In situ determination of 137Cs inventory in soil using a field-portable scintillation gamma spectrometer-dosimeter.

A new empirical method for in situ determination of the inventory of 137Cs in soil (ACs, kBq m-2) at grasslands and forests using a field-portable NaI(Tl) scintillation spectrometer-dosimeter was developed. The method is based on evaluation of the ambient dose equivalent build-up factor. The practical implementation of the new method with the spectrometer-dosimeter does not require a priori knowledge of the vertical distribution of 137Cs in soil. Moreover, the method allows assessing a value of the mean migration depth of 137Cs in soil (Z) in terms of g cm-2. The 95% confidence interval for the mean value of the conversion coefficients from the ambient dose equivalent build-up factor to ACs and to Z is less than 10%. The new method has been developed and verified using published data that where obtained at territories in Russia and Belarus heavily contaminated with 137Cs (ACs > 37 kBq m-2) due to the Chernobyl accident. Therefore, the survey of less contaminated areas requires additional validation of this method.

Calculation of the effective external dose rate to a person staying in the resettlement zone of the Vetka district of the Gomel region of Belarus based on in situ and ex situ assessments in 2016-2018.

The aim of this study was to perform a preliminary assessment of the expected effective dose rate from external exposure to an adult individual staying at that part of the radioactively contaminated territory of the Vetka district of the Gomel region of the Republic of Belarus, from where residents had been resettled after the Chernobyl accident. For this assessment, in summer 2016 and 2018 soil samples were taken from 19 sites located in forests (7 plots), virgin meadows (4 plots), cultivated meadows (6 plots) and vegetable gardens (2 plots), with the subsequent estimation of the inventory and vertical distribution of 137Cs in the soil. The values of 137Cs inventory in the soil ranged from 452 to 1620 kBq m-2 (mean = 904 kBq m-2, median = 964 kBq m-2). The results of the measurement of soil samples were used to calculate values of the air kerma rate, normalized to the inventory of radioactive caesium in the soil. On average, the normalized indicator of the air kerma rate from the man-made source was higher in forests (1.13 nGy h-1 per kBq m-2) compared to virgin meadows (0.95 nGy h-1 per kBq m-2). Normalized air kerma rate in cultivated meadows and vegetable gardens was approximately two times lower than the corresponding indicator for virgin meadows. Using a field gamma spectrometer-dosemeter, ambient dose equivalent rate of gamma radiation in the air was measured at the surveyed sites and the contributions of the technogenic and natural components to the dose rate were estimated. Additionally, such measurements were performed on asphalted surfaces (5 sites) and inside two wooden houses. The measured values of the total ambient dose equivalent rate at a height of 1 m above the ground, asphalted surface or house floor varied from 160 to 2260 nSv h-1. The lowest levels were recorded over asphalted surfaces and inside houses, and the highest ones at forest and virgin meadow sites. The contribution of the technogenic component to the total dose rate varied from 61.9% to 98.8% (mean = 88.9%; n = 26). The effective dose of anthropogenic radiation calculated from the results of in situ measurements in a forest, virgin meadow, cultivated meadow, kitchen garden, asphalted area and house was 0.59, 0.80, 0.34, 0.29, 0.06 and 0.06 µSv h-1, respectively. Similar values for land plots were calculated based on ex situ analysis of soil samples. It can be expected that, starting from 2020, the average effective external dose of a person staying in the resettlement zone of the Vetka district will not exceed 1 mSv year-1.

Patient doses from medical examinations in Russia: 2009-2015.

The aim of this study was to evaluate adult patient doses in Russia in the context of patient protection. Effective doses from x-ray and nuclear medicine examinations were assessed using two approaches. The first was based on data collection performed by the authors in hospitals in St. Petersburg and other 17 Russian regions. The second approach was to assess mean doses through the collective dose estimated annually within the federal data bank ESKID. In 2015, 203 million examinations were conducted in Russia, i.e. 1.4 examinations per capita. The number of examinations has increased by 35% over the last 10 years. Patient doses from x-ray examinations are strongly dependent on the imaging modality. Mean dose increases by an order of magnitude with each x-ray modality from dental examinations (0.01-0.1 mSv) to radiography (0.1-1 mSv), fluoroscopy and CT (1-10 mSv) and to interventional examinations (more than 10 mSv). Mean doses for x-ray examinations are comparable with that of foreign countries. Scintigraphy examinations with 99mTc are associated with mean doses of 1-5 mSv. Mean doses from PET/CT whole body examinations are 15-25 mSv with similar contributions from CT and radiopharmaceuticals. In nuclear medicine, patient doses are lower compared to other countries. According to ESKID data the collective dose from medical exposure in Russia has decreased from 140 000 man-Sv in 2000 to 77 000 man-Sv in 2015. Medical exposure contributes about 13% into a total collective dose. The maximum contribution was from CT examinations, i.e. 45% in 2015. A range of mean doses between different hospitals was up to two orders of magnitude for radiography and one order of magnitude for CT. In interventional studies, the scatter of individual doses was significant. Significant variations in doses between hospitals and some regions indicate the potential for optimization with the focus on interventional examinations, CT and nuclear medicine examinations combined with CT.

PROPOSALS FOR THE ESTABLISHMENT OF NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR RADIOGRAPHY FOR ADULT PATIENTS BASED ON REGIONAL DOSE SURVEYS IN RUSSIAN FEDERATION.

In 2009-2014, dose surveys aimed to collect adult patient data and parameters of most common radiographic examinations were performed in six Russian regions. Typical patient doses were estimated for the selected examinations both in entrance surface dose and in effective dose. 75%-percentiles of typical patient effective dose distributions were proposed as preliminary regional diagnostic reference levels (DRLs) for radiography. Differences between the 75%-percentiles of regional typical patient dose distributions did not exceed 30-50% for the examinations with standardized clinical protocols (skull, chest and thoracic spine) and a factor of 1.5 for other examinations. Two different approaches for establishing national DRLs were evaluated: as a 75%-percentile of a pooled regional sample of patient typical doses (pooled method) and as a median of 75%-percentiles of regional typical patient dose distributions (median method). Differences between pooled and median methods for effective dose did not exceed 20%. It was proposed to establish Russian national DRLs in effective dose using a pooled method. In addition, the local authorities were granted an opportunity to establish regional DRLs if the local radiological practice and typical patient dose distributions are significantly different.

MANAGEMENT OF PATIENT DOSES FROM DIGITAL X-RAY CHEST SCREENING EXAMINATIONS.

An anthropomorphic phantom study was carried out in 2013-14 in two hospitals, one located in Russia (Mariinsky Hospital, Saint Petersburg) and the other in Sweden (Skåne University Hospital, Malmö). The aim of the study was to investigate the possibilities to reduce the patient dose from digital X-ray chest screening examinations. The existing chest imaging protocols were adjusted by changing the tube voltage, total filtration and grid in order to determine the most dose-effective combination of the examination parameters. It was possible to achieve up to 50 % dose-area product (DAP) and 30 % effective dose reduction by raising the tube voltage from 100 to 125 or 150 kV, and simultaneously decrease the total filtration to the minimum allowed by the X-ray unit (3 mm Al). The absence of a grid allowed to further reduce the DAP and effective dose by up to 80 %. Comparison between Russian and Swedish X-ray units showed the same trend in DAP and effective dose reduction, but the absolute dose values were lower by almost a factor of 10 for the Swedish units due to different image receptors and automatic exposure control settings.

Russian practical guidance on radiological support for justification of X-ray and nuclear medicine examinations.

An important part of the justification process is assessment of the radiation risks caused by exposure of a patient during examination. The authors developed official national methodology both for medical doctors and sanitary inspectors called 'assessment of radiation risks of patients undergoing diagnostic examinations with the use of ionizing radiation'. The document addresses patients of various age groups and a wide spectrum of modern X-ray and nuclear medicine examinations. International scale of risk categorisation was implemented by the use of effective dose with account for age dependence of radiation risk. The survey of effective doses in radiology, including CT, mammography, and intervention radiology, and nuclear medicine, including single-photon emission tomography and positron emission tomography, for patients of various age groups from several regions of Russia was used for the risk assessment. The output of the methodology is a series of tables for each diagnostic technology with lists of examinations for three age groups (children/adolescents, adults and seniors) corresponding to various radiation risk categories.