Radiation Protection Dosimetry - current issue

EURADOS intercomparison 2006 to harmonise European early warning dosimetry systems

Dombrowski, H., Neumaier, S., Thompson, I. M. G., Wissmann, F. — 2009-06-30

In 2006, the European Radiation Dosimetry (EURADOS) Working Group on Environmental Radiation Monitoring (WG3) organised a third European intercomparison of dosimetry systems operated in national early warning networks. Similar to the intercomparisons in 1999 and 2002, the main aim of this exercise was to support the process of harmonisation of area monitoring in Europe by providing the network operators with basic information on the calibration and performance of their dosimetry systems. In order to characterise these systems, their following basic parameters were investigated: the response to terrestrial and cosmic radiation, the detectors' inherent background, the response at low dose rates, the energy dependence of the response as well as the sensitivity of the detector systems to small changes of the dose rate in a natural environmental radiation field. In the 2006 EURADOS intercomparison, scientists from seven countries participated to study the characteristics of 11 detector systems. All results are presented in terms of the operational quantity ambient dose equivalent, H*(10). The advent of this quantity has caused the development of new detector systems for area monitoring. Some of these new systems participated in a EURADOS intercomparison for the first time. The results are consistently presented together with uncertainties so that statistical effects can be distinguished from real detector features, which improves the interpretation of the results. By using the results of this intercomparison, some detectors were re-calibrated. The achievable improvements concerning harmonisation in dose-rate measurements in the natural environment are discussed.

Monte Carlo estimation of photoneutrons contamination from high-energy X-ray medical accelerators in treatment room and maze: a simplified model

2009-06-30

Despite all advantages associated with high-energy radiotherapy to improve therapeutic gain, the production of photoneutron via interaction of high-energy photons with high atomic number (Z) materials increases undesired dose to the patient and staff. Owing to the limitation and complication of experimental neutron dosimetry in mixed beam environment, including photon and neutron, the Monte Carlo (MC) simulation is a gold standard method for calculation of photoneutron contaminations. On the other hand, the complexity of treatment head makes the MC simulation more difficult and time-consuming. In this study, the possibility of using a simplified MC model for the simulation of treatment head has been investigated using MCNP4C general purpose MC code. As a part of comparative assessment strategy, the fluence, average energy and dose equivalent of photoneutrons were estimated and compared with other studies for several fields and energies at different points in treatment room and maze. The mean energy of photoneutrons was 0.17, 0.19 and 0.2 MeV at the patient plan for 10, 15 and 18 MeV, respectively. The calculated values differed, respectively, by a factor of 1.4, 0.7 and 0.61 compared with the reported measured data for 10, 15 and 18 MeV. Our simulation results in the maze showed that the neutron dose equivalent is attenuated by a factor of 10 for every 4.6 m of maze length while the related factor from Kersey analytical method is 5 m. The neutron dose equivalent was 4.1 mSv Gy^–1 at the isocentre and decreased to 0.79 mSv Gy^–1 at a distance of 100 cm away from the isocentre for 40 x 40 cm². There is good agreement between the data calculated using simplified model in this study and measurements. Considering the reported high uncertainties (up to 50%) in experimental neutron dosimetry, it can be concluded that the simplified model can be used as a useful tool for estimation of photoneutron contamination associated with high-energy photon radiotherapy.

Organ dose conversion coefficients for external photon irradiation using the Chinese voxel phantom (CVP)

Li, J., Qiu, R., Zhang, Z., Liu, L., Zeng, Z., Bi, L., Li, W. — 2009-06-30

A set of conversion coefficients from kerma free-in-air to the organ absorbed dose are presented for external monoenergetic photon beams from 10 keV to 10 MeV based on a whole-body, Chinese adult male voxel phantom. This computational phantom, called the Chinese voxel phantom (CVP), including totally 23 organs, was developed from magnetic resonance imaging of a young healthy Chinese man at a resolution of 2 x 2 mm. Compared with the ICRP Reference Man, more than half of the organs or tissues in the CVP show mass differences of more than 20. Monte Carlo simulations with MCNP code were carried out to calculate the organ dose conversion coefficients. Irradiation conditions include anterior–posterior, posterior–anterior (PA), right-lateral, left-lateral, rotational and isotropic geometries. Organ dose conversion coefficients from this study are compared with the data from the Asian voxel phantoms Visible Chinese Human and KORMAN. These data sets agree with each other within 10% for photon energy >5 MeV. However, discrepancies of 34–63% were observed for organs of the alimentary tract, such as the oesophagus and stomach, those of the urinary system, such as the bladder wall and thyroid, especially at low photon energy range and PA geometry. These results suggest that the anatomical variation within the Chinese population, as represented by these adult male voxel phantoms, can lead to uncertainties when a standard phantom is used for the entire population.

Study of environmental radioactivity in Palestine by in situ gamma-ray spectroscopy

Lahham, A., Al-Masri, H., Judeh, A. — 2009-06-30

This work presents qualitative and quantitative evaluation of environmental radioactivity in the central and southern areas of the West Bank, Palestine. For this purpose, the technology of in situ gamma-ray spectroscopy is used with a scintillation of 7.6 x 7.6 cm NaI(Tl) crystal connected to multichannel analyzer InSpector 2000 from Canberra instruments and laptop computer. Gamma-ray spectra were collected using the detector placed 1 m above the ground surface. Calibration of the detection system for in situ measurements of gamma-emitting radionuclides in open terrain is performed theoretically using Monte Carlo techniques. Measurements are conducted in 18 locations in 3 regions across the West Bank. The vast majority of identified radionuclides are naturally occurring gamma-emitting sources (the decay products of ²³⁸U, ²³²Th and ⁴⁰K). The only identified anthropogenic radionuclide is ¹³⁷Cs. Activity concentrations of ⁴⁰K, ²³⁸U, ²³²Th as well as the total outdoor gamma dose rate from these radionuclides were determined from the gamma-ray spectra. The highest activity concentrations of the three primordial radionuclides were 203 Bq kg^–1 for ⁴⁰K, 32 Bq kg^–1 for ²³⁸U and 30 Bq kg^–1 for ²³²Th. The total outdoor gamma dose rate calculated for the whole study area at 1 m above ground ranged from 6 to 30 nGy h^–1 with a mean of 18 ± 7 nGy h^–1, which represents about 30% of the world average value.

Mass attenuation coefficients of natural Rhizophora spp. wood for X-rays in the 15.77-25.27 keV range

Shakhreet, B. Z., Bauk, S., Tajuddin, A. A., Shukri, A. — 2009-06-30

The mass attenuation coefficients (µ/) of Rhizophora spp. were determined for photons in the energy range of 15.77–25.27 keV. This was carried out by studying the attenuation of X-ray fluorescent photons from zirconium, molybdenum, palladium, silver, indium and tin targets. The results were compared with theoretical values for average breast tissues in young-age, middle-age and old-age groups calculated using photon cross section database (XCOM), the well-known code for calculating attenuation coefficients and interaction cross-sections. The measured mass attenuation coefficients were found to be very close to the calculated XCOM values in breasts of young-age group.

Radioactivity in drilled and dug well drinking water of Ogun state Southwestern Nigeria and consequent dose estimates

Ajayi, O. S., Achuka, J. — 2009-06-30

Activity concentrations of ⁴⁰K, ²²⁶Ra, ²²⁸Ac and ²³⁵U were measured in 11 dug and 9 drilled well water samples from 3 large cities in Ogun state, Southwestern Nigeria, consumed by the population living in the cities. The measurement was done using co-axial type high-purity germanium (HPGe) detector (Canberra Industries Inc.). The measured activity concentrations in the water samples ranged from 1.74 ± 1.83 to 4.69 ± 0.17 Bq l^–1; 2.89 ± 0.62 to 7.79 ± 7.22 Bq l^–1; 0.35 ± 0.07 to 1.17 ± 0.40 Bq l^–1 and 0.18 ± 0.05 to 4.77 ± 0.34 Bq l^–1 for ⁴⁰K, ²²⁶Ra, ²²⁸Ac and ²³⁵U, respectively. Total annual effective dose rates from the ingestion of these radionuclides in the untreated wells were estimated using measured activity concentrations in the radionuclides and their ingested dose conversion factors. Estimated annual effective dose rates ranged from 0.04 to 6.82; 0.01 to 1.36 and 0.01 to 1.49 mSv y^–1 for age groups <1, 2–7 and ≥17 y, respectively. Committed dose for age group ≥17 y ranged from 8.8 x 10^–4 to 8.9 x 10^–2 Sv. The calculated annual effective dose values due to the ingestion of ²²⁶Ra in the Awujale, Ake, Saboab, Alagbon, Alapora and Totoro samples exceeded International Commission on Radiological Protection limit of 1.0 mSv y^–1 for individual public exposure. These wells are recommended for treatment that would remove radium from their waters.

Radiation exposure from radioactive iodine 131I in and surrounding the patients' room

Abu-Khaled, Y. S., Sandouqa, A. S., Haddadin, I. M. — 2009-06-30

The purpose of this study is to measure the environmental radiation exposure in and surrounding the room of patients treated with ¹³¹I. Absorbed dose rates were measured using thermoluminescence dosemeters, type TLD-200 (CaF₂:Dy), in a continuous monitoring programme. It is found that the estimated annual shallow and deep dose rates are 226 and 175 mGy at the patient bed; 94 and 72 mGy in the bathroom; and 12 and 10 mGy at the visitor chair, respectively. The annual absorbed dose in the corridor is almost at the background level. It is found that the annual doses at the patient bed and in bathroom were above the limit for radiation workers, whereas the dose rate at the visitor chair was within the accepted limit for radiation workers and above the limit for the public.