Radiation epidemiology and health effects following low-level radiation exposure

Moon, Mars and Minds: Evaluating Parkinson's disease mortality among U.S. radiation workers and veterans in the million person study of low-dose effects

BACKGROUND

Radiation is one of the most important stressors related to missions in space beyond Earth's orbit. Epidemiologic studies of exposed workers have reported elevated rates of Parkinson's disease. The importance of cognitive dysfunction related to low-dose rate radiation in humans is not defined. A meta-analysis was conducted of six cohorts in the Million Person Study (MPS) of low-dose health effects to learn whether there is consistent evidence that Parkinson's disease is associated with radiation dose to brain.

MATERIALS AND METHODS

The MPS evaluates all causes of death among U.S. radiation workers and veterans, including Parkinson's disease. Systematic and consistent methods are applied to study all categories of workers including medical radiation workers, industrial radiographers, nuclear power plant workers, atomic veterans, and Manhattan Projects workers at the Los Alamos National Laboratory and at Rocky Flats. Consistent methods for all cohorts are used to estimate organ-specific doses and to obtain vital status and cause of death.

RESULTS

The meta-analysis include 6 cohorts within the MPS, consisting of 517,608 workers and 17,219,001 person-years of observation. The mean dose to brain ranged from 6.9 to 47.6 mGy and the maximum dose from 0.76 to 2.7 Gy. Five of the 6 cohorts revealed positive associations with Parkinson's disease. The overall summary estimate from the meta-analysis was statistically significant based on 1573 deaths due to Parkinson's disease. The summary excess relative risk at 100 mGy was 0.17 (95% CI: 0.05; 0.29).

CONCLUSIONS

Parkinson's disease was positively associated with radiation in the MPS cohorts indicating the need for careful evaluation as to causality in other studies, delineation of possible mechanisms, and assessing possible implications for space travel as well as radiation protection guidance for terrestrial workers.

Mortality among medical radiation workers in the United States, 1965-2016

BACKGROUND

Estimates of radiation risks following prolonged exposures at low doses and low-dose rates are uncertain. Medical radiation workers are a major component of the Million Person Study (MPS) of low-dose health effects. Annual personal dose equivalents, H_P(10), for individual workers are available to facilitate dose-response analyses for lung cancer, leukemia, ischemic heart disease (IHD) and other causes of death.

MATERIALS AND METHODS

The Landauer, Inc. dosimetry database identified 109,019 medical and associated radiation workers first monitored 1965-1994. Vital status and cause of death were determined through 2016. Mean absorbed doses to red bone marrow (RBM), lung, heart, and other organs were estimated by adjusting the recorded H_P(10) for each worker by scaling factors, accounting for exposure geometry, the energy of the incident photon radiation, sex of the worker and whether an apron was worn. There were 4 exposure scenarios: general radiology characterized by low-energy x-ray exposure with no lead apron use, interventional radiologists/cardiologists who wore aprons, nuclear medicine personnel and radiation oncologists exposed to high-energy photon radiation, and other workers. Standardized mortality ratio (SMR) analyses were performed. Cox proportional hazards models were used to estimate organ-specific radiation risks.

RESULTS

Overall, 11,433 deaths occurred (SMR 0.60; 95%CI 0.59,0.61), 126 from leukemia other than chronic lymphocytic leukemia (CLL), 850 from lung cancer, and 1654 from IHD. The mean duration of monitoring was 23.7 y. The excess relative rate (ERR) per 100 mGy was estimated as 0.10 (95% CI -0.34, 0.54) for leukemia other than CLL, 0.15 (0.02, 0.27) for lung cancer, and -0.10 (-0.27, 0.06) for IHD. The ERR for lung cancer was 0.16 (0.01, 0.32) among the 55,218 male workers and 0.09 (-0.19, 0.36) among the 53,801 female workers; a difference that was not statistically significant (p-value = 0.23).

CONCLUSIONS

Medical radiation workers were at increased risk for lung cancer that was higher among men than women, although this difference was not statistically significant. In contrast, the study of Japanese atomic bomb survivors exposed briefly to radiation in 1945 found females to be nearly 3 times the radiation risk of lung cancer compared with males on a relative scale. For medical workers, there were no statistically significant radiation associations with leukemia excluding CLL, IHD or other specific causes of death. Combining these data with other cohorts within the MPS, such as nuclear power plant workers and nuclear submariners, will enable more precise estimates of radiation risks at relatively low cumulative doses.

The satisfaction with radiology residency training in China: results of a nationwide survey

BACKGROUND

National data on the satisfaction of radiology residents enrolled in standardized residency training (SRT) are rather scarce in China. This study identified a set of potential factors concerning SRT satisfaction among radiology residents as well as the association between SRT satisfaction and post-competency and well-being.

METHODS

A total of 3666 radiology residents who were receiving SRT during 2020 in China were recruited across all 31 provinces. The cumulative odds logistic regression was used to examine the potential factors associated with SRT satisfaction as well as associations between satisfaction and well-being, burnout, professional identity and competency.

RESULTS

The prevalence of satisfaction with SRT was 68.6%. Participants who were male, worked in central China, aged more than 28 years old, had long working hours and claimed increased workload during the COVID-19 pandemic were more likely to be unsatisfied with the SRT program. Participants who were more satisfied with the radiation protection were more likely to report higher degree of SRT satisfaction (OR = 3.00, 95% CI 2.58-3.50). In addition, SRT satisfaction was positively associated with well-being, professional identity, competency and lower burnout.

CONCLUSIONS

Perceived satisfaction can be introduced into hospital management, as it may reflect the overall situation of the residents during residency training and influence radiologists' well-being, professional identification and competency. Appropriate measures should be taken to reduce the risk of radiation exposure, ensure employee safety (such as risk assessment system and paid time off), provide radiology residents with fair treatment and guarantee the time out of working for optimizing their professional ability.

Ionizing radiation, cerebrovascular disease, and consequent dementia: A review and proposed framework relevant to space radiation exposure

Space exploration requires the characterization and management or mitigation of a variety of human health risks. Exposure to space radiation is one of the main health concerns because it has the potential to increase the risk of cancer, cardiovascular disease, and both acute and late neurodegeneration. Space radiation-induced decrements to the vascular system may impact the risk for cerebrovascular disease and consequent dementia. These risks may be independent or synergistic with direct damage to central nervous system tissues. The purpose of this work is to review epidemiological and experimental data regarding the impact of low-to-moderate dose ionizing radiation on the central nervous system and the cerebrovascular system. A proposed framework outlines how space radiation-induced effects on the vasculature may increase risk for both cerebrovascular dysfunction and neural and cognitive adverse outcomes. The results of this work suggest that there are multiple processes by which ionizing radiation exposure may impact cerebrovascular function including increases in oxidative stress, neuroinflammation, endothelial cell dysfunction, arterial stiffening, atherosclerosis, and cerebral amyloid angiopathy. Cerebrovascular adverse outcomes may also promote neural and cognitive adverse outcomes. However, there are many gaps in both the human and preclinical evidence base regarding the long-term impact of ionizing radiation exposure on brain health due to heterogeneity in both exposures and outcomes. The unique composition of the space radiation environment makes the translation of the evidence base from terrestrial exposures to space exposures difficult. Additional investigation and understanding of the impact of low-to-moderate doses of ionizing radiation including high (H) atomic number (Z) and energy (E) (HZE) ions on the cerebrovascular system is needed. Furthermore, investigation of how decrements in vascular systems may contribute to development of neurodegenerative diseases in independent or synergistic pathways is important for protecting the long-term health of astronauts.

Biological and cellular responses of humans to high-level natural radiation: A clarion call for a fresh perspective on the linear no-threshold paradigm

There remains considerable uncertainty in obtaining risk estimates of adverse health outcomes of chronic low-dose radiation. In the absence of reliable direct data, extrapolation through the linear no-threshold (LNT) hypothesis forms the cardinal tenet of all risk assessments for low doses (≤ 100 mGy) and for the radiation protection principle of As Low As Reasonably Achievable (ALARA). However, as recent evidences demonstrate, LNT assumptions do not appropriately reflect the biology of the cell at the low-dose end of the dose-response curve. In this regard, human populations living in high-level natural radiation areas (HLNRA) of the world can provide valuable insights into the biological and cellular effects of chronic radiation to facilitate improved precision of the dose-response relationship at low doses. Here, data obtained over decades of epidemiological and radiobiological studies on HLNRA populations is summarized. These studies do not show any evidence of unfavourable health effects or adverse cellular effects that can be correlated with high-level natural radiation. Contrary to the assumptions of LNT, no excess cancer risks or untoward pregnancy outcomes have been found to be associated with cumulative radiation dose or in-utero exposures. Molecular biology-driven studies demonstrate that chronic low-dose activates several cellular defence mechanisms that help cells to sense, recover, survive, and adapt to radiation stress. These mechanisms include stress-response signaling, DNA repair, immune alterations and most importantly, the radiation-induced adaptive response. The HLNRA data is consistent with the new evolving paradigms of low-dose radiobiology and can help develop the theoretical framework of an alternate dose-response model. A rational integration of radiobiology with epidemiology data is imperative to reduce uncertainties in predicting the potential health risks of chronic low doses of radiation.

Occupational external exposure to ionizing radiation in research-associated activities in Iran (2015-2020)

Research is an integral part of radiological and nuclear activities; thus, workers may receive different levels of occupational exposure. In the present study, occupational external exposure of workers was studied at the largest radiological and nuclear research institute of Iran from 2015-2020. The activities included research reactors, nuclear fuel cycle, development on radiopharmaceuticals and radioisotopes, particle accelerators, plasma and fusion, and nuclear agriculture. The average doses of the monitored and exposed workers were calculated to be 0.095 and 0.575 mSv, respectively, which were around their corresponding worldwide values. Moreover, the results showed that in comparison with other research activities, the workers in research reactors, nuclear fuel cycle, and development of radiopharmaceuticals and radioisotopes may face higher occupational risks. It could be, therefore, concluded that all the radiation protection measures have been effective at achieving safe research activities in Iran.

The enduring legacy of Marie Curie: impacts of radium in 21st century radiological and medical sciences

PURPOSE

This review is focused on radium and radionuclides in its decay chain in honor of Marie Curie, who discovered this element.

MATERIALS AND METHODS

We conglomerated current knowledge regarding radium and its history predating our present understanding of this radionuclide.

RESULTS

An overview of the properties of radium and its dose assessment is shown followed by discussions about both the negative detrimental and positive therapeutic applications of radium with this history and its evolution reflecting current innovations in medical science.

CONCLUSIONS

We hope to remind all those who are interested in the progress of science about the vagaries of the process of scientific discovery. In addition, we raise the interesting question of whether Marie Curie's initial success was in part possible due to her tight alignment with her husband Pierre Curie who pushed the work along.

Effects of low dose ionizing radiation on the brain- a functional, cellular, and molecular perspective

Over the years, the advancement of radio diagnostic imaging tools and techniques has radically improved the diagnosis of different pathophysiological conditions, accompanied by increased exposure to low-dose ionizing radiation. Though the consequences of high dose radiation exposure on humans are very well comprehended, the more publicly relevant effects of low dose radiation (LDR) (≤100 mGy) exposure on the biological system remain ambiguous. The central nervous system, predominantly the developing brain with more neuronal precursor cells, is exceptionally radiosensitive and thus more liable to neurological insult even at low doses, as shown through several rodent studies. Further molecular studies have unraveled the various inflammatory and signaling mechanisms involved in cellular damage and repair that drive these physiological alterations that lead to functional alterations. Interestingly, few studies also claim that LDR exerts therapeutic effects on the brain by initiating an adaptive response. The present review summarizes the current understanding of the effects of low dose radiation at functional, cellular, and molecular levels and the various risks and benefits associated with it based on the evidence available from in vitro, in vivo, and clinical studies. Although the consensus indicates minimum consequences, the overall evidence suggests that LDR can bring about considerable neurological effects in the exposed individual, and hence a re-evaluation of the LDR usage levels and frequency of exposure is required.

Overview of epidemiological studies of nuclear workers: opportunities, expectations, and limitations. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2021;41:1075-1092. [PMID: 34161930 DOI: 10.1088/1361-6498/ac0df4]

Epidemiological studies of those exposed occupationally to ionising radiation offer an important opportunity to directly check the assumptions underlying the international system of radiological protection against low-level radiation exposures. Recent nuclear worker studies, notably the International Nuclear Workers Study (INWORKS) and studies of the Mayak workforce in Russia, provide powerful investigations of a wide range of cumulative photon doses received at a low dose-rate over protracted periods, and broadly confirm radiation-related excess risks of leukaemia and solid cancers at around the levels predicted by standard risk models derived mainly from the experience of the Japanese atomic-bomb survivors acutely exposed principally to gamma radiation. However, the slope of the dose-response for solid cancers expressed in terms of the excess relative risk per unit dose, ERR/Gy, differs between INWORKS and Mayak, such that when compared with the slope derived from the atomic-bomb survivors, INWORKS does not provide obvious support for the use in radiological protection of a dose and dose-rate effectiveness factor greater than one whereas the Mayak workforce apparently does. This difference could be a chance effect, but it could also point to potential problems with these worker studies. Of particular concern is the adequacy of recorded doses received in the early years of operations at older nuclear installations, such as the potential for 'missed' photon doses. A further issue is how baseline cancer rates may influence radiation-related excess risks. There is scope for a considerable increase in the statistical power of worker studies, with longer follow-up capturing more deaths and incident cases of cancer, and further workforces being included in collaborative studies, but the difficulties posed by dosimetry questions should not be ignored and need to be the subject of detailed scrutiny.

A million persons, a million dreams: a vision for a national center of radiation epidemiology and biology

BACKGROUND

Epidemiologic studies of radiation-exposed populations form the basis for human safety standards. They also help shape public health policy and evidence-based health practices by identifying and quantifying health risks of exposure in defined populations. For more than a century, epidemiologists have studied the consequences of radiation exposures, yet the health effects of low levels delivered at a low-dose rate remain equivocal.

MATERIALS AND METHODS

The Million Person Study (MPS) of U.S. Radiation Workers and Veterans was designed to examine health effects following chronic exposures in contrast with brief exposures as experienced by the Japanese atomic bomb survivors. Radiation associations for rare cancers, intakes of radionuclides, and differences between men and women are being evaluated, as well as noncancers such as cardiovascular disease and conditions such as dementia and cognitive function. The first international symposium, held November 6, 2020, provided a broad overview of the MPS. Representatives from four U.S. government agencies addressed the importance of this research for their respective missions: U.S. Department of Energy (DOE), the Centers for Disease Control and Prevention (CDC), the U.S. Department of Defense (DOD), and the National Aeronautics and Space Administration (NASA). The major components of the MPS were discussed and recent findings summarized. The importance of radiation dosimetry, an essential feature of each MPS investigation, was emphasized.

RESULTS

The seven components of the MPS are DOE workers, nuclear weapons test participants, nuclear power plant workers, industrial radiographers, medical radiation workers, nuclear submariners, other U.S. Navy personnel, and radium dial painters. The MPS cohorts include tens of thousands of workers with elevated intakes of alpha particle emitters for which organ-specific doses are determined. Findings to date for chronic radiation exposure suggest that leukemia risk is lower than after acute exposure; lung cancer risk is much lower and there is little difference in risks between men and women; an increase in ischemic heart disease is yet to be seen; esophageal cancer is frequently elevated but not myelodysplastic syndrome; and Parkinson's disease may be associated with radiation exposure.

CONCLUSIONS

The MPS has provided provocative insights into the possible range of health effects following low-level chronic radiation exposure. When the 34 MPS cohorts are completed and combined, a powerful evaluation of radiation-effects will be possible. This final article in the MPS special issue summarizes the findings to date and the possibilities for the future. A National Center for Radiation Epidemiology and Biology is envisioned.

Mortality from Leukemia, Cancer and Heart Disease among U.S. Nuclear Power Plant Workers, 1957-2011

BACKGROUND

The aim of the Million Person Study (MPS) of Low Dose Health Effects is to examine the level of radiation risk for chronic exposures received gradually over time and not acutely as was the case for the Japanese atomic bomb survivors. Nuclear power plant (NPP) workers comprise nearly 15 percent of the MPS. Leukemia, selected cancers, Parkinson's disease, ischemic heart disease (IHD) and other causes of death are evaluated.

METHODS AND MATERIAL

The U.S. Nuclear Regulatory Commission's Radiation Exposure Information and Reporting System (REIRS) and the Landauer, Inc. dosimetry databases identified 135,193 NPP workers first monitored 1957-1984. Annual personal dose equivalents [Hp(10)] were available for each worker. Radiation records from all places of employment were sought. Vital status was determined through 2011. Mean absorbed doses to red bone marrow (RBM), esophagus, lung, colon, brain and heart were estimated by adjusting the recorded Hp(10) for each worker by scaling factors, accounting for exposure geometry and energy of the incident gamma radiation. Standardized mortality ratios (SMR) were calculated. Radiation risks were estimated using Cox proportional hazards models.

RESULTS

Nearly 50% of workers were employed for more than 20 years. The mean duration of follow-up was 30.2 y. Overall, 29,076 total deaths occurred, 296 from leukemia other than chronic lymphocytic leukemia (CLL), 3,382 from lung cancer, 140 from Parkinson's disease and 5,410 from IHD. The mean dose to RBM was 37.9 mGy (maximum 1.0 Gy; percent >100 mGy was 9.2%), 43.2 mGy to lung, 43.7 mGy to colon, 33.2 mGy to brain, and 43.9 mGy to heart. The SMRs (95% CI) were 1.06 (0.94;1.19) for leukemia other than CLL, 1.10 (1.07;1.14) for lung cancer, 0.90 (0.76;1.06) for Parkinson's disease, and 0.80 (0.78; 0.82) for IHD. The excess relative risk (ERR) per 100 mGy for leukemia other than CLL was 0.15 (90% CI 0.001; 0.31). For all solid cancers the ERR per 100 mGy (95% CI) was 0.01 (-0.03; 0.05), for lung cancer -0.04 (-0.11; 0.02), for Parkinson's disease 0.24 (-0.02; 0.50), and for IHD -0.01 (-0.06; 0.04).

CONCLUSION

Prolonged exposure to radiation increased the risk of leukemia other than CLL among NPP workers. There was little evidence for a radiation-association for all solid cancers, lung cancer or ischemic heart disease. Increased precision will be forthcoming as the different cohorts within the MPS are combined, such as industrial radiographers and medical radiation workers who were assembled and evaluated in like manner.

Control of Neuroinflammation through Radiation-Induced Microglial Changes

Microglia, the innate immune cells of the central nervous system, play a pivotal role in the modulation of neuroinflammation. Neuroinflammation has been implicated in many diseases of the CNS, including Alzheimer's disease and Parkinson's disease. It is well documented that microglial activation, initiated by a variety of stressors, can trigger a potentially destructive neuroinflammatory response via the release of pro-inflammatory molecules, and reactive oxygen and nitrogen species. However, the potential anti-inflammatory and neuroprotective effects that microglia are also thought to exhibit have been under-investigated. The application of ionising radiation at different doses and dose schedules may reveal novel methods for the control of microglial response to stressors, potentially highlighting avenues for treatment of neuroinflammation associated CNS disorders, such as Alzheimer's disease and Parkinson's disease. There remains a need to characterise the response of microglia to radiation, particularly low dose ionising radiation.

Occupational and Patient Radiation Dose and Quality Implications of Femoral Access Imaging During Coronary Angiography

Purpose

Cardiologists often perform angiography of the common femoral artery (CFA) access site to evaluate whether the anatomy is suitable for deployment of a vascular closure device or to assess whether iatrogenic vessel damage has occurred. The choice of acquisition mode has radiation dose implications. The objective of this study was to investigate the influence of the selected type of CFA x-ray imaging mode (fluoro save, cine acquisition and digital subtraction angiography (DSA)) and tube angle on patient and staff dose during coronary angiography.

Materials and Methods

Assessment of image quality for the different modes was performed to determine whether lower dose modes provide images of sufficient clinical quality to be routinely employed. Radiation dose levels for the patients (n=782), cardiologists (n=17), scrub nurses (n=27) and scout nurses (n=32) were measured in a prospective single-centre study between February 2017 and August 2019. Three Philips angiographic units and DoseAware dose monitoring systems were used.

Results

Among the acquisition modes, fluoro save provided acceptable diagnostic quality for visualizing femoral access points and diagnosing pathology in 99% of cases. Average patient dose area product (DAP) was 83.95, 742.50, and 3363.41mGy² and average patient air kerma (AK) was 0.87, 8.44, and 18.61mGy for fluoro save, cine, and DSA acquisitions, respectively. The use of higher dose imaging modes, imaging in the contralateral view and utilizing steeper TA was associated with a higher patient dose. Due to staff dose being highly correlated with DAP and AK, it was difficult to observe any association between staff dose and CFA imaging mode. However, this does not discount a potential increase in occupational dose due to the use of cine angiography or digital subtraction angiography during CFA imaging.

Conclusion

DSA of the CFA should be avoided during transfemoral coronary angiography unless critical to diagnostic analysis. It is recommended that fluoroscopic operators consider utilizing lower dose modes in the ipsilateral orientation ≤32° TA to reduce the risk of patient and staff radiation exposure.

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Mortality among workers at the Los Alamos National Laboratory, 1943-2017

BACKGROUND

During World War II (WWII), the Manhattan Engineering District established a secret laboratory in the mountains of northern New Mexico. The mission was to design, construct and test the first atomic weapon, nicknamed 'The Gadget' that was detonated at the TRINITY site in Alamogordo, NM. After WWII, nuclear weapons research continued, and the laboratory became the Los Alamos National Laboratory (LANL).

MATERIALS AND METHODS

The mortality experience of 26,328 workers first employed between 1943 and 1980 at LANL was determined through 2017. Included were 6157 contract workers employed by the ZIA Company. Organ dose estimates for each worker considered all sources of exposure, notably photons, neutrons, tritium, ²³⁸Pu and ²³⁹Pu. Vital status determination included searches within the National Death Index, Social Security Administration and New Mexico State Mortality Files. Standardized Mortality Ratios (SMR) and Cox regression models were used in the analyses.

RESULTS

Most workers (55%) were hired before 1960, 38% had a college degree, 25% were female, 81% white, 13% Hispanic and 60% had died. Vital status was complete, with only 0.1% lost to follow-up. The mean dose to the lung for the 17,053 workers monitored for radiation was 28.6 weighted-mGy (maximum 16.8 weighted-Gy) assuming a Dose Weighting Factor of 20 for alpha particle dose to lung. The Excess Relative Risk (ERR) at 100 weighted-mGy was 0.01 (95%CI -0.02, 0.03; n = 839) for lung cancer. The ERR at 100 mGy was -0.43 (95%CI -1.11, 0.24; n = 160) for leukemia other than chronic lymphocytic leukemia (CLL), -0.06 (95%CI -0.16, 0.04; n = 3043) for ischemic heart disease (IHD), and 0.29 (95%CI 0.02, 0.55; n = 106) for esophageal cancer. Among the 6499 workers with measurable intakes of plutonium, an increase in bone cancer (SMR 2.44; 95%CI 0.98, 5.03; n = 7) was related to dose. The SMR for berylliosis was significantly high, based on 4 deaths. SMRs for Hispanic workers were significantly high for cancers of the stomach and liver, cirrhosis of the liver, nonmalignant kidney disease and diabetes, but the excesses were not related to radiation dose.

CONCLUSIONS

There was little evidence that radiation increased the risk of lung cancer or leukemia. Esophageal cancer was associated with radiation, and plutonium intakes were linked to an increase of bone cancer. IHD was not associated with radiation dose. More precise evaluations will await the pooled analysis of workers with similar exposures such as at Rocky Flats, Savannah River and Hanford.

Organ-Specific Effects of Low Dose Radiation Exposure: A Comprehensive Review

Ionizing radiation (IR) is a high-energy radiation whose biological effects depend on the irradiation doses. Low-dose radiation (LDR) is delivered during medical diagnoses or by an exposure to radioactive elements and has been linked to the occurrence of chronic diseases, such as leukemia and cardiovascular diseases. Though epidemiological research is indispensable for predicting and dealing with LDR-induced abnormalities in individuals exposed to LDR, little is known about epidemiological markers of LDR exposure. Moreover, difference in the LDR-induced molecular events in each organ has been an obstacle to a thorough investigation of the LDR effects and a validation of the experimental results in in vivo models. In this review, we summarized the recent reports on LDR-induced risk of organ-specifically arranged the alterations for a comprehensive understanding of the biological effects of LDR. We suggested that LDR basically caused the accumulation of DNA damages, controlled systemic immune systems, induced oxidative damages on peripheral organs, and even benefited the viability in some organs. Furthermore, we concluded that understanding of organ-specific responses and the biological markers involved in the responses is needed to investigate the precise biological effects of LDR.