K. Amgarou

A novel approach for long-term determination of indoor 222Rn progeny equilibrium factor using nuclear track detectors

Abstract A detailed study of the measurement principles of airborne 222 Rn decay products by means of nuclear track detectors (NTDs), taking into account the range of variation of the parameters influencing their concentration indoors, has shown that it is not possible for the existing methods to obtain the associated long-term equilibrium factor with an appropriate accuracy. For this reason, we have established a novel approach based on the new concept of reduced equilibrium factor, which can be obtained from the only measurement of airborne 222 Rn and its α-emitter daughter ( 218 Po and 214 Po) concentrations using a passive, integrating and multi-component system of NTDs. We have found that the equilibrium factor has a linear dependence on the reduced equilibrium factor regardless the values taken for the rates of ventilation, of aerosol attachment and of surface deposition. By using well-controlled exposures in a reference laboratory, we have shown that the equilibrium factor values determined with our system agree with those obtained by active monitors. Finally, as a pilot test, several dosimeters were exposed in an inhabited Swedish single-family house. The results of this exposure suggest the usefulness of this method to perform routine surveys in private homes and in workplaces in order to estimate the annual effective dose received by the general public and the workers due to the presence of 222 Rn daughters.

Estimation of neutron-equivalent dose in organs of patients undergoing radiotherapy by the use of a novel online digital detector

Neutron peripheral contamination in patients undergoing high-energy photon radiotherapy is considered as a risk factor for secondary cancer induction. Organ-specific neutron-equivalent dose estimation is therefore essential for a reasonable assessment of these associated risks. This work aimed to develop a method to estimate neutron-equivalent doses in multiple organs of radiotherapy patients. The method involved the convolution, at 16 reference points in an anthropomorphic phantom, of the normalized Monte Carlo neutron fluence energy spectra with the kerma and energy-dependent radiation weighting factor. This was then scaled with the total neutron fluence measured with passive detectors, at the same reference points, in order to obtain the equivalent doses in organs. The latter were correlated with the readings of a neutron digital detector located inside the treatment room during phantom irradiation. This digital detector, designed and developed by our group, integrates the thermal neutron fluence. The correlation model, applied to the digital detector readings during patient irradiation, enables the online estimation of neutron-equivalent doses in organs. The model takes into account the specific irradiation site, the field parameters (energy, field size, angle incidence, etc) and the installation (linac and bunker geometry). This method, which is suitable for routine clinical use, will help to systematically generate the dosimetric data essential for the improvement of current risk-estimation models.

Simultaneous measurement of radon, radon progeny and thoron concentrations using Makrofol-DE detectors

Abstract In this study we describe the set-up of a new passive integrating system to measure simultaneously 222Rn, 222Rn progeny (218Po and 214Po) and 220Rn concentration indoors. It consists of four Makrofol-DE (polycarbonate) circular foils. Two are enclosed within two diffusion chambers—each one with a different filter membrane—to measure 222Rn and 222Rn+220Rn. The other two foils are kept in direct contact with air and are electrochemically etched at different conditions to obtain the 222Rn daughters. Theoretical sensitivities of each Makrofol-DE foil are calculated using Monte-Carlo technique. The calculations are performed taking into account: (1) the Bethe–Blochs expression for the stopping power of heavy charged particles in a medium, (2) the properties and behaviour of 222Rn, 220Rn and their progeny in the open air and within the diffusion chamber and (3) the etching conditions used to visualise α-particles tracks.

On line neutron dose evaluation in patients under radiotherapy

Current improvements in radiotherapy require methods to evaluate their costs and benefits. A possible counterpart of the benefit is the creation of a secondary, radiation induced cancer. A new procedure is presented to assess the peripheral dose delivered to the patients due to photo-neutrons by means of a new on line digital detector. The events in the monitor have been correlated with the neutron dose by Monte Carlo simulations and experimental measurements using CR39 and TLD. This digital detector was employed at 6 different linacs, with energies ranging from 6 to 23 MV, obtaining the doses received in each organ of the patient. Additionally, the ambient dose equivalent was determined finding values from 0 to 470 mSv for complete treatments.

Semi-automatic evaluation system for nuclear track detectors applied to radon measurements

Abstract A global semi-automatic evaluation system has been set up in our laboratory to scan and count etched tracks in both Makrofol-DE and LR-115 detectors. This methodology is, in principle, fully adaptable to any chemical and electrochemical etched track detector. The main advantage it offers is a considerable reduction of the counting time in comparison with the traditional methods using optical devices — microscope or microfiche reader depending on the track size — and a wide detectable range. In addition, it yields accurate, reliable and quite reproducible results. It has been used to measure the track density in both Makrofol-DE and LR-115 based radon and radon daughter detectors. A detailed description of this method is presented in this paper. Results from a comparison study between this system and ocular counting and from experimental calibration are presented as well. The correspondence between the results of the semi-automatic system and those obtained directly with ocular counting has been found to be rather good.

Measurement of the 214Po concentration in air using Makrofol-DE detectors

Abstract The measurement of the 214 Po concentration in air with Makrofol-DE detectors is useful to estimate the long-term averaged equilibrium factors indoors. To differentiate α-particles emitted by 214 Po from those emitted by 218 Po and 222 Rn, the detector must register only α-particles with energies between 6.2 and 7.5 MeV. The required energy response is obtained only if a removed layer of about 43 μm is achieved in a chemical etching of the detector. The methodology used to determine the etching conditions is described in this paper. The optimum conditions found are: a) chemical etching for 6 h at a temperature of 40°C, using 7.5 M KOH mixed with 50% ethanol as an etchant, and b) electrochemical etching for 1 h at a frequency of 3 kHz and an electric field strength of ∼ 34 kV cm −1 . Several dosimeters have exposed during 2 months in dwellings located in the Barcelona area, Spain. A 214 Po averaged concentration of (13.6 ± 8.6) Bq m −3 was obtained.

Neutron spectra inside an adult and children anthropomorphic phantoms in high energy radiotherapy

This work presents the results of the Monte Carlo simulation of the neutron fluence energy spectra at 16 representative points inside three anthropomorphic phantoms mimicking an adult and two children. Simulations were carried out using the MCNPX-2.6.0 code, and the calculation of the neutron spectra for each beam incidence was made in a single simulation file, including the treatment room, each phantom and the linac. Results show that pediatric patients are exposed to higher neutron fluence than adults. Consequences in terms of an increased secondary cancer risk should be analysed.

Neutron spectrometry and determination of neutron ambient doses in radiotherapy treatments under different exposure conditions

A project has been set up to study the effect on a radiotherapy patient of the neutrons produced around the LINAC accelerator head by photonuclear reactions induced by the gamma radiation above ~8 MeV. These neutrons may reach directly the patient, or they may interact with the surrounding materials until they become thermalised, scattering all over the treatment room and affecting the patient as well, contributing to the peripherical dose. Spectrometry was performed with a set of Bonner spheres at 50 cm from the isocenter and at the place where a digital device for measuring neutrons will be located the treatment room. Exposures have taken place in six linac accelerators with different energies (from 6 to 23 MV). A summary of the spectrometry results and of the neutron doses received by the patient is presented.

Neutron Contamination in Medical Linear Accelerators Operating at Electron Mode

Nowadays, neutron contamination in high energy photon beams normally used in radiotherapy treatments is an issue of interest from the radioprotection point of view. However, neutron production when using electron beams to treat superficial tumors has usually been ignored. The aim of this paper was to study such contamination and its effect on patients. In order to do that, experimental measurements in a radiotherapy environment were carried out using a digital device sensitive to thermal neutrons. Besides, Monte Carlo simulations were performed to estimate the difference in number of particles between photon and electron operational modes, required to deposit the same dose at a certain depth. Results show that neutron production is lower for electron beams than photon ones but not as low as previously expected.

Neutron Distribution in Radiotherapy Treatment Rooms

Neutrons have a high biological effectiveness. Therefore, patient exposition to them represents a relevant issue and consequences to this exposure, regarding secondary cancer induction, must be clarified. The aim of this work was to make a complete study on the production of photoneutrons in radiotherapy facilities. Detailed Monte Carlo simulation, using MCNPX code, was performed to characterize the neutron generation in a Siemens PRIMUS linac operating at 15 MV and to determine the fluence energy distributions inside the treatment room. This information is mandatory to understand the response, under radiotherapy conditions, of a new neutron digital detector developed by our group.