This study establishes a robust and clinically applicable calibration protocol for optically stimulated luminescence dosimeters (OSLDs) in diagnostic radiology, with the aim of improving the accuracy of patient dose assessment. A total of 144 OSLDs were systematically irradiated under controlled conditions to assess their dosimetric response across a wide range of tube voltages (40-150 kVp) and square field sizes (10 × 10 cm² to 30 × 30 cm²). The dosimeters exhibited a sensitivity variation of ±6.6%, with an average background dose of 0.0185 mGy. The experimental data revealed a high dependence of OSLD response on photon energy, with dose values increasing by a factor of 11.5, from 0.1393 mGy at 40 kVp to 1.6072 mGy at 150 kVp for a constant field size of 10 × 10 cm². A pronounced non-linear dose escalation was observed in the mid-kVp range (70-100 kVp), where dose measurements increased by 72-90% as field size expanded. Energy and geometry-specific correction factors were derived, showing significant variation with field size, reaching maximum values of 9.81 for the 30 × 30 cm² field at 150 kVp and 7.43 for the 10 × 10 cm² field under the same conditions. Additionally, notable discrepancies were observed between experimentally derived effective beam energies and reference values reported by the International Atomic Energy Agency (IAEA), highlighting the need for localized calibration standards. These findings contribute to the standardization of OSLD calibration protocols in diagnostic radiology and support their implementation for accurate patient dose monitoring in clinical settings.

Hyperthyroidism is a very common endocrine disorder in both humans and cats. Radioactive iodine ablation therapy is the preferred treatment option because of its high success rate; however, the patient becomes a radiation source and poses a potential radiological risk to others. The regulations governing release criteria differ between human medicine and veterinary medicine. A human patient can receive up to 1,200 MBq of 131I and be discharged the same day; yet a cat can receive a dose as low as 74 MBq and require weeks of hospitalization. This discrepancy has not been satisfactorily addressed; and overly restrictive release criteria can place a burden on the veterinary staff, the cat, and the owner. In this study, administered activities and exposure rates are measured for hyperthyroid cats undergoing treatment at Louisiana State University Veterinary Teaching Hospital to determine if current criteria are too restrictive for releasing cats to their owners. Additionally, radioassays are performed on the surface of the cat, its excreta, and its environment to characterize the potential exposures to the cat owners. Annual total effective dose equivalents to the cat owners are calculated using the Nuclear Regulatory Commission's equation from Regulatory Guide 8.39 Revision 1. The results of the assays show that minimal radioactivity is present post-treatment. The results of the total effective dose equivalent estimates indicate that most cats can be released the same day of injection and that the resulting total effective dose equivalent to the cat owner is unlikely to exceed 1 mSv, suggesting that current veterinary release criteria are overly conservative.

The International Commission on Radiological Protection (ICRP) attributes the long-term retention of plutonium (Pu) in the respiratory tract partly to chemical binding, represented by the "bound fraction" within the human respiratory tract model (HRTM). Determining whether such binding occurs, and to what extent, is important for dosimetry and, consequently, for epidemiological and dose response modeling. Our analyses of data and review of literature show that the bound-fraction model fails to explain observed regional retention of Pu in the respiratory tract and contradicts many observations. To account for the observed retention of Pu in the respiratory tract of four individuals who inhaled Pu, we incorporated two mechanisms not included in current ICRP models but supported by substantial empirical evidence: (1) systemic uptake of Pu by the respiratory tract, and (2) physical encapsulation of Pu within scar tissues. Evidence of Pu in the lungs of an individual with a wound intake and in animals injected with Pu confirms and enables quantification of systemic uptake. Similarly, histological and autoradiographic observations demonstrate sequestration of Pu in fibrotic scar tissues. We therefore modified the ICRP-130 HRTM to include scar-tissue compartments, with transfer rates derived using Markov Chain Monte Carlo analyses of bioassay and post-mortem data. The model successfully described observed retention across materials ranging from soluble Pu nitrates to highly insoluble Pu oxides, predicting that scar-tissue retention accounts for 30-90% of total Pu activity in the respiratory tract, consistent with literature observations.

FLASH radiation therapy is a promising modality that delivers radiation at ultra-high dose rates, potentially minimizing normal tissue toxicity while maintaining tumor control. However, conventional dosimetry tools often fail at ultra-high dose rates, necessitating alternative solutions. Alanine dosimetry, a passive technique known for its dose-rate independence and tissue equivalence, presents a compelling option. While other studies have used alanine pellets, this study investigates the applicability of alanine powder dosimeters in FLASH radiation therapy. Thirteen dosimeters were irradiated with doses from 10 to 100 Gy using a 137 Cs source. Six samples were used to construct dose-response calibration curves, while the remaining seven were used for validation. Peak-to-peak amplitudes of the electron paramagnetic resonance signal were normalized using internal standards and sample density. Dose estimates based on density-normalized calibration were within ±4.2% of expected values, demonstrating strong linearity (R 2 > 0.99) and clinical viability. While post-processing time remains a limiting factor, this work affirms the potential of alanine powder as a reliable tool for FLASH dosimetry, especially for high-dose, dose-rate-independent measurements.

A very high dose rate of ionizing radiation (> 40 Gy s -1 , "FLASH" radiation) causes less damage to healthy cells than moderate dose rates. Following a nuclear explosion, a significant fraction of the radiation dose is delivered at this rate. Consequently, there is a potential impact on the radiation risk estimates currently in use, which are largely based on the studies of the populations of Hiroshima and Nagasaki. Based on the scientific literature covering the relevant dose range, we estimate the maximum protective effect on genetic damage is about a factor 0.6 (-40%). Using this number and the relevant dosimetry for the Life Span Study population, while excluding data doses above 4 Gy, the maximum magnitude of the effect for Hiroshima would be somewhere between 3.3% and 13.1%, depending on the dose received. These values are sensitive to the neutron relative biological effectiveness (RBE), which was assumed to be 10 in the nominal case. In Nagasaki, the magnitude varies little with the dose, between 7.3% and 9.3%, and is relatively insensitive to the neutron RBE. Nevertheless, there are some indications that a threshold for this effect around 1 Gy may be observed in biodosimetric studies of this population. Still, due to the high heterogeneity in the relevant experimental data, further research should be carried out to investigate the FLASH effect at doses relevant to epidemiology (between 0.1 to 4 Gy) instead of the higher doses used in radiotherapy, for which most research on FLASH effect is carried out.

The linear no-threshold (LNT) model was introduced into the radiological protection system by the International Commission on Radiological Protection (ICRP) in 1966. The appropriateness of this model is still hotly debated today. Based on a recently published article, we summarize recent results in radiobiology and epidemiology and discuss their impact on the use of the LNT model regarding radiological protection. The scientific results published in radiobiology and epidemiology have strengthened our scientific knowledge of cancer risks associated with low dose and/or low dose-rate radiation exposure. In radiobiology, early stages of mutational carcinogenesis are considered to play a key role in carcinogenesis, with linear responses at doses as low as 10 mGy. Today, some non-mutation mechanisms appear clearly as non-linear, but their impact on the overall carcinogenesis process remains difficult to assess. In epidemiology, excess cancer risk has been observed at dose levels of 100 mGy or less. Some findings suggest that for some cancers, non-linear dose relationships may exist, but overall, the LNT model does not seem to seriously overestimate the risks of cancer at low doses. Overall, current results in radiobiology or epidemiology do not demonstrate the existence of a dose threshold below which the risk of radiation-induced cancer would be zero. Uncertainties remain, but if such a dose threshold existed for all solid cancers, it could not be greater than a few tens of mGy. In conclusion, we consider that the recent scientific knowledge does not call into question the use of the LNT model to assess cancer risks associated with exposure to ionizing radiation for the purpose of radiological protection. Today, the use of this model seems reasonable, and no other dose-response model seems to be more appropriate or justified for radiological protection purposes.

This study focuses on recent advancements in biodosimetry using continuous wave (CW) Q-band electron paramagnetic resonance (EPR) spectroscopy and mini-biopsy samples from tooth enamel. When radiation is absorbed, the carbonate impurities in enamel (i.e., hydroxyapatite) are changed into •CO2- (carbon dioxide radical anions), which become trapped within the crystal lattice and remain stable for durations far exceeding human lifespans. This stability makes tooth enamel an ideal material for assessing radiation doses in both accident and retrospective scenarios. In contrast to traditional, more invasive CW X-band EPR (9.8 GHz) methods, the CW Q-band EPR technique allows for the non-invasive (or minimally invasive) collection of smaller enamel fragments. This enables faster, more comfortable sampling. Operating at approximately 34 GHz, CW Q-band EPR offers enhanced sensitivity and a significantly improved signal to noise ratio (S/N) compared to CW X-band EPR. This increased sensitivity is crucial for detecting lower radiation doses in smaller samples, making it particularly useful for accurately identifying high-risk individuals in radiation triage situations. For this study, mini biopsies weighing around 2 mg were extracted from teeth and analyzed at room temperature using CW Q-band EPR. Calibration curves were established using reference doses, allowing the precise calculation of doses from signal intensity. Radiation doses higher than 100 mSv were estimated with high precision and accuracy. The combination of CW Q-band EPR spectroscopy and mini-biopsy sampling of tooth enamel provides a rapid, reliable method for dose assessment in radiation triage scenarios. This advancement is essential for developing efficient biodosimetry techniques, enabling the timely identification and management of individuals exposed to ionizing radiation during radiation incidents. Additionally, this method proves invaluable for retrospective dose reconstruction in cases of chronic exposure applicable to individuals, groups, or entire populations.

Experimentally measured nuclear fragment-production cross-sections are needed for the development of cross-section models implemented in the radiation transport codes used for several endpoints, including radiation protection and health risk assessment in space. Elemental and isotopic fragment-production cross-section data have been collected from literature in a publicly available database through a combined GSI-ESA-NASA effort. The collected data for systems of interest for space exploration are discussed, and the literature gaps are indicated. The data are also compared with the nuclear fragmentation models implemented in the NASA radiation transport code HZETRN2020, namely NUCFRG3 and RAADFRG. The results show that NUCFRG3 does not take into account nuclear-structure effects, while RAADFRG does. Therefore, RAADFRG can estimate more precisely the production of certain projectile fragments, in particular helium. Nevertheless, for some systems and high energies, RAADFRG overestimates the oscillations due to odd-even effects.