18F-choline PET/CT for parathyroid scintigraphy: significantly lower radiation exposure of patients in comparison to conventional nuclear medicine imaging approaches.

BACKGROUND: Parathyroid subtraction scintigraphy (PSS) is the most commonly used imaging method for localisation of hyperfunctioning parathyroid glands (HPGs) in primary hyperparathyroidism (PHP), a common endocrine disorder. Hybrid (SPECT/CT) imaging with 99mTc-sestaMIBI (MIBI) at an early and delayed phase (dual-phase imaging) may be the most accurate conventional imaging approach, but includes additional radiation exposure due to added CT imaging. Recently, 18F-choline (FCH) PET/CT was introduced for HPG imaging, which can also be performed using the dual-phase approach. To date, no studies have compared organ doses and the effective dose (ED) from conventional subtraction scintigraphy, dual-phase MIBI SPECT/CT, and FCH PET/CT in the localisation of HPGs. AIM: In addition to the comparison of the diagnostic performance of FCH PET/CT and conventional scintigraphic imaging methods, the aim of the study was to measure the organ doses and the ED for conventional subtraction parathyroid imaging protocols, using dual-phase MIBI SPECT/CT as a potential conventional imaging method of choice and FCH dual-phase PET/CT as a potential future imaging method of choice for the localisation of HPGs. Materials, methods. Thirty-six patients referred for parathyroid imaging with a clinical indication of PHP underwent preoperative PSS and dual-phase SPECT/CT imaging with the addition of FCH PET/CT. The diagnostic performance of the imaging modalities was assessed by using histology results as a gold standard. Radiation exposure was calculated for the administered activities of radiopharmaceuticals using ICRP80 weighting factors and for CT exposure at hybrid imaging using dose-length products and the ImPACT CT Patient Dosimetry Calculator. RESULTS: The diagnostic performance of FCH PET/CT was significantly better than that of conventional imaging modalities (sensitivity of 97% vs 64% and 46% for MIBI SPECT/CT and PSS, respectively, with comparable specificity of over 95% for all modalities). The highest radiation exposure was caused by conventional PSS (7.4 mSv), followed by dual-phase MIBI SPECT/CT (6.8 mSv). The radiation exposure was the lowest for dual-phase FCH PET/CT imaging (2.8 mSv). The added CT imaging for both hybrid approaches did not cause significant additional radiation exposure (1.4 mSv for MIBI SPECT/CT, additional 26.4% to overall exposure; 0.8 mSv for FCH PET/CT, additional 42.4% to overall exposure). CONCLUSION: In comparison to conventional scintigraphic imaging of HPGs, emerging hybrid (SPECT/CT, PET/CT) imaging techniques combine superior diagnostic performance with lower radiation exposure to patients.

Investigating the vertical and spatial extent of radon-based classification of the atmospheric mixing state and impacts on seasonal urban air quality.

A recently-developed radon-based method for combined classification of both diurnal and synoptic timescale changes in the atmospheric mixing state is applied to 1-year of observations in Ljubljana (capital of Slovenia). Five diurnal-timescale mixing classes (#1 to #5) were defined for each season along with an additional mixing class (#6) in non-summer months, representative of synoptic-timescale changes of the atmospheric mixing state associated with "persistent temperature inversion" (PTI) events. Seasonal composite radiosonde profiles and mean sea level pressure charts within each mixing class are used to demonstrate the link between prevailing synoptic conditions and the local mixing state, which drives changes in urban air quality. Diurnal cycles of selected pollutants (BC, NO2, CO, PM10, SO2 and O3) exhibited substantial seasonality as a result of changing mixing conditions, source types and strengths. For the more well-mixed conditions (classes #2 to #3), surface wind speeds were 3 times higher than during class #6 (PTI) conditions, resulting in a 3-fold reduction of primary pollutant accumulation. Daily-mean PM10 concentrations only exceeded EU and WHO guideline values in winter and autumn for two of the radon-defined mixing classes: (i) class #5 (strongly stable near-surface conditions associated with passing synoptic anti-cyclone systems), and (ii) class #6 (PTI conditions driven by regional subsidence in the presence of the "Siberian High"). Both mixing states were associated with low mean wind speeds (∼0-0.7 m s-1) and strong thermal stratification, as indicated both by pseudo-vertical temperature gradients (∆T/∆z) and radiosonde profiles. Diurnal ∆T/∆z values indicated limited opportunity for convective mixing of pollutants from the basin atmosphere under these conditions. The demonstrated consistency in atmospheric mixing conditions (vertically and spatially) across the diurnal cycle within each of the defined mixing classes suggests the radon-based classification scheme used in conjunction with 3-D urban sensor networks could be well suited to evaluate mitigation schemes for urban pollution and urban climate.

Prokaryotic and eukaryotic airborne microorganisms as tracers of microclimatic changes in the underground (Postojna Cave, Slovenia).

Bioaerosols in cave air can serve as natural tracers and, together with physical parameters, give a detailed view of conditions in the cave atmosphere and responses to climatic changes. Airborne microbes in the Postojna Cave system indicated very dynamic atmospheric conditions, especially in the transitory seasonal periods between winter and summer. Physical parameters of cave atmosphere explained the highest variance in structure of microbial community in the winter and in the summer. The airborne microbial community is composed of different microbial groups with generally low abundances. At sites with elevated organic input, occasional high concentrations of bacteria and fungi can be expected of up to 1,000 colony-forming units/m(3) per individual group. The most abundant group of airborne amoebozoans were the mycetozoans. Along with movements of air masses, airborne algae also travel deep underground. In a cave passage with elevated radon concentration (up to 60 kBq/m(3)) airborne biota were less abundant; however, the concentration of DNA in the air was comparable to that in other parts of the cave. Due to seasonal natural air inflow, high concentrations of biological and inanimate particles are introduced underground. Sedimentation of airborne allochthonous material might represent an important and continuous source of organic material for cave fauna.

Analysis of Ventilation Efficiency as Simultaneous Control of Radon and Carbon Dioxide Levels in Indoor Air Applying Transient Modelling.

The impact of ventilation efficiency on radon (222Rn) and carbon dioxide (CO2) concentrations in the indoor air of a residential building was studied by applying transient data analysis within the CONTAM 3.4 program. Continuous measurements of 222Rn and CO2 concentrations, together with basic meteorological parameters, were carried out in an apartment (floor area about 27 m2) located in Ljubljana, Slovenia. Throughout the experiment (October 3-15), frequent ventilation (several times per day), poor ventilation (once to twice per day) and no ventilation scenarios were applied, and the exact ventilation and occupancy schedule were recorded. Based on the measurements, a transient simulation of 222Rn and CO2 concentrations was performed for six sets of scenarios, where the design ventilation rate (DVR) varied based on the ventilation requirements and recommendations. On the days of frequent ventilation, a moderate correlation between the measured and simulated concentrations (r = 0.62 for 222Rn, r = 0.55 for CO2) was found. The results of the simulation indicated the following optimal DVRs: (i) 36.6 m3 h-1 (0.5 air changes per hour, ACH) to ensure a CO2 concentration below 1000 ppm and a 222Rn concentration below 100 Bq m-3; and (ii) 46.9 m3 h-1 (0.7 ACH) to ensure a CO2 concentration below 800 ppm. These levels are the most compatible with the 5C_Cat I (category I of indoor environmental quality, defined by EN 16798-1:2019) scenario, which resulted in concentrations of 656 ± 121 ppm for CO2 and 57 ± 13 Bq m-3 for 222Rn. The approach presented is applicable to various types of residential buildings with high overcrowding rates, where a sufficient amount of air volume to achieve category I indoor environmental quality has to be provided. Lower CO2 and 222Rn concentrations indoors minimise health risk, which is especially important for protecting sensitive and fragile occupants.

Determination of optimal ventilation rates in educational environment in terms of radon dosimetry.

INTRODUCTION: New and renovated energy efficient buildings with minimised ventilation rates together with increased building airtightness are often associated with higher indoor radon concentrations compared to the concentrations in existing buildings. The purpose of our study is to analyse the problem associated with the increased radon concentration and ventilation requirements and recommendations in schools. The radon concentration was critically assessed by varying the design ventilation rates (DVRs) within fifteen cases according to legislative requirements and recommendations. The case study is a branch primary school in western part of Slovenia situated in a radon prone area. METHODS: Radon (222Rn) concentrations were simulated in the classroom, using CONTAM 3.2. PROGRAM: For validation, measurements were performed on 8 measuring days in September and 6 measuring days in March. The simulated and measured 222Rn concentrations are well correlated for all measurement days, with the simulated/measured ratio of 0.85-1.39. In order to define optimal DVRs in terms of dosimetry, the effective dose and its ratio to the worldwide average effective dose at workplace, received by radon progeny in 950 h (expected effective dose, 0.13 mSv/y), were calculated for each case. RESULTS: Simulations showed that the highest radon concentrations were observed in case 1 with a DVR of 79.6 m3/h (621 Bq/m3) and case 4 with a DVR of 69.4 m3/h (711 Bq/m3), both defined by national regulations. The calculated values in both cases exceeded the national reference value for radon (300 Bq/m3) by 2.1 times and 2.4 times, and the WHO guideline value (100 Bq/m3) by 6.2 times and 7.1 times, respectively. The simulations are in line with the results of radon dosimetry. Both DVRs correspond to the highest effective doses, 1.88 mSv/y (about 14-fold higher than expected effective dose) for case 1 and 2.15 mSv/y (about 17-fold higher than expected effective dose) for case 4. Case 11_Cat I with a DVR of 1999.7 m3/h defined by EN 15251: 2007 resulted in minimal Rn concentration (35 Bq/m3) and corresponds to the lowest effective dose 0.11 mSv/y and its ratio to the expected effective dose 0.8. CONCLUSIONS: Ventilation is an immediate measure to reduce radon concentration in a classroom and it must be performed in line with other holistic measures to prevent and control radon as a health risk factor.

Tracing the sources of gaseous components (222Rn, CO2 and its carbon isotopes) in soil air under a cool-deciduous stand in Sapporo, Japan.

Radon ((222)Rn) and carbon dioxide were monitored simultaneously in soil air under a cool-temperate deciduous stand on the campus of Hokkaido University, Sapporo, Japan. Both (222)Rn and CO(2) concentrations in soil air varied with atmospheric (soil) temperature in three seasons, except for winter when the temperature in soil air remained constant at 2-3 degrees C at depth of 80 cm. In winter, the gaseous components were influenced by low-pressure region passing through the observation site when the ground surface was covered with snow of ~1 m thickness. Carbon isotopic analyses of CO(2) suggested that CO(2) in soil air may result from mixing of atmospheric air and soil components of different origins, i.e. CO(2) from contemporary soil organic matter and old carbon from deeper source, to varying degrees, depending on seasonal meteorological and thus biological conditions.

EFFECTIVE DOSES DUE TO OUTDOOR AND INDOOR RADON AT A MEDITERRANEAN SITE.

A year-long continuous measurement of the radon activity concentration in the outdoor air at a Mediterranean site has shown a range of 2-144 Bq m-3 and annual mean of 18 ± 14 Bq m-3. Seasonal means were: 15 ± 10 Bq m-3 in winter, 15 ± 12 Bq m-3 in spring, 22 ± 19 Bq m-3 in summer and 17 ± 12 Bq m-3 in autumn. In summer, the average radon activity concentration in the daytime (6-22 h) was 15.2 Bq m-3 and in the night-time (22-6 h) 33.4 Bq m-3. The annual effective dose was 1.83 mSv, with 1.66 mSv from indoor and 0.17 mSv (9%) from outdoor radon. The related doses for the summertime were (mSv): 0.29, 0.24 and 0.05 (18%).

Radon-based atmospheric stability classification in contrasting sub-Alpine and sub-Mediterranean environments.

A recently-developed radon-based technique is used to investigate relative changes in summertime atmospheric stability at two sites in Slovenia with contrasting geographical settings. Although atmospheric stability for both sites (50 km apart) was shown to be governed by similar synoptic conditions, their contrasting settings caused differences in mixing conditions for each stability category. At the urban sub-Alpine site Ljubljana, situated within a topographic basin, wind speeds associated with the most stable conditions were 0.2-0.3 m s-1. By comparison, corresponding wind speeds for the near-coastal sub-Mediterranean site Ajdovscina, located at the foothills of the Trnovski gozd barrier, were 0-0.2 m s-1. The wind direction at Ljubljana under stable conditions (∼80°) was consistent with drainage flow into the basin along the Sava River valley. The corresponding wind direction at Ajdovscina was 20-40°, consistent with gentle katabatic drainage from the flanks of the Trnovski gozd barrier. After removing fetch effects on radon variability at each site, a large contrast in local contributions to the radon signal was noted: the diurnal amplitude of the local radon signal increased from ∼24 Bq m-3 at Ljubljana to ∼47 Bq m-3 at Ajdovscina. This difference was attributed to a greater nocturnal radon accumulation rate at Ajdovscina (3.5 Bq m-3 h-1 vs 2.1 Bq m-3 h-1) due to higher radon fluxes from flysch and carbonate rocks compared to the sea and lake sediments in the Ljubljana Basin. The ability of radon to consistently distinguish subtle changes in atmospheric mixing at sites with contrasting topographic settings indicates that it will be a powerful tool for characterising air quality in these complex environments. Specifically, diurnal radon cycles indicate that the capability of the atmosphere to dilute primary pollutants is considerably less in the basin environment.

OCCUPATIONAL EXPOSURE ASSESSMENT AT A THERAPEUTIC RADON SPA FACILITY IN HUNGARY.

In order to estimate occupational exposure of workers in a therapeutic radon spa facility, radon concentration in the workplace air was investigated at Markhot Ferenc Hospital, Eger, Hungary. The investigated balneotherapeutic facility and its natural hot spa water are used for treatments and rehabilitations of rheumatic patients. Radon concentration, radon decay products at a bathhouse, treatment rooms and a consultation room were continuously measured in August and September 2018. In the present study, different levels of radon concentration among the observation sites and its clear temporal variations were found, though radon concentrations in the investigated sites were below 300 Bq m-3. Regarding such radon fluctuation and low equilibrium factor level (0.1), the annual effective doses of workers are estimated to be around 0.5 mSv year-1.

EFFECTIVE DOSES ESTIMATED FROM THE RESULTS OF DIRECT RADON AND THORON PROGENY SENSORS (DRPS/DTPS), EXPOSED IN SELECTED REGIONS OF BALKANS.

The main contribution to population exposure is due to radon and thoron progenies and not radon itself. The aim of this study was therefore to estimate annual effective dose using the results of Direct Radon and Thoron Progeny Sensors were exposed in 69 selected schools and 319 dwellings in several regions of Balkans: in Serbia: regions of Sokobanja and Kosovo and Metohija, Republic of Macedonia, Republic of Srpska and Slovenia. Obtained average total effective doses are in the range from 0.22 mSv a-1 (schools in Republic of Srpska) to 2.5 mSv a-1 (dwellings in Kosovo) and are below the reference level of 10 mSv a-1 recommended by International Commission on Radiological Protection.

Nanosize radon short-lived decay products in the air of the Postojna Cave.

At two points in the Postojna Cave, short-term monitoring in summer and in winter of air concentrations of radon and radon decay products, equilibrium factor, unattached fraction of radon decay products (f(un)), barometric pressure, relative air humidity in the cave and air temperature in the cave and outdoor has been carried out, with the emphasis on f(un). Dose conversion factors, calculated on the basis of f(un) values obtained (ranging from 0.09 to 0.65) exceed 5 mSv WLM(-1), by a factor of 11.5-14.0 in summer and of 3.0-4.0 in winter for mouth breathing, and 3.1-3.5 in summer and 1.5-1.7 in winter for nasal breathing.

Dissolved radon and gaseous mercury in the Mediterranean seawater.

Vertical profiles of radioactive radon gas ((222)Rn) and dissolved gaseous mercury (DGM) in seawater in the Mediterranean Basin have been measured. They were found in the range 1.7-19.3 Bq m(-3) and 22-200 ng m(-3), respectively, at the bottom and 2.0-20.0 Bq m(-3) and 6-80 ng m(-3), respectively, at the surface. Preliminary results indicate a positive correlation between concentrations of both gases at some locations, but not at others. Further analyses will be performed, after (226)Ra contents in sediment and water have been determined, taking into account environmental parameters such as air and water temperatures, barometric pressure and water flow, in order to better interpret these profiles.

Levels of nanosize radon decay products in indoor air: a comparison for different environments.

The fraction of unattached (fun) nanosized 222Rn short-lived decay products in indoor air has been measured in different environments and the following ranges obtained: 0.03-0.25 in kindergartens, 0.03-0.18 in schools, 0.08-0.20 in wineries, and 0.12-0.68 in a karst cave. The dependence of fun on the environmental conditions (air temperature, relative humidity and pressure), as well as on the working regime has been studied and will be discussed. Applying the dosimetric approach, dose conversion factors were calculated, based on the measured fun values, and compared to the values, obtained from epidemiological studies and currently recommended to be used in radon dosimetry.

Radon concentration in thermal water as an indicator of seismic activity.

Radon concentration in thermal springs at Hotavlje and Bled has been measured from October 2005 to June 2008 and from October 2005 to September 2007, respectively. At both locations several anomalies in radon concentration were observed, that might have been caused by seismic events. In this study all earthquakes with ratio (D/R) between strain radius (D) and distance to the epicenter (R) greater than 0.5 were taken into account. Five earthquakes occurred in the vicinity of Bled in this period, the strongest at a distance of 17 km with the magnitude ML=3.8 and four radon anomalies were observed. At Hotavlje fourteen earthquakes occurred in the vicinity with D/R ratio from 0.5 to 2.9. During this period three radon anomalies were observed.

Nano-size radon short-lived progeny aerosols in Slovenian kindergartens in wintertime.

Indoor air concentrations of radon and radon short-lived decay products, equilibrium factors, unattached fractions of radon short-lived decay products (f(un)), relative humidity, and temperature have been measured in 29 rooms of 13 Slovenian kindergartens, with an emphasis on f(un) as a crucial parameter in dose assessment. Dose conversion factors, based on the measured f(un) values were compared to epidemiology-based value of 5 mSv WLM(-1).

Comparison of radon doses based on different radon monitoring approaches.

In 43 places (23 schools, 3 kindergartens, 16 offices and one dwelling), indoor radon has been monitored as an intercomparison experiment, using α-scintillation cells (SC - Jozef Stefan Institute, Slovenia), various kinds of solid state nuclear track detectors (KfK - Karlsruhe Institute of Technology, Germany; UFO - National Institute of Radiological Sciences, Chiba, Japan; RET - University College Dublin, Ireland) and active electronic devices (EQF, Sarad, Germany). At the same place, the radon levels and, consequently, the effective doses obtained with different radon devices differed substantially (by a factor of 2 or more), and no regularity was observed as regards which detector would show a higher or lower dose.

Thoron, radon and air ions spatial distribution in indoor air.

Spatial distribution of radioactive gasses thoron (Tn) and radon (Rn) in indoor air of 9 houses mostly during winter period of 2013 has been studied. According to properties of alpha decay of both elements, air ionization was also measured. Simultaneous continual measurements using three Rn/Tn and three air-ion active instruments deployed on to three different distances from the wall surface have shown various outcomes. It has turned out that Tn and air ions concentrations decrease with the distance increase, while Rn remained uniformly distributed. Exponential fittings function for Tn variation with distance was used for the diffusion length and constant as well as the exhalation rate determination. The obtained values were similar with experimental data reported in the literature. Concentrations of air ions were found to be in relation with Rn and obvious, but to a lesser extent, with Tn.

Meteorological parameters contributing to variability in 222Rn activity concentrations in soil gas at a site in Sapporo, Japan.

Continuous (222)Rn monitoring in soil gas since November 22, 2004 has revealed variability in activity concentration with time in the semi-natural woods on the campus of Hokkaido University in Sapporo, Japan. Among various factors affecting soil radon levels and variability, temperature was found to be dominant during three seasons when activity concentrations of (222)Rn showed a diurnal high and nocturnal low with a boundary around 10 o'clock in the morning. This pattern was disturbed by low pressure fronts with occasional rain. The activity gradually decreased as soil temperatures decreased from late November to mid-December. After the ground surface was completely covered with snow, soil radon levels became low with a small fluctuation. There were several peaks of (222)Rn on the time-series chart in winter. Those peaks appearing in early winter and early spring may be interpreted by considering meteorological parameters. In a few cases, the radon activity suddenly increased with increasing pressure in the soil at a depth of 10 cm, which may be associated with subsurface events such as seismic activity in the area.

Radon survey and exposure assessment in hospitals.

In this study radon (222Rn) in indoor air was surveyed in 201 rooms of 26 major hospitals in Slovenia and annual effective doses for 1025 persons working in the rooms surveyed were estimated. Instantaneous radon concentrations were measured with alpha scintillation cells, long-term average concentrations with etched track detectors and electret detectors, and radon, its progeny and equilibrium factor were continuously recorded with portable devices. Effective doses were estimated by using ICRP Publication 65 methodology. Only in seven rooms did the average radon concentration, obtained by 1 month exposing etched track detectors, exceed the national limit of 400 Bq m-3; and these places will be mitigated; elsewhere it was lower. Annual effective doses for 966 persons (94.2%) were estimated as <1 mSv, but for 10 persons they were between 2.1 and 7.3 mSv. The results warn that in an environment with generally low radon levels, 'hot' points may be found, and therefore radon surveys should be carefully designed and performed in order not to miss them.

Indoor air radon concentration in schools in Prizren, Kosovo.

Indoor air radon ((222)Rn) concentrations were measured in spring and winter in 30 rooms of 9 elementary schools and 19 rooms of 6 high schools in Prizren, Kosovo, using alpha scintillation cells. Only in three rooms of elementary schools and four rooms of high schools did winter concentrations exceed 400 Bq m(-3).