A simulation approach to predict the calibration curve of low LET radiations for biological dosimetry using the Geant4-DNA toolkit

Ionizing radiation is extensively utilized in various applications; however, it can lead to significant harm to living systems. In this regard, the radiation absorbed dose is usually evaluated by performing biological dosimetry and physical reconstruction of exposure scenarios. But, this is costly, time-consuming, and maybe impractical for a biodosimetry lab to perform biological dosimetry. This study aimed to assess the applicability and reliability of the Geant4-DNA toolkit as a simulation approach to construct a reliable dose-response curve for biodosimetry purposes as an appropriate substitution for experimental measurements. In this matter, the total number of double-strand breaks (DSBs), due to different doses of low LET radiation qualities on DNA molecules, was calculated and converted to the values of dicentric chromosomes using a mechanistic model of cellular response. Then, the number of dicentric chromosomes induced by 200 kVp X-rays were modified by using a semi-empirical scaling factor for compensating the restriction of simulation code to consider what can happen in a real cell. Next, the trend of dicentrics for 137Cs and 60Co were calculated and modified by the above scaling factor. Finally, the dose-response curves for these gamma sources compared to several published experiments. The suggested calibration curves for 137Cs and 60Co followed a linear quadratic equation: Ydic = 0.0054 (± 0.0133) - 0.0089 (± 0.0212) × D + 0.0568 (± 0.0051) × D2 and Ydic = 0.0052 (± 0.0128) - 0.00568 (± 0.0203) × D + 0.0525 (± 0.0049) × D2 respectively. They revealed a satisfactory agreement with the experimental data reported by others. The Geant4 program developed in this work could provide an appropriate tool for predicting the dose-response (calibration) curve for biodosimetry purposes.

Contribution of Biological and EPR Dosimetry to the Medical Management Support of Acute Radiation Health Effects

In this review, we discuss the value of biological dosimetry and electron paramagnetic resonance (EPR) spectroscopy in the medical management support of acute radiation syndrome (ARS). Medical management of an ionizing radiation scenario requires significant information. For optimal medical aid, this information has to be rapidly (< 3 days) delivered to the health-care provider. Clinical symptoms may initially enable physicians to predict ARS and initiate respective medical treatment. However, in most cases at least further verification through knowledge on radiation exposure details is necessary. This can be assessed by retrospective dosimetry techniques, if it is not directly registered by personal dosimeters. The characteristics and potential of biological dosimetry and electron paramagnetic resonance (EPR) dosimetry using human-derived specimen are presented here. Both methods are discussed in a clinical perspective regarding ARS diagnostics. The presented techniques can be used in parallel to increase screening capacity in the case of mass casualties, as both can detect the critical dose of 2 Gy (whole body single dose), where hospitalization will be considered. Hereby, biological dosimetry based on the analysis of molecular biomarkers, especially gene expression analysis, but also in vivo EPR represent very promising screening tools for rapid triage dosimetry in early-phase diagnostics. Both methods enable high sample throughput and potential for point-of-care diagnosis. In cases of higher exposure or in small-scale radiological incidents, the techniques can be used complementarily to understand important details of the exposure. Hereby, biological dosimetry can be employed to estimate the whole body dose, while EPR dosimetry on nails, bone or teeth can be used to determine partial body doses. A comprehensive assessment will support optimization of further medical treatment. Ultimately, multipath approaches are always recommended. By tapping the full potential of all diagnostic and dosimetric methods, effective treatment of patients can be supported upon exposure to radiation.

Use of Biological Dosimetry for Monitoring Medical Workers Occupationally Exposed to Ionizing Radiation

Medical workers are the largest group exposed to man-made sources of ionizing radiation. The annual doses received by medical workers have decreased over the last several decades, however for some applications, like fluoroscopically guided procedures, the occupational doses still remain relatively high. Studies show that for some procedures the operator and staff still use insufficient protective and dosimetric equipment, which might cause an underestimation of medical exposures. Physical dosimetry methods are a staple for estimating occupational exposures, although due to the inconsistent use of protection measures, an alternative method such as biological dosimetry might complement the physical methods to achieve a more complete picture. Such methods were used to detect exposures to doses as low as 0.1 mSv/year, and could be useful for a more accurate assessment of genotoxic effects of ionizing radiation in medical workers. Biological dosimetry is usually based on the measurement of the effects present in peripheral blood lymphocytes. Although some methods, such as chromosome aberration scoring or micronucleus assay, show promising results, currently there is no one method recognized as most suitable for dosimetric application in the case of chronic, low-dose exposures. In this review we decided to evaluate different methods used for biological dosimetry in assessment of occupational exposures of medical workers.