Traditionally, the dicentric chromosome assay is performed on large vessels with lymphocyte cultures of 3-5 mL. Our aim was to enhance usability in different settings, focusing on irradiating a thin cell layer to target cells with low-penetration radiation and to handle large-scale triage situations. To achieve this, protocols for irradiation, culture, and metaphase fixation using a MIDI format in 48-well plates were developed. Using 100 μL of isolated lymphocytes in these plates, we systematically optimized cell density, mitogenic stimulation, cell cycle arrest, and metaphase fixation. The semi-automated dicentric scoring with DCSore exhibited a linear-quadratic dose-response relationship up to 8 Gy. This dose-response curve was validated with irradiated and blinded blood samples. The MIDI format provides a reproducible, scaled-down alternative to the classic DCA protocol, enabling exposure of cells to low-penetration radiation and being suitable for both emergency triage and routine biodosimetry.

After a large-scale radiation incident such as the detonation of an improvised nuclear device, an unplanned release of radiation from a nuclear power plant, or the deployment of a radiation dispersal device, many people who were near the incident will seek medical reassurance, despite the low likelihood of experiencing clinically significant radiation exposure. This group, often called the "worried well," if not addressed separately, could overwhelm facilities and services designed to triage individuals who received high doses of radiation. Therefore, it is crucial to address this group's needs directly and estimate their numbers. Current biodosimetry methods are tailored for triage and dose estimation in individuals with significant exposures. Since first responders and healthcare workers will likely focus on high-dose cases, new methods are needed to serve the worried well. These could involve individuals collecting samples themselves and either reading them at home or transporting them to centers for analysis. Such methods must be able to use parameters valid for periods longer than two weeks. For example, one promising approach is electron paramagnetic resonance (EPR) analysis of radiation-induced free radicals in nail clippings. Developing this or other techniques capable of managing the large numbers of worried well, likely to be individuals with insignificant radiation exposure, will require sustained dedicated effort.

Proton therapy (PT) and carbon-ion therapy (CIT) differ not only in their physical dose characteristics but also in their biological effects, attributable to variations in fractionation protocols and linear energy transfer (LET). These differences make direct comparisons challenging. This study aims to comprehensively compare the treatment planning of protons and carbon ions for head and neck cancer by incorporating LET-dependent variable α/β ratios into the calculations of equivalent dose in 2 Gy fractions (EQD2) and normal tissue complication probability (NTCP). We retrospectively created treatment plans for nine head and neck cancer patients using proton therapy and carbon-ion therapy. Variable α/β ratios, calculated via the microdosimetric kinetic model, were integrated into EQD2 calculations. NTCP assessments for both late and acute toxicities utilized the Lyman-Kutcher-Burman model. In addition to comparing EQD2 and NTCP outcomes between protons and carbon ions, we conducted robustness evaluations that considered a 2 mm positioning error and a 3.5% range uncertainty. The α/β ratio for protons remained consistent at approximately 3 Gy across all tissues. In contrast, the α/β ratio for carbon ions varied significantly, reaching up to 20 Gy along the beam path. This variability in α/β ratios showed that carbon ions achieved lower EQD2 values for organs at risk (OARs) such as the brain, skin, and oral mucosa compared to protons. Furthermore, NTCP analysis revealed a significant reduction in acute toxicities, particularly dermatitis, with carbon-ion therapy. Both treatment modalities effectively minimized the probability of late toxicities. No significant differences in robustness were observed between proton therapy and carbon-ion therapy. EQD2 calculations incorporating variable α/β ratios revealed that carbon ions offer a dosimetric advantage over protons for certain OARs. However, this difference was relatively minor and did not suggest a clinically significant impact beyond acute toxicities.

In the event of a criticality accident, there is a risk of high-dose exposure for affected individuals from a mixed gamma-neutron radiation field. Dosimetry in such cases is complex and requires multiple approaches. Biodosimetry methods, especially the dicentric chromosome assay (DCA), the most established method, can significantly support triage and medical care decisions after a criticality incident. However, large-scale events need collaboration between laboratories to enable timely dose assessments using DCA. We conducted a comparison among three biodosimetry laboratories, focusing on DCA-based estimates of the total dose, including the specific gamma-ray dose and neutron-heavy-particle dose for blood samples irradiated in a mixed gamma-neutron field. Although each laboratory used dose-effect curves derived from different radiation spectra and irradiation facilities, the dose estimates were acceptable, with relative deviations no greater than 21%. Overall, the study showed that collaborating between labs is feasible for individual dose estimation after a criticality accident.

A cohort mortality study was conducted of 123,401 industrial radiographers in the United States to estimate risks following protracted radiation exposures. The cohort was constructed from the Nuclear Regulatory Commission Radiation Exposure Information Reporting System and the Landauer, Inc. dosimetry databases. Workers were monitored between 1939 and 2011 and were exposed mainly to external gamma radiation from 192Ir and 60Co. Causes of death were obtained from the National Death Index and state mortality files with follow-up through 2019. The mean duration of follow-up was 27.7 years. Nearly 19% of workers were monitored for more than 10 years. There were 30,617 (24.8%) who worked at shipyards and 5,071 (4.1%) at nuclear power plants with the potential for asbestos exposure. The mean radiation dose to the red bone marrow (RBM) was 15.2 mGy (maximum 1.24 Gy; percent >100 mGy was 3.6%), 17.2 mGy to lung, 18.1 mGy to colon, 11.9 mGy to brain, and 18.1 mGy to heart. Overall, 30,560 deaths occurred; the Standardized Mortality Ratio and 95% confidence interval for all-cause mortality was 0.92 95% CI (0.91, 0.93); for all solid cancers 1.01 (0.99, 1.03; n = 7,734); for ischemic heart disease (IHD) 0.83 (0.81, 0.85; n = 5,820); for cerebrovascular disease (CeVD) 0.88 (0.83, 0.93; n = 1,257); for mesothelioma 6.08 (5.35, 6.89; n = 248); and for asbestosis 13.4 (11.2, 15.9; n = 134). The Cox linear excess relative risk (ERR) per 100 mGy (95% CI) for leukemia (excluding CLL) was 0.45 (0.05, 0.85) and for non-Hodgkin lymphoma (NHL) was 0.33 (0.04, 0.62). For all solid cancers it was 0.06 (0.02, 0.10); lung cancer 0.11 (0.04, 0.19); all solid cancers excluding lung cancer and mesothelioma 0.02 (-0.03, 0.07); Parkinson's disease 0.24 (-0.13, 0.61); IHD -0.03 (-0.06, 0.01); and CeVD 0.05 (-0.08, 0.17). The ERR per 100 mGy for chronic obstructive pulmonary disease (COPD) was 0.19 (0.08, 0.30) and was similar in magnitude to that for lung cancer. This finding suggests that residual confounding by smoking may have influenced the results, warranting cautious interpretations. No significant association was found between cumulative radiation exposure and all solid cancers after excluding lung cancer and mesothelioma, nor for IHD or CeVD. The marginally non-significant increased risk of Parkinson's disease, also seen in other Million Person Study cohorts, requires further investigation. Early workers monitored entirely before 1979 had the same linear ERR per 100 mGy for solid cancers [0.06 (0.00, 0.12) n = 3,587] as for all other more contemporary workers monitored after 1978 [0.07 (0.01,0.13) n = 4,150]. This report provides convincing evidence that low-dose and low-dose-rate exposures over time significantly increases the risk of leukemia (excluding CLL) following cumulative doses up to 200 mGy while also providing information on early versus contemporary workers.

Radiation-induced senescence (RIS) is thought to be one mechanism by which tumor cells can survive radiation-induced cell death. Accumulating evidence suggests that therapy-induced senescence (TIS) (triggered by both chemotherapy and/or irradiation) also facilitates tumor cell recovery, thereby contributing to disease recurrence. Furthermore, the factors secreted by senescent tumor cells (the senescence-associated secretory phenotype (SASP)) have, in some cases, been reported to be tumor-promoting, immunosuppressive, and potentially responsible for some of the adverse effects of radiation. Given these largely undesirable attributes of RIS in tumor cells, the use of senolytic agents to eliminate senescent tumor cells has been investigated in preclinical studies. An analysis of the available literature on RIS in cell culture models tends to support the utility of the Bcl-xL/Bcl-2/Bcl-w-targeting agent ABT-263 (navitoclax), in combination with a single high-dose of radiation and, in some cases, with fractionated irradiation. However, because drug action has also been reported when administered prior to irradiation, prior tumor cell entry into senescence may not be obligatory for enhancement of radiation sensitivity by ABT-263. This conclusion is also consistent with drug action against tumor cells with low RIS levels, such as those induced by fractionated irradiation. While a relatively small number of studies in tumor-bearing animals demonstrate the effectiveness of ABT-263 in combination with radiation invivo, once the drug pressure has been relaxed, the tumor cells likely still retain the capacity to recover proliferative capacity. Since ABT-263 is unlikely to be approved for the clinical treatment of solid tumors due to both on-target (thrombocytopenia) and off-target (neutropenia) toxicities, the few studies indicating improved radiosensitivity with ABT-199 (venetoclax) are intriguing, suggesting that targeting of Bcl-xL may not be a strict requirement for the combination strategy. Finally, it is worth noting that senolytic agents have the potential to protect normal tissue from radiation-induced damage, which may prove to be the most clinically relevant observation for this class of drugs.

Leukemia stem cells (LSCs) are a key factor leading to the recurrence and drug resistance in acute myeloid leukemia (AML). Notably, the persistence of radiotherapy-resistant LSCs has been identified as a critical determinant of post-hematopoietic stem cell transplantation (HSCT) relapse. Herein, we report glutathione peroxidase 1 (GPX1) as a promising target for eliminating LSCs after exposure to ionizing radiation. Silencing GPX1 in LSCs robustly triggers cell death and cell cycle arrest, thereby enhancing the radiosensitivity of LSCs. Specifically, GPX1 maintains the survival and proliferation of LSCs by regulating redox homeostasis. Upon GPX1 knockdown, intracellular reactive oxygen species (ROS) accumulate, which in turn impairs the function of BCL2 and ultimately triggers LSC apoptosis. After radiation exposure, ROS scavengers can effectively rescue GPX1 knockdown-induced LSC apoptosis and restore their impaired proliferative capacity. Accordingly, our study reveals GPX1 function in LSC maintenance and radiation tolerance, providing a therapeutic opportunity for ablating LSCs and for AML targeted therapy.

Increased leukemia incidence or mortality is a well-known effect of acute radiation exposure. Less is known about the risks associated with protracted exposure, such as those arising in occupational exposure settings. We used excess relative risk models to investigate the strength of evidence for and the shape of the dose response for mortality from leukemia (excluding chronic lymphocytic leukemia, CLL) in the Russian Mayak Worker Cohort. The cohort includes 25,757 workers followed for cancer mortality from 1948 to 2015 who were subject to both external low-dose-rate gamma ray and internal exposures (from alpha particles emitted by inhaled plutonium). The red bone marrow external dose estimates were based on individual readings from film badges or TLD dosimeters. The mean external marrow dose was 584 mGy for workers hired before 1959 and 105 mGy for those hired between 1959 and 1982. Internal exposures were described using red bone marrow alpha-particle dose for workers who were subject to plutonium monitoring and potential plutonium exposure categories for unmonitored workers. The mean marrow dose from internal exposure for monitored workers was 2.1 mGy for those hired before 1959 and 0.16 mGy for those hired between 1959 and 1982. Radiation effects were described using both excess relative rate (ERR) and excess absolute rate (EAR) models. The excess relative rates for the 96 deaths from non-CLL leukemia were described using a time-since-exposure-dependent quadratic response in cumulative external low LET dose with effect modification by attained age. While the largest ERRs [2.45 at 1 Gy, 95% confidence interval (CI) 0.33 to 11.9] were associated with external doses received between 2 and 5 years before death, there was also a significant increase in rates for doses received 5 or more years before death (ERR 0.28 at 1 Gy, 95% CI 0.06 to 0.72) and an indication of increased rates associated with doses within two years of death (ERR 1.47 at 1 Gy, 95% CI 0.06 to 10.6). Uncertainties in these excess relative rate estimates from the primary models were adjusted for dose uncertainty. Excess absolute rate (EAR) models were also used to describe the leukemia death rates. The pattern of the EAR variation with time-since-exposure was like that for the ERR Doses received 2 to 4 years before death had the largest EAR (ERR 4.78 per 10,000 person years per Gy2, 94% CI 1.75 to 10.7) with increased rates for doses received within two years of death (3.66, 95% CI 9.26 to 11.2), and for doses received 5 or more years before death (0.34, 95% CI 0.11 to 0.7). However, while the ERR decreased with increasing attained age, there was no indication of an attained age dependence in the EAR. The external-exposure radiation-associated leukemia risk appeared to be largely from acute myeloid leukemia. There was no evidence of external exposure effects on the risks of death from chronic lymphocytic leukemia, lymphoma, or multiple myeloma. There was no evidence of internal exposure effects on the rates of leukemia or other lymphohematopoietic malignancies. These analyses extend earlier studies of leukemia mortality in the Mayak worker cohort, with additional years of follow-up, utilize the latest bone marrow dose estimates, and include an assessment of the effect of shared dose uncertainty on risk uncertainty. Our results show significant excess risk for non-CLL leukemia mortality with a complex interaction between attained age, time since exposure, and age at exposure. The highest risk per unit dose was associated with exposures received 2-5 years before the time at risk. In addition, for a given total cumulative dose, the risk decreases rapidly with increasing attained age. We discuss the differences between the patterns of risk related to acute exposures in the Life Span Study of survivors of the atomic bombings in Hiroshima and Nagasaki, and chronic exposure in the Mayak Worker Cohort as well as differences between risk estimates in our study and others involving prolonged low-dose external gamma ray exposure.

Head and neck squamous cell carcinoma (HNSCC) resistance to radiotherapy has prompted a need to develop adaptive radiation therapy protocols to improve patient outcomes. This study investigates the hypothesis that lipid metabolism regulates cell cycle phase-specific radiation sensitivity of HNSCC cells. Previous studies have shown that HNSCC tumors with a higher proportion of G0/G1 phase cells (low proliferative index, LPI) are more resistant to radiation compared to HNSCC tumors with a higher proportion of S/G2 phase cells (high proliferative index, HPI). RNA-seq and bioinformatics identified lipid metabolism as the major intrinsic pathway that differs between HPI and LPI HNSCC cultures. mRNA and protein levels of G0/G1 Switch 2 gene (G0S2), regulator of quiescence and lipid metabolism, were upregulated in LPI compared to HPI HNSCC cultures. G0S2 negatively regulates adipose triglyceride lipase (ATGL), resulting in less lipolytic activity. siG0S2 treatment of LPI cultures recruited cells into the proliferative cycle and exacerbated radiation sensitivity. To override G0S2 action, we incubated LPI cultures with the fatty acid palmitate and examined cellular metabolic stress markers. Compared to controls, LPI cultures treated with palmitate showed increased reactive oxygen species levels, lipid peroxidation and oxygen consumption rate coupled with increased mitochondrial fission. Furthermore, using the fluorescent based cell cycle real-time imaging system, we showed that palmitate treatment sustained cell proliferation (higher S/G2) compared to controls (higher G1). Palmitate treatment resulted in significant sensitization to radiation treatment and enhanced the efficacy of poly (ADP-ribose) polymerase (PARP) inhibitors. In summary, we demonstrate that G0S2-dependent lipid metabolism regulates cell cycle phase-specific radiation sensitivity of HNSCC cells and identify G0S2 and free fatty acids as novel targets for radiation therapy.

DNA double-strand breaks (DSBs) are the most severe type of DNA damage in living organisms and are primarily repaired by two pathways: non-homologous end joining (NHEJ) and homologous recombination (HR). DNA ligase IV (LIG4) is essential for the final step of NHEJ, where it facilitates the rejoining of DSBs. Loss-of-function mutations in the LIG4 gene result in LIG4 syndrome, a condition characterized by combined immunodeficiency, developmental delay, microcephaly and radiosensitivity. In this study, we investigated cellular senescence, radiosensitivity, and X-ray radiation-induced chromosome aberrations induced in newly developed Lig4 mutant (Lig4W447C/W447C) mouse cells. The results showed that Lig4W447C/W447C cells exhibited accelerated cellular senescence, possibly due to increased accumulation of spontaneous DSBs. Radiosensitivity assays revealed that Lig4W447C/W447C cells were four times more radiosensitive than wild-type cells. Moreover, analysis of both X-ray radiation-induced chromatid-type and chromosome-type aberrations revealed that both break-type aberrations (e.g., fragments) and exchange-type aberrations (e.g., dicentrics) were increased in Lig4W447C/W447C cells compared to wild-type cells. These results suggest that in addition to causing inefficient DNA break, end-joining, the novel mutation in Lig4 may promote misrejoining of X-ray radiation-induced DSBs.