X. Ortega

Thermoluminescence dosimetry applied to in vivo dose measurements for total body irradiation techniques

BACKGROUND AND PURPOSE In total body irradiation (TBI) treatments in vivo dosimetry is recommended because it makes it possible to ensure the accuracy and quality control of dose delivery. The aim of this work is to set up an in vivo thermoluminescence dosimetry (TLD) system to measure the dose distribution during the TBI technique used prior to bone marrow transplant. Some technical problems due to the presence of lung shielding blocks are discussed. MATERIALS AND METHODS Irradiations were performed in the Hospital de la Santa Creu i Sant Pau by means of a Varian Clinac-1800 linear accelerator with 18 MV X-ray beams. Different TLD calibration experiments were set up to optimize in vivo dose assessment and to analyze the influence on dose measurement of shielding blocks. An algorithm to estimate midplane doses from entrance and exit doses is proposed and the estimated dose in critical organs is compared to internal dose measurements performed in an Alderson anthropomorphic phantom. RESULTS The predictions of the dose algorithm, even in heterogeneous zones of the body such as the lungs, are in good agreement with the experimental results obtained with and without shielding blocks. The differences between measured and predicted values are in all cases lower than 2%. CONCLUSIONS The TLD system described in this work has been proven to be appropriate for in vivo dosimetry in TBI irradiations. The described calibration experiments point out the difficulty of calibrating an in vivo dosimetry system when lung shielding blocks are used.

Natural and anthropogenic radionuclides in airborne particulate samples collected in Barcelona (Spain)

Results for naturally occurring (7)Be, (210)Pb, (40)K, (214)Bi, (214)Pb, (212)Pb, (228)Ac and (208)Tl and anthropogenic (137)Cs in airborne particulate matter in the Barcelona area during the period from January 2001 to December 2005 are presented and discussed. The (212)Pb and (208)Tl, (214)Bi and (214)Pb, (7)Be and (210)Pb radionuclide levels showed a significant correlation with each other, with correlation coefficients of 0.99, 0.78 and 0.69, respectively, suggesting similar origin/behaviour of these radionuclides in the air. Caessium-137 and Potassium-40 were transported to the air as resuspended particle from the soil. The (7)Be and (210)Pb concentrations showed similar seasonal variations, with a tendency for maximum concentrations during the summer months. An inverse relationship was observed between the (7)Be, (210)Pb, (40)K and (137)Cs concentrations and weekly rainfall, indicating washout of atmospheric aerosols carrying these radionuclides.

Monte Carlo simulation of MOSFET detectors for high-energy photon beams using the PENELOPE code.

The aim of this work was the Monte Carlo (MC) simulation of the response of commercially available dosimeters based on metal oxide semiconductor field effect transistors (MOSFETs) for radiotherapeutic photon beams using the PENELOPE code. The studied Thomson&Nielsen TN-502-RD MOSFETs have a very small sensitive area of 0.04 mm(2) and a thickness of 0.5 microm which is placed on a flat kapton base and covered by a rounded layer of black epoxy resin. The influence of different metallic and Plastic water build-up caps, together with the orientation of the detector have been investigated for the specific application of MOSFET detectors for entrance in vivo dosimetry. Additionally, the energy dependence of MOSFET detectors for different high-energy photon beams (with energy >1.25 MeV) has been calculated. Calculations were carried out for simulated 6 MV and 18 MV x-ray beams generated by a Varian Clinac 1800 linear accelerator, a Co-60 photon beam from a Theratron 780 unit, and monoenergetic photon beams ranging from 2 MeV to 10 MeV. The results of the validation of the simulated photon beams show that the average difference between MC results and reference data is negligible, within 0.3%. MC simulated results of the effect of the build-up caps on the MOSFET response are in good agreement with experimental measurements, within the uncertainties. In particular, for the 18 MV photon beam the response of the detectors under a tungsten cap is 48% higher than for a 2 cm Plastic water cap and approximately 26% higher when a brass cap is used. This effect is demonstrated to be caused by positron production in the build-up caps of higher atomic number. This work also shows that the MOSFET detectors produce a higher signal when their rounded side is facing the beam (up to 6%) and that there is a significant variation (up to 50%) in the response of the MOSFET for photon energies in the studied energy range. All the results have shown that the PENELOPE code system can successfully reproduce the response of a detector with such a small active area.

Natural radioactivity in drinking water in Catalonia (Spain)

A survey to study natural radioactivity in drinking water was carried out in Catalonia (northeast Spain). Approximately 800 samples of drinking water were analysed between 1986 and 1993. The samples were categorized according to origin: bottled or public supply. The samples were analysed for gross alpha, gross beta, 234U, 235U, 238U, 226Ra, 228Ra, 230Th, 232Th, 210Pb, and 210Po activity. The activity concentration for gross alpha was found to range from 0.02 to 1.75 Bq/L and for gross beta from 0.04 to 2.9 Bq/L. The gross beta activity content in the majority of the samples is due to 40K. Average concentrations of 234U, 238U, 226Ra, and 210Pb in the waters studied ranged from 10 to 100 mBq/L. Concentrations of 700 mBq/L were obtained for 234U, 960 mBq/L for226 Ra, and 1130 mBq/L for 210Pb. The highest levels of alpha radioactivity are due to the presence of granitic formations in the region. A high degree of radioactive disequilibrium was noted among members of the uranium series present in some samples of water. The 234U238U activity ratio varied between 1 and 4, and the waters with the lowest uranium activity registered the highest level of 234U238U activity ratio.

Extremity exposure in nuclear medicine: preliminary results of a European study.

The Work Package 4 of the ORAMED project, a collaborative project (2008-11) supported by the European Commission within its seventh Framework Programme, is concerned with the optimisation of the extremity dosimetry of medical staff in nuclear medicine. To evaluate the extremity doses and dose distributions across the hands of medical staff working in nuclear medicine departments, an extensive measurement programme has been started in 32 nuclear medicine departments in Europe. This was done using a standard protocol recording all relevant information for radiation exposure, i.e. radiation protection devices and tools. This study shows the preliminary results obtained for this measurement campaign. For diagnostic purposes, the two most-used radionuclides were considered: (99m)Tc and (18)F. For therapeutic treatments, Zevalin(®) and DOTATOC (both labelled with (90)Y) were chosen. Large variations of doses were observed across the hands depending on different parameters. Furthermore, this study highlights the importance of the positioning of the extremity dosemeter for a correct estimate of the maximum skin doses.

Distribution of uranium isotopes in surface water of the Llobregat river basin (Northeast Spain).

A study is presented on the distribution of (234)U, (238)U, (235)U isotopes in surface water of the Llobregat river basin (Northeast Spain), from 2001 to 2006. Sixty-six superficial water samples were collected at 16 points distributed throughout the Llobregat river basin. Uranium isotopes were measured by alpha spectrometry (PIPS detectors). The test procedure was validated according to the quality requirements of the ISO17025 standard. The activity concentration for the total dissolved uranium ranges from 20 to 261mBqL(-1). The highest concentrations of uranium were detected in an area with formations of sedimentary rock, limestone and lignite. A high degree of radioactive disequilibrium was noted among the uranium isotopes. The (234)U/(238)U activity ratio varied between 1.1 and 1.9 and the waters with the lowest uranium activity registered the highest level of (234)U/(238)U activity ratio. Correlations between uranium activity in the tested water and chemical and physical characteristics of the aquifer were found.

Analysis of outdoor radon progeny concentration measured at the Spanish radioactive aerosol automatic monitoring network

An analysis of 10-year radon progeny data, provided by the Spanish automatic radiological surveillance network, in relation to meteorology is presented. Results show great spatial variability depending mainly on the station location and thus, the surrounding radon exhalation rate. Hourly averages show the typical diurnal cycle with an early morning maximum and a minimum at noon, except for one mountain station, which shows an inverse behaviour. Monthly averaged values show lower concentrations during months with higher atmospheric instability.

Characteristics and temporal variation of airborne radon decay progeny in the indoor environment in Catalonia (Spain)

Abstract It is well known that the radioactive dose due to radon progeny indoors depends mainly on the radon exhalation rate and other parameters such as the equilibrium factor (F), unattached fraction (f p ), and particle size distribution. These parameters vary widely from one site to another and with time, according to the characteristics of the site and the climate. This paper summarizes the work carried out in the Spanish region of Catalonia and is a report on the preliminary results of an ongoing study. Four sites were selected according to their characteristics and radon concentration levels. In one of the dwellings, a three-floor house, radon concentration ranging from 10 Bq/m 3 to more than 3500 Bq/m 3 , was found in a set of continuous measurements taken over a period of 90 d. In this house, it was found that the advection form of radon exhalation, through the toilet drain pipe, depended mainly on temperature and wind variations. Parameters, such as F (0.02-0.65) and f p (0-0.70) and particle size distributions, were determined continuously. Average effective dose per unit exposure to radon, during periods of 3 d at least, vary widely between the different dwellings, from 5.4 nSv per Bq m −3 h to 15.6 nSv per Bq m −3 h and may vary in a ratio of more than 8 in the same dwelling.

Activity size distributions for long-lived radon decay products in aerosols collected in Barcelona (Spain)

The activity median aerodynamic diameters (AMADs) of long-lived radon decay product ((210)Pb, (210)Po) in aerosols collected in the Barcelona area (Northeast Spain) during the period from April 2006 to February 2008 are presented. The (210)Po mean AMAD was 420 nm, while the (210)Pb mean AMAD was 500 nm. The temporal evolution of (210)Pb and (210)Po AMADs shows maxima in autumn and winter and minima in spring and summer. (210)Pb AMAD are being used to estimate the mean-residence time of atmospheric aerosols.

Dose conversion factor for radon concentration in indoor environments using a new equation for the F-fP correlation

Since 1994 the radon studies group at the Institut de Tècniques Energètiques (INTE) of the Universitat Politècnica de Catalunya in Barcelona, Spain, has carried out a campaign of continuous measurements of the equilibrium factor (F) and the unattached fraction (f(p)) of radon decay products at four sites which are representative of different environmental characteristics on the Mediterranean littoral of Catalonia, Spain. It has been established that these parameters vary widely, F(0.03-0.87) and f(p) (0-0.72), from one site to another and with time, according to the characteristics of the site and climate. In spite of this variation, the F and f(p) parameters are log-normally or normally distributed. The measurements of F and f(p) show that f(p) is negatively correlated to F by a log-power equation, Ln(1/f(p))=1.90[Ln(1/F)](-0.68), which can be used in all the F range, instead of the commonly used power equation f(p)=aFb suggested by Stranden and Strand and other authors, which fits well for a reduced range of F. Power and log-power equations have been introduced into a simplified dosimetric model in order to estimate the effective dose per unit radon exposure as a function of F. From the log-power equation this value is quite constant and ranged from 9 nSv per Bq m(-3) h to 12 nSv per Bq m(-3) h when F is higher than 0.15. In the case of a lower F factor, a linear function that passes through 0 fits quite well. A value of 12 nSv per Bq m(-3) h is proposed for the Mediterranean littoral of Catalonia as the best estimation.