Average Effective Dose Rate Research Articles

Exposure to indoor radon and natural gamma radiation in public workplaces in north-western Greece

Abstract Measurements of indoor radon levels and gamma dose rates were performed in 42 workplaces in Ioannina, north-western Greece. Radon concentrations followed a log-normal distribution with an arithmetic mean of 95 ± 51 Bq m −3 . In all cases, radon levels were below 400 Bq m −3 , which is the action level implemented by the Greek Regulation for Radiation Protection, in accordance with the European Commission recommendation. Comparing summer and winter measurements, no statistically significant seasonal variation was established. However, radon concentrations measured in basement and ground floor workplaces were significantly higher ( p −1 with a mean value of 0.62 mSv y −1 . Indoor exposure to natural gamma radiation entailed an average effective dose rate of 0.13 mSv y −1 , of which approximately 62% was due to terrestrial and the rest due to cosmic sources. The reported data contribute to the assessment of radon distribution and dose estimate at the national level.

SU‐FF‐T‐132: Efficiency of Respiratory‐Gated Synchrotron Based Scanning Beam Delivery of Proton Therapy for Lung

Purpose: To quantify the efficiency of respiratory‐gated synchrotron based scanning beam delivery of proton irradiation for lung tumors. Method and Materials: An in‐house software program was developed to simulate the interaction of the respiratory‐gate signal based on respiratory traces of patients from an external respiratory monitor and the synchrotron magnet operation pattern in scanning beam proton delivery. A simulation study was performed using 10 proton scanning beam plans (total 33 beam angles) for lung tumors. For each plan, 10 patient breathing traces were used to simulate respiratory gated delivery. The total time to deliver each beam was determined for non‐gated and gated modes (30%, 20% and 10 % duty cycles respectively). Efficiency was determined using the effective dose rate (MU/min). The relationship between effective dose rate with and without gating was examined for different irradiated volumes along each beam direction and the number of control points in each plan. Results: The average effective dose rate was 34.2±18.8 (MU/min) for non‐gated treatment. This represented an approximately three fold reduction as compared to the passively‐scattered proton delivery (90.1 MU/min). With gating, effective dose ratios were further reduced to 13.8±4.7, 9.3±3.6 and 3.7±1.7 MU/min for 30%, 20% and 10 % duty cycles respectively. Using an average MU per beam at 70.9, the estimated treatment delivery time for a single beam was 2.1 min for non‐gated treatment, and 5.1, 7.6, and 19.1 min for gated treatment with 30%, 20% and 10 % duty cycles, respectively. No strong relationship was found between the effective dose rate and the irradiated volume or the number of control points. Conclusion: Respiratory gated delivery of pulsed scanning beam proton therapy for lung cancer is less efficient than passively‐scattered proton irradiation. Further studies are needed to improve delivery efficiency in the treatment plan optimization using patient specific breathing patterns.

Assessment of external and internal doses due to farming in high background radiation areas in old tin mining localities in Jos-plateau, Nigeria

Farming on soils situated in high background radiation areas can result to enhanced radiation exposure scenarios and pathways to humans. To assess the likely levels of exposures, farm soil samples were collected from different farmlands in three old tin mining localities (Bitsichi, Bukuru and Ropp) in Jos Plateau Nigeria, known for high radiations. The soil samples were analyzed for the activity concentrations of 226 Ra, 232 Th and 40 K, using gamma-ray spectroscopy. The outdoor annual effective dose rates were calculated using the activity concentrations of the radionuclides and were found to vary from 0.07 mSv to 2.02 mSv across the three localities. Considering dust generation from soil tillage and inadvertent ingestion of soil particles, the likely internal radiation hazards were estimated using conservative dust and soil loading factors. The total average annual effective dose rates due to 226 Ra and 232 Th that could result from dust inhalation and ingestion of soil particles were 16.9 µSv, 8.1 µSv and 8.8 µSv, respectively for Bitsichi, Bukuru and Ropp. Though these values are about 5% the outdoor exposures to the farmers in those farms and greater than 1 µSv y-1 , from the point of view of radiation protection and risk, they are significant. It suffices to say, therefore, that the results of this study will create the possibility of the importance to evaluate the health risk among the farming population and workplace environments which often is not covered by regulations concerning health protection.

Radionuclide contents and physico-chemical characterization of solid waste and effluent samples of some selected industries in the city of Lagos, Nigeria

The radionuclide contents in waste products and physico-chemical characterization of effluent samples from some selected industries in the city of Lagos were carried out. The radioactivity concentration levels due to 40 K, 226 Ra and 228 Th in the solid wastes were determined using gamma-ray spectrometry while physico-chemical determination of parameters were based on standard methods of measurements. The average radioactivity levels obtained was between 104 ± 14 Bq kg -1 and 1276 ± 31 Bq kg -1 for 40 K, 86 ± 18 Bq kg -1 and 122 ± 23 Bq kg -1 for 226 Ra and while for 228 Th it ranged between 14 ± 2 Bq kg -1 and 73 ± 10 Bq kg -1 . No artificial radioactive elements were detected in any of the samples. The average outdoor effective dose rate due to gamma exposure from these waste materials in the city was calculated as 0.12 mSv y -1 . This is far less than 1 mSv y -1 recommended limit for the member of the public by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The pH of the effluent samples was slightly alkaline, while the electrical conductivity ranged between 275 and 455 µS cm -1 and total suspended solids ranged from 104 to 5616 mg l -1 . All these ranges and those of biochemical and chemical oxygen demand values were all higher than the prescribed limits. Presence of heavy metals in the effluent samples was however lower than prescribed with the exception of iron.

Natural radiation doses for cosmic and terrestrial components in Costa Rica

A study of external natural radiation, cosmic and terrestrial components, was carried out with in situ measurements using NaI scintillation counters while driving along the roads in Costa Rica for the period July 2003–July 2005. The geographical distribution of the terrestrial air-absorbed dose rates and the total effective dose rates (including cosmic) are represented on contour maps. Information on the population density of the country permitted the calculation of the per capita doses. The average effective dose for the total cosmic component was 46.88±18.06 nSv h −1 and the average air-absorbed dose for the terrestrial component was 29.52±14.46 nGy h −1. The average total effective dose rate (cosmic plus terrestrial components) was 0.60±0.18 mSv per year. The effective dose rate per capita was found to be 83.97 nSv h −1 which gives an annual dose of 0.74 mSv. Assuming the world average for the internal radiation component, the natural radiation dose for Costa Rica will be 2.29 mSv annually.

Radiological impacts of the amang processing industry on neighbouring residents

The processing of amang (one of a number of tin-tailing products) for its valuable minerals has associated with the radiological and environmental problems. The processing and stockpiling of amang and ilmenite in open-air spaces, subject as it is to environmental influences, gives rise to a potential for affecting residents in adjacent area. A case study was carried out in a residential area neighbouring a typical amang plant to investigate the radiological impact to the residents. The average Effective Dose rates, calculated based on the contributions of Effective Dose rates from inhaled suspended radioactive dust, radon–thoron and their progeny, and external gamma radiation, were determined for selected houses. Results show that the occupants of those houses received Effective Dose rate, which cannot be differentiated from background. The major contributor to the average Effective Dose rate came from external radiation sources. Inhaled radon and its progeny was the second major contributor.

137Cs exposure in the Marshallese populations: an assessment based on whole-body counting measurements (1989-1994).

The Marshall Islands were the site of numerous tests of nuclear weapons by the United States. From 1946 to 1958, nuclear devices were detonated at Enewetak and Bikini Atolls. Following the inadvertent contamination of the northern islands downwind of the 1954 Bravo Test, Brookhaven National Laboratory became involved in the medical care and the radiological safety of the affected populations. One important technique employed in assessing the internally deposited radionuclides is whole-body counting. To estimate current and future exposures to 137Cs, data from 1989 to 1994 were analyzed and are reported in this paper. During this period, 3,618 measurements were made for the Marshallese. The cesium body contents were assumed to result from a series of chronic intakes. Also, it was assumed that cesium activity in the body reaches a plateau that is maintained over 365 d. We estimated the annual effective dose rate for each population, derived from the recommendations of the International Commission on Radiological Protection. The average 137Cs uptake measured by the whole-body counting method varies from one population to another; it was consistent with measurements of external exposure rate. The analysis, though based on limited data, indicates that there is no statistical support for a seasonal effect on 137Cs uptake. The critical population group for cesium uptake is adult males. Within the 5-y monitoring period, all internal exposures to 137Cs were less than 0.2 mSv y(-1). Similarly, a persistent average cesium effective dose rate of 2 microSv y(-1) was determined for Majuro residents.

Outdoor Radon Dose Conversion Coefficient in South-Western and South-Eastern United States

Two hundred and forty samples of radon ( 222 Rn) gas concentration, together with unattached and attached-to-ambient-aerosol radon progeny concentrations, were collected at 16 outdoor sites in four US states. The effective dose rate (to the lungs) was calculated with ICRP's recently recommended lung dosimetry model (ICRP Publication 66) using the measured potential alpha energy concentration (PAEC) and unattached fraction (f P ). The measurement procedure for f P assumed a characteristic particle diameter of 1.1 nm for the unattached progeny. The site-average value of the conversion coefficient between radon gas concentration and effective dose rate was found to be 6.7 nSv.h -1 per Bq.m -3 , with a standard deviation of 1.3 nSv.h -1 per Bq.m -3 . The correlation coefficient (r) of effective dose rate with respect to radon gas concentration between these 16 sites was 0.98. Thus, the radon gas concentration alone was a good predictor of effective dose rate in outdoor air, at least when the dose calculation was based on a known PAEC and the assumption of discrete unattached and attached particle size modes. For an average outdoor occupancy of 5 h.d -1 together with the average radon gas concentration, the annual effective dose rate averaged for outdoor exposure at these 16 sites was approximately 80 μSv.y -1 , with a median value of 54 μSv.y -1 and a geometric standard deviation between sites of about 1.9. The average effective dose rate from outdoor radon progeny found in this study is approximately one-tenth the value of 740 μSv.y -1 from indoor exposure, which is based on the EPA's value of 46.3 Bq.m -3 for the average radon gas concentration in US homes, and ICRP's recommended dose conversion convention of 1.1 mSv per mJ.h.m -3 (3.8 msv.WLM -1 ). Correlations between the outdoor dose rate and a number of meteorological and environmental variables were examined : equivalent uranium concentration in soils, wind speed, terrain roughn

Effective dose to patients due to fluoroscopic screening in barium meal examinations: comparison between free and restricted X-ray beams

Four complete barium meal (BM) fluoroscopic examinations were digitised as sequences of 160 × 128 pixel, 8 bit images, at a rate of about 100 per min using a computer frame-grabber system and were recorded on disk for processing. The images were latter replayed and, using a suitable program, were superimposed in a new picture so that anatomic details coincided. At the same time, two more pictures were created by summing the radiation fields corresponding to the images grabbed, one with open diaphragms at 26 × 22 cm field size and one with simulated closed diaphragms at 7 × 11 cm. The average effective dose rate delivered to the patient during fluoroscopic screening was calculated for a hermaphrodite mathematical phantom and was found to be 0.21 mSv/min and 0.005 mSv/min, respectively, if either technique had been used exclusively. The average effective dose delivered to the patients with the actual techniques used in the 4 BM examinations recorded was 0.394 mSv. Data from these examinations was extrapolated to a sample group of 122 BM examinations, performed during a 9-week period, for which total exposure duration was known. The average effective dose calculated for fluoroscopy was shown to be negligible, particularly if only the ‘closed’ diaphragm technique was used, when compared to the estimated average effective dose of about 8.6 mSv delivered by the radiographs made during each examination.