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Journal of Radiological Protection :... Sep 2023Here we investigate the annual effective dose rate obtained from gamma radiation emitted from radionuclides in construction materials in a model room with fixed...
Here we investigate the annual effective dose rate obtained from gamma radiation emitted from radionuclides in construction materials in a model room with fixed dimensions. The dose rate is calculated on the whole room area at half the room height. We focus our analyses on a comparison of the annual effective dose rate between the room centre and the room average at half the room height and provide wall-wise quadratic index equations for both. We find that the annual effective dose rate based on the room average is larger than for the room centre due to increased annual effective dose rates for positions in the room closer to the walls. Furthermore, we evaluate the annual effective dose rate under a non-equal distribution of radionuclides in the three wall types (floor and ceiling, long walls, short walls). When considering the room average of the annual effective dose rate, our analysis indicates that it appears advantageous to use construction materials with a higher radionuclide activity concentration for floor and ceiling and the material with a lower radionuclide content for long and short walls, if there is a choice in the construction process.
Topics: Construction Materials; Gamma Rays; Radioisotopes
PubMed: 37647869
DOI: 10.1088/1361-6498/acf505 -
Physica Medica : PM : An International... Feb 2023In the current study, the energy and dose rate dependence of a new genipin-based gel dosimeter, named GENA gel dosimeter, were investigated.
PURPOSE
In the current study, the energy and dose rate dependence of a new genipin-based gel dosimeter, named GENA gel dosimeter, were investigated.
METHODS
Prepared gel dosimeters exposed using a Varian clinical linac. Beam qualities of 6 and 18 MV were applied to investigate the GENA gel dosimeter's energy dependence. Furthermore, the gel dosimeters were exposed to 50, 100, 200, and 350 cGy/min dose rates, ranging from 0 to 8 Gy. The irradiated gel dosimeters were read out using a double beam UV-Visible spectrophotometer. The absorbance peak (AP) and area under spectrum (AUS) were evaluated.
RESULTS
Absorbance-dose sensitivities of (8.0 ± 0.18) × 10 cmGy and (7.8 ± 0.15) × 10 cmGy were obtained for GENA gel dosimeter for 6 and 18 MV beam qualities, respectively. Results specified no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities irradiated using the two energies mentioned above. For the mentioned dose rates, AP-dose sensitivities of (8.2 ± 0.22) × 10, (8.1 ± 0.21) × 10, (8.1 ± 0.2) × 10 and (8.0 ± 0.18) × 10 cmGy were obtained, respectively. Results showed no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities for the investigated dose rates and energies. In addition, results revealed that when the incident photon energy and dose rate changed, there were no significant differences (p > 0.05) between the GENA gel dosimeter's dose resolution values.
CONCLUSIONS
It is concluded that the response of the GENA gel dosimeter is not dependent on the energy and dose rate (p > 0.05) within the studied energy and dose rate ranges.
Topics: Radiation Dosimeters; Photons; Radiometry
PubMed: 36603480
DOI: 10.1016/j.ejmp.2022.102522 -
Bulletin Du Cancer Apr 2017In this review, we present the synthesis of the newly acquired knowledge concerning high dose-rate irradiations and the hopes that these new radiotherapy modalities give... (Review)
Review
In this review, we present the synthesis of the newly acquired knowledge concerning high dose-rate irradiations and the hopes that these new radiotherapy modalities give rise to. The results were presented at a recent symposium on the subject.
Topics: Animals; Electrons; Humans; Mice; Neoplasms; Proton Therapy; Radiotherapy; Radiotherapy Dosage
PubMed: 28283183
DOI: 10.1016/j.bulcan.2017.01.012 -
Physics in Medicine and Biology Aug 2023. The objective of this study was to investigate the impact of mean and instantaneous dose rates on the production of reactive oxygen species (ROS) during ultra-high...
. The objective of this study was to investigate the impact of mean and instantaneous dose rates on the production of reactive oxygen species (ROS) during ultra-high dose rate (UHDR) radiotherapy. The study aimed to determine whether either dose rate type plays a role in driving the FLASH effect, a phenomenon where UHDR radiotherapy reduces damage to normal tissues while maintaining tumor control.. Assays of hydrogen peroxide (HO) production and oxygen consumption (ΔpO) were conducted using UHDR electron irradiation. Aqueous solutions of 4% albumin were utilized as the experimental medium. The study compared the effects of varying mean dose rates and instantaneous dose rates on ROS yields. Instantaneous dose rate was varied by changing the source-to-surface distance (SSD), resulting in instantaneous dose rates ranging from 10to 10Gy s. Mean dose rate was manipulated by altering the pulse frequency of the linear accelerator (linac) and by changing the SSD, ranging from 0.14 to 1500 Gy s.. The study found that both ΔHOand ΔpOdecreased as the mean dose rate increased. Multivariate analysis indicated that instantaneous dose rates also contributed to this effect. The variation in ΔpOwas dependent on the initial oxygen concentration in the solution. Based on the analysis of dose rate variation, the study estimated that 7.51 moles of HOwere produced for every mole of Oconsumed.. The results highlight the significance of mean dose rate as a predictor of ROS production during UHDR radiotherapy. As the mean dose rate increased, there was a decrease in oxygen consumption and in HOproduction. These findings have implications for understanding the FLASH effect and its potential optimization. The study sheds light on the role of dose rate parameters and their impact on radiochemical outcomes, contributing to the advancement of UHDR radiotherapy techniques.
Topics: Reactive Oxygen Species; Electrons; Hydrogen Peroxide; Oxygen; Heart Rate; Radiotherapy Dosage
PubMed: 37463588
DOI: 10.1088/1361-6560/ace877 -
Scientific Reports Dec 2022The Radiological Research Accelerator Facility has modified a decommissioned Varian Clinac to deliver ultra-high dose rates: operating in 9 MeV electron mode (FLASH...
The Radiological Research Accelerator Facility has modified a decommissioned Varian Clinac to deliver ultra-high dose rates: operating in 9 MeV electron mode (FLASH mode), samples can be irradiated at a Source-Surface Distance (SSD) of 20 cm at average dose rates of up to 600 Gy/s (3.3 Gy per 0.13 µs pulse, 180 pulses per second). In this mode multiple pulses are required for most irradiations. By modulating pulse repetition rate and irradiating at SSD = 171 cm, dose rates below 1 Gy/min can be achieved, allowing comparison of FLASH and conventional irradiations with the same beam. Operating in 6 MV photon mode, with the conversion target removed (SuperFLASH mode), samples are irradiated at higher dose rates (0.2-150 Gy per 5 µs pulse, 360 pulses per second) and most irradiations can be performed with a single very high dose rate pulse. In both modes we have seen the expected inverse relation between dose rate and irradiated area, with the highest dose rates obtained for beams with a FWHM of about 2 cm and ± 10% uniformity over 1 cm diameter. As an example of operation of the ultra-high dose rate FLASH irradiator, we present dose rate dependence of dicentric chromosome yields.
Topics: Particle Accelerators; Photons; Electrons; Radiotherapy Dosage; Radiometry
PubMed: 36550150
DOI: 10.1038/s41598-022-19211-7 -
Genome Integrity 2019Nontargeted effects include radiation-induced genomic instability (RIGI) which is observed in the progeny of cells exposed to ionizing radiation and can be manifested in...
Nontargeted effects include radiation-induced genomic instability (RIGI) which is observed in the progeny of cells exposed to ionizing radiation and can be manifested in different ways, including chromosomal instability and micronucleus (MN) formation. Since genomic instability is commonly observed in tumors and has a role in tumor progression, RIGI has the potential of being an important mechanism for radiation-induced cancer. The work presented explores the role of dose and dose rate on RIGI, determined using a MN assay, in normal primary human fibroblast (HF19) cells exposed to either 0.1 Gy or 1 Gy of X-rays delivered either as an acute (0.42 Gy/min) or protracted (0.0031 Gy/min) exposure. While the expected increase in MN was observed following the first mitosis of the irradiated cells compared to unirradiated controls, the results also demonstrate a significant increase in MN yields in the progeny of these cells at 10 and 20 population doublings following irradiation. Minimal difference was observed between the two doses used (0.1 and 1 Gy) and the dose rates (acute and protracted). Therefore, these nontargeted effects have the potential to be important for the low-dose and dose-rate exposure. The results also show an enhancement of the cellular levels of reactive oxygen species after 20 population doublings, which suggests that ionising radiation (IR) could potentially perturb the homeostasis of oxidative stress and so modify the background rate of endogenous DNA damage induction. In conclusion, the investigations have demonstrated that normal primary human fibroblast (HF19) cells are susceptible to the induction of early DNA damage and RIGI, not only after a high dose and high dose rate exposure to low linear energy transfer, but also following low dose, low dose rate exposures. The results suggest that the mechanism of radiation induced RIGI in HF19 cells can be correlated with the induction of reactive oxygen species levels following exposure to 0.1 and 1 Gy low-dose rate and high-dose rate x-ray irradiation.
PubMed: 31897286
DOI: 10.4103/genint.genint_5_19 -
Radiation and Environmental Biophysics Nov 2017External dose coefficients for environmental exposure scenarios are often computed using assumption on infinite or semi-infinite radiation sources. For example, in the...
External dose coefficients for environmental exposure scenarios are often computed using assumption on infinite or semi-infinite radiation sources. For example, in the case of a person standing on contaminated ground, the source is assumed to be distributed at a given depth (or between various depths) and extending outwards to an essentially infinite distance. In the case of exposure to contaminated air, the person is modeled as standing within a cloud of infinite, or semi-infinite, source distribution. However, these scenarios do not mimic common workplace environments where scatter off walls and ceilings may significantly alter the energy spectrum and dose coefficients. In this paper, dose rate coefficients were calculated using the International Commission on Radiological Protection (ICRP) reference voxel phantoms positioned in rooms of three sizes representing an office, laboratory, and warehouse. For each room size calculations using the reference phantoms were performed for photons, electrons, and positrons as the source particles to derive mono-energetic dose rate coefficients. Since the voxel phantoms lack the resolution to perform dose calculations at the sensitive depth for the skin, a mathematical phantom was developed and calculations were performed in each room size with the three source particle types. Coefficients for the noble gas radionuclides of ICRP Publication 107 (e.g., Ne, Ar, Kr, Xe, and Rn) were generated by folding the corresponding photon, electron, and positron emissions over the mono-energetic dose rate coefficients. Results indicate that the smaller room sizes have a significant impact on the dose rate per unit air concentration compared to the semi-infinite cloud case. For example, for Kr-85 the warehouse dose rate coefficient is 7% higher than the office dose rate coefficient while it is 71% higher for Xe-133.
Topics: Humans; Immersion; Male; Occupational Exposure; Phantoms, Imaging; Radiation Dosage; Reference Standards; Skin
PubMed: 28840329
DOI: 10.1007/s00411-017-0705-6 -
International Journal of Radiation... 2023Increasing epidemiological and biological evidence suggests that radiation exposure enhances cancer risk in a dose-dependent manner. This can be attributed to the... (Review)
Review
PURPOSE
Increasing epidemiological and biological evidence suggests that radiation exposure enhances cancer risk in a dose-dependent manner. This can be attributed to the 'dose-rate effect,' where the biological effect of low dose-rate radiation is lower than that of the same dose at a high dose-rate. This effect has been reported in epidemiological studies and experimental biology, although the underlying biological mechanisms are not completely understood. In this review, we aim to propose a suitable model for radiation carcinogenesis based on the dose-rate effect in tissue stem cells.
METHODS
We surveyed and summarized the latest studies on the mechanisms of carcinogenesis. Next, we summarized the radiosensitivity of intestinal stem cells and the role of dose-rate in the modulation of stem-cell dynamics after irradiation.
RESULTS
Consistently, driver mutations can be detected in most cancers from past to present, supporting the hypothesis that cancer progression is initiated by the accumulation of driver mutations. Recent reports demonstrated that driver mutations can be observed even in normal tissues, which suggests that the accumulation of mutations is a necessary condition for cancer progression. In addition, driver mutations in tissue stem cells can cause tumors, whereas they are not sufficient when they occur in non-stem cells. For non-stem cells, tissue remodeling induced by marked inflammation after the loss of tissue cells is important in addition to the accumulation of mutations. Therefore, the mechanism of carcinogenesis differs according to the cell type and magnitude of stress. In addition, our results indicated that non-irradiated stem cells tend to be eliminated from three-dimensional cultures of intestinal stem cells (organoids) composed of irradiated and non-irradiated stem cells, supporting the stem-cell competition.
CONCLUSIONS
We propose a unique scheme in which the dose-rate dependent response of intestinal stem cells incorporates the concept of the threshold of stem-cell competition and context-dependent target shift from stem cells to whole tissue. The concept highlights four key issues that should be considered in radiation carcinogenesis: i.e. accumulation of mutations; tissue reconstitution; stem-cell competition; and environmental factors like epigenetic modifications.
Topics: Humans; Dose-Response Relationship, Radiation; Carcinogenesis; Stem Cells; Radiation Exposure; Mutation
PubMed: 36971595
DOI: 10.1080/09553002.2023.2194398 -
Journal of Radiation Research Mar 2023While epidemiological data are available for the dose and dose-rate effectiveness factor (DDREF) for human populations, animal models have contributed significantly to... (Review)
Review
While epidemiological data are available for the dose and dose-rate effectiveness factor (DDREF) for human populations, animal models have contributed significantly to providing quantitative data with mechanistic insights. The aim of the current review is to compile both the in vitro experiments with reference to the dose-rate effects of DNA damage and repair, and the animal studies, specific to rodents, with reference to the dose-rate effects of cancer development. In particular, the review focuses especially on the results pertaining to underlying biological mechanisms and discusses their possible involvement in the process of radiation-induced carcinogenesis. Because the concept of adverse outcome pathway (AOP) together with the key events has been considered as a clue to estimate radiation risks at low doses and low dose-rates, the review scrutinized the dose-rate dependency of the key events related to carcinogenesis, which enables us to unify the underlying critical mechanisms to establish a connection between animal experimental studies with human epidemiological studies.
Topics: Animals; Humans; Dose-Response Relationship, Radiation; Neoplasms, Radiation-Induced; Mammary Glands, Human; Risk Assessment; Radiation Exposure; Carcinogenesis; Models, Animal; Gastrointestinal Tract
PubMed: 36773323
DOI: 10.1093/jrr/rrad002 -
Ophthalmology Science 2024To describe a pilot study on the use of single-session, high-dose-rate, Food and Drug Administration-cleared, yttrium-90 (Y) plaque brachytherapy for iris and...
PURPOSE
To describe a pilot study on the use of single-session, high-dose-rate, Food and Drug Administration-cleared, yttrium-90 (Y) plaque brachytherapy for iris and iridociliary melanoma.
DESIGN
A single-center, clinical case series.
PARTICIPANTS
Six consecutive patients were included in this study. Each was diagnosed with an iris or iridociliary melanoma based on clinical examination with or without biopsy.
METHODS
Each tumor was staged according to the American Joint Committee on Cancer criteria and received Y eye plaque brachytherapy. The main variables were tumor size, patient age, sex, and method of diagnosis (clinical or biopsy). Surgical techniques, treatment durations, and ocular side effects were recorded. Local control was defined as a lack of tumor growth or regression determined by clinical examinations, including slit-lamp and gonio photography, as well as high-frequency ultrasound measurements. Toxicity parameters included acute and short-term corneal/scleral change, anterior segment inflammation, and cataract progression.
MAIN OUTCOME MEASURES
Local and systemic cancer control, tumor regression, visual acuity, as well as radiation-related normal tissue toxicity.
RESULTS
High-dose-rate Y plaque brachytherapy was used to treat small (American Joint Committee on Cancer cT1) category melanomas. Single-surgery high-dose-rate irradiations were performed under anesthesia. Because of short treatment durations, high-dose-rate Y did not require the additional procedures used for low-dose-rate plaque (e.g., sutures, amniotic membrane epicorneal buffering, Gunderson flaps, and second surgeries for plaque removal). Only conjunctival recession was used to avoid normal tissue irradiation. High-dose-rate Y treatment durations averaged 8.8 minutes (median, 7.9; range, 5.8-12.9). High-dose-rate Y brachytherapy was associated with no periorbital, corneal (Descemet folds), or conjunctival edema. There was no acute or short-term anterior uveitis, secondary cataract, scleropathy, radiation retinopathy, maculopathy, or optic neuropathy. The follow-up was a mean of 16.0 (range 12-24) months. Evidence of local control included a lack of expansion of tumor borders ( = 6, 100%), darkening with or without atrophy of the tumor surface ( = 5/6, 83%), and a mean 24.5% reduction in ultrasonographically measured tumor thickness. There were no cases of metastatic disease.
CONCLUSIONS
High-dose-rate Y brachytherapy allowed for single-surgery, minimally invasive, outpatient irradiation of iris and iridociliary melanomas.
FINANCIAL DISCLOSURES
Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
PubMed: 38840779
DOI: 10.1016/j.xops.2024.100513