detectable dose as low as 13 mGy. To calculate the absorbed dose using the resistors, a simplified single aliquot regenerative (SAR) dose method using the TL peak was employed. The zero dose of the commercial EPD (model CLOVER) was determined to be 58 ± 72 mGy through the random selection of six EPDs. Additionally, a dose overestimation correction factor for compensating rapid sensitivity changes after TL measurement of the natural sample was calculated as 1.73 ± 0.09. Furthermore, it was observed that the TL signal faded exponentially to approximately 60% over a period of 12 weeks. Subsequently, retrospective dosimetry was performed by irradiating EPDs with a standard gamma ray dose of 1 Gy. The radiation exposure dose calculated from the TL peak of the resistors was found to be approximately 10% lower. These findings showed that the retrospective dosimetry with EPD can be utilized for accurately estimating the radiation exposure dose.

This study investigates the potential use of dietary supplements and pharmaceuticals containing magnesium, calcium or potassium for emergency dosimetry applications using the phenomenon of optically stimulated luminescence (OSL). Signal measurements were carried out using different stimulation wavelengths, and blue light stimulation was found to be the most efficient. More than half of the samples exhibited a measurable OSL signal and relatively high radiation sensitivity compared to other previously measured emergency detectors. Moreover, samples generally demonstrated a linear dose response. Possible causes of their high zero-dose signal were investigated: mechanical processing and UV light excitation. As variability in sensitivity was observed, the test-dose protocol was used during measurements. Furthermore, the study showed a significant loss of OSL signal intensity within 24 h after irradiation, which suggests the necessity for a fading correction. Finally, a dose recovery test was performed to evaluate the materials and the test-dose protocol under realistic conditions. The findings indicate the potential for using pharmaceuticals and dietary supplements in the event of a radiation emergency due to their dosimetric properties and ease of obtaining.

Background and purpose

The investigation of the FLASH effect requires experimental accelerators capable of delivering ultra-high dose rate (UHDR) beams. Rapid widespread use of this technology could be achieved by modifying clinical electron linacs, originally designed to deliver megavoltage photon radiation up to a few Gy per minute to the isocenter, to deliver electron beams at 40 Gy/s and beyond. Only limited experience has been reported on the radiation safety of UHDR electron beams. This work aims to evaluate the performance and applicability of radiation detectors to quantitatively assess the radiation exposure in this context.

Methods

A Varian TrueBeam linac has been modified to deliver 16-MeV electron UHDR with dose rates up to 3⋅10⁵ Gy/s (instantaneous) and 256 Gy/s (average) at the isocenter and used to investigate the detectors performances. A short-term survey was performed at the first UHDR beam-on with passive and active detectors. Then, a long-term survey was conducted with passive detectors during the first three months of operation of the UHDR linac. Moreover, linearity of detector response, activation of the linac components and secondary radiation inside the bunker were evaluated.

Results

Selected active survey metres were shown to have a linear response for the detection of the ambient radiation outside the bunker when performing pulsed UHDR irradiations. The most critical locations outside the bunker were identified at the bunker door and at the control room. The results showed that the operation of the linac with a workload limit of 1000 Gy/week at the isocenter would allow respecting a limit of 0.02 mSv/week to the personnel. The activation of the linac head with 16-MeV electron beam was more than ten times greater with conventional beams compared to UHDR. The secondary radiation inside the bunker was also reduced by −27% when employing UHDR beams.

Conclusions

This work provides a comprehensive evaluation of the suitability of active and passive detectors to perform a radiation safety assessment for a 16-MeV electron UHDR linac. The conditions under which commonly available survey metres for photons (FLUKE 451P) and neutrons (Ludlum Model 3007) can safely be employed in controlled areas outside the bunker were investigated. Moreover, we showed that if a radiation vault is safe for 16-MeV electron beams at conventional dose rates, this applies also to UHDR when fixing the linac weekly workload to a given amount of dose at the isocenter.

The Paul Scherrer Institute is a unique Swiss research institute that operates five large-scale research facilities in which different types of particles, such as electrons, protons, neutrons, pions and muons, are accelerated or produced. Depending on the facility and location, the operational radiation protection has to deal with challenging measurements of mixed radiation fields, which can be in addition pulsed and of high-energy. In this article, we provide insight into the associated demands and challenges using two examples with different requirements for the monitoring technology. Using the example of the high-intensity proton accelerator (HIPA), the measurement technology around high-energy accelerators is examined in more detail. On the other hand, the problems of measuring technology for pulsed radiation and its dynamic range are discussed using the example of the Swiss X-ray free electron laser SwissFEL. The aim of this paper is to highlight the different requirements and technical challenges in radiation measurements for such complex facilities and, thus, to raise awareness and provide a stimulus for further developments in measurement technology.

- This paper aims to enhance our understanding of the effects of ionizing radiation using radiobiology and biodosimetry techniques applied to living plant organisms. Plants are particularly suitable for this purpose as they are highly sensitive to detecting potential genotoxic agents in the environment and their use allows us to avoid using animals in research in compliance with the 3R principle. Currently, the onion (Allium cepa) is recognized as a valid model for the analysis of environmental pollutants but has been relatively unexplored as an indicator of radiation exposure. In this study, analyses of the genotoxicity of X and alpha radiation were conducted using the micronucleus test and mitotic index analysis. Our results indicate that Allium cepa can be considered a valid alternative model to animal use for assessing the effects of ionizing radiation. In particular, it was found that alpha radiation caused significant damage, as evidenced by an increased number of micronuclei, which was 20 times higher compared to X-ray radiation. This was further confirmed through the observation of the effective dose parameter, as determined by the analysis of various weight factors associated with different types of radiation.

In radiobiology, studies on the irradiation of neoplastic cells in vitro are crucial for advancing treatment knowledge, specifically in neoplastic cells. These investigations aim to discover optimal doses, dose fractionation approaches, and potential concurrent treatment modalities to enhance damage to neoplastic cells. An experimental setup for cell culture irradiation was proposed with a focus on controlling the beam's build-up region and lateral and backscatter, coupled with an emphasis on the importance of a simple, reproducible, and standardized position. This setup comprises an acrylic plate with 96-well and plates of solid water. Computed tomography images of the setup were acquired in various configurations, these images were used to plan irradiation in the treatment planning system, employing two dose calculation algorithms AcurosXB and AAA, for the 6 MV LINAC with a 20 × 20 cm² field size and 100 cm of source-skin distance (SSD).

Radiochromic films (EBT3) were used to quantify a planned dose of 2 Gy to evaluate experimental dosimetry. Under the same conditions and geometry, the PENELOPE Monte Carlo simulation code was employed to validate the experimentally obtained data. Film dosimetry highlighted dose variations, with an uncertainty of 8 % in reported values, indicating that not all wells need to be filled for satisfactory absorption.

The results of simulations using the PENELOPE code validated the stability of our setup, emphasizing the importance of control in the build-up region and scattering factors. The experimental configuration allowed for obtaining a uniform dose distribution throughout the cell culture, even in the absence of a cell culture medium within each well of the culture plate.

Radiophotoluminescence (RPL) has been a key phenomenon in dosimetry. Most materials exhibiting RPL are inorganic single crystals, glasses, and ceramics. Recently, similar phenomena (i.e., fluorescence after irradiation) have been realized in soft matters, such as liquids, gels, and organic solids, on the basis of the radiation-induced production of fluorescent molecules. Dosimeters showing such phenomena are attractive from the viewpoints of their tissue equivalence, flexibility, scalability, and workability. The objective of this paper is to present an overview of such dosimeters with emphasis on the radiation chemical reactions used in the materials. Moreover, the sensitivity and the measurable range is introduced.

A constant value of the Relative Biological Effectiveness ($RBE$), equal to 1.1, to weight the physical dose of proton therapy treatment planning collides with the experimental evidence of an increase of effectiveness along the depth dose profile, especially at the end of the particle range. In this context, it is desirable to develop new optimized treatment planning systems that account for a variable RBE when weighting the physical dose. In particular, due to the increasing interest on microdosimetry as a possible methodology for measuring physical quantities correlated with the biological effectiveness of the therapeutic beam, the development of new Tissue-Equivalent Proportional Counters (TEPCs) specifically designed for the clinical environment are in progress.

In this framework, the silicon technology allows to produce solid state detectors of real micrometric dimensions. This is a valid alternative to the TEPC from a practical point of view, being simple, easy-of-use and more versatile. The feasibility of a solid state microdosimeter based on a monolithic double stage silicon telescope has been previously proposed and deeply investigated by comparing its response to the one obtained by reference TEPCs in various radiation fields. The device is constituted by a matrix of cylindrical elements, 2 μm in thickness and 9 μm in diameter, coupled to a single E stage, 500 μm in thickness. Each segmented ΔE stage acts as a solid state microdosimeter, while the E stage gives information on the energy of the impinging proton up to about 8 MeV.

This work is dedicated to the description of the microdosimetric characterization of the 148 MeV energy-modulated proton beam at the radiobiological research line of the Trento Proton Therapy Centre by means of a pixelated silicon microdosimeter. All measurements were carried out at different positions across the spread-out Bragg peak (SOBP) and the corresponding microdosimetric distributions were derived by applying a novel extrapolation algorithm. Finally, microdosimetric assessment of Relative Biological Effectiveness was carried out by weighting the dose distribution of the lineal energy with the Loncol's biological weighting function. Benefits and possible limitations of this approach are discussed.

Bone Mineral Density (BMD) can be determined by applying the Digital Image Processing (DIP) method using medical X-ray diagnosis. Although only the second metacarpal bone is analyzed in this approach, other parts of the body are exposed to X-ray radiation. We here propose a novel procedure in which parts of the hand surrounding the area of interest are shielded with an X-ray shielding sheet having low shielding performance. In our procedure, the main diagnostic area is not shielded, and other areas are covered with an X-ray shielding sheet with a low shielding performance. The sheet was fabricated by embedding Bi₂O₃ particles in resin sheet. We assessed the clinical performance of this method using three types of hand phantoms and conventional diagnostic X-ray equipment. The dose reduction for the entire hand region was evaluated by the Dose Area Product (${DAP}_{\text{Hand}}$), which was measured with a small dosimeter, and the hand area was determined from the X-ray image. The X-ray image of the second metacarpal bone is affected by the contribution of X-rays that penetrate the object of interest and are scattered in other areas of the hand. Because our X-ray shielding sheet suppressed the generation of scattered X-rays, the pixel value of the second metacarpal bone and corresponding BMD value are varied. To address this issue, we developed a correction algorithm. We found that the X-ray shields with Dose Reduction Factor ($DRF$) values of 40–60% were appropriate for our methodology. Our method was estimated to have a percentage uncertainty of approximately 5% for the derivation of BMD values. Morphological information of the hand and bones could thus be clearly observed. We verified that both morphological diagnosis and quantitative determination of BMD are possible when DIP procedure is conducted using our shield.

The advantages of proton and light ion beam therapy compared to conventional photon radiation therapy are well-known, mainly thanks to the characteristic depth dose distribution of ions and their radio-biological effectiveness. Nevertheless, the use of ions implies different nuclear reactions that generate secondary particles, with neutrons among them. These secondary neutrons can travel far away from the treatment volume, their measurement is a challenging complex task, and their biological effects are particularly high for neutrons with energies in the MeV range. In this review, a comprehensive description of secondary neutron dosimetry in proton and light ion beam therapy is given. Many studies have been conducted on the quantification of the secondary neutron dose, most of them have been performed for proton beams, whereas for other ions like carbon, the available information is scarce. The main measurement campaigns are summarised, focusing on the type of detectors used. In line with the detectors’ advantages and limitations, measurements performed inside and outside anthropomorphic phantoms are considered. The role of Monte Carlo radiation transport simulations is discussed since many experimental detection techniques need additional simulations to provide dose estimates. A focus on the current challenges for the measurements of neutrons with energies above 20 MeV is given, as this is one of the main components of secondary neutrons produced by therapeutic ion beams. Finally, the potential clinical relevance of the available and needed secondary neutron dose data is discussed, in terms of its impact on the treatment of patients. For this, the relative biological effectiveness of neutrons and the potential risk of cancer induction re-incidence or secondary cancer due to secondary neutron doses play a key role.