Volumen 25 (2019): Edición 4 (December 2019)

The nuclear reaction ¹⁹F(p, αγ)¹⁶O is presented as a valid method to measure the fluorine content in the first superficial layers of teeth. The analysis is performed in-vitro in extracted teeth, both healthy, fluorotic and decayed. It is performed irradiating the tooth with an energetic proton beam and analyzing the emitted high energy alpha particles. The quantitative analysis is performed comparing results with that of a standard sample at a known concentration. The depth profile of fluorine has a maximum content in the first superficial layers. The average concentrations in healthy enamel are of the order of 2 mg/g; it is of about 10 mg/g in fluorotic teeth, and below 0.1 mg/g in decayed teeth. The concentration in the dentine is about 50% lower than in the enamel and the concentrations decrease going from incisors to premolar and to molar teeth. Many results and a literature comparison are presented and discussed.

The main objective of our work is to measure ²³⁸U, ²³²Th, ²²²Rn and ²²⁰Rn in different table oil samples using a method based on the use of two types of solid nuclear track detectors: CR- 39 and LR-115 II in order to determine the doses of radiation received by the individuals following ingestion of the samples of table oil studied. Indeed, we have developed an original method based on the determination of the detection efficiencies of CR-39 and LR-115 II solid nuclear track detectors for alpha particles emitted from the uranium 238 and thorium 232 series to evaluate ²³⁸U, ²³²Th, ²²²Rn and ²²⁰Rn concentrations in different table oil samples. We were able to determine doses of radiation due to ²³⁸U, ²³²Th and ²²²Rn received by individuals of the Moroccan, French, Italy, Spain and Tunisia populations following the ingestion of table oil.

The effective doses committed due to ²³⁸U, ²³²Th, and ²²²Rn following the ingestion of the table oil by the consumers were determined. The maximum total committed effective dose was found equal to (10±0.7) µSv·y⁻¹ of the Moroccan population, (11.6±0.7) µSv·y⁻¹ of the French population, (10.3±0.7) µSv.y⁻¹ of the Italian population, (10.4±0.5) µSv·y⁻¹ of the Spanish population and (10.5±0.7) µSv·y⁻¹ of the Tunisian population is much lower than the average dose given by the United Nations Scientific Committee on the Effects of Atomic Radiation [1] for ingestion (0.2 to 0.8 mSv·y⁻¹). The results obtained using our method are in very good agreement with those obtained using the model of the International Commission on Radiological Protection

The aim of the current research was to study the radiation shielding properties of polyurethane-based shielding materials filled with B₄C, BeO, WO₃, ZnO, and Gd₂O₃ particles against fast neutrons. The macroscopic cross sections of composites containing micro- and nanoparticles with a diameter of 10 µm and 50 nm were calculated using MCNPX (2.6.0) Monte Carlo code. The results showed that adding nano-scaled fillers to polyurethane matrix increases attenuation properties of neutron shields compared to micro-scaled fillers for intermediate and fast neutrons. Among the studied composites, WO₃ and Gd₂O₃ nano-composites presented higher neutron cross section compared to others.

Biomedical accelerators used in radiotherapy are equipped with detector arrays which are commonly used to obtain the image of patient position during the treatment session. These devices use both kilovolt and megavolt x-ray beams. The advantage of EPID (Electronic Portal Imaging Device) megavolt panels is the correlation of the measured signal with the calibrated dose. The EPID gives a possibility to verify delivered dose. The aim of the study is to answer the question whether EPID can be useful as a tool for interfraction QC (quality control) of dose and geometry repeatability.

The EPID system has been calibrated according to the manufacturer’s recommendations to obtain a signal and dose values correlation. Initially, the uncertainty of the EPID matrix measurement was estimated. According to that, the detecting sensitivity of two parameters was checked: discrepancies between the planned and measured dose and field geometry variance. Moreover, the linearity of measured signal-dose function was evaluated.

In the second part of the work, an analysis of several dose distributions was performed. In this study, the analysis of clinical cases was limited to stereotactic dynamic radiotherapy. Fluence maps were obtained as a result of the dose distribution measurements with the EPID during treatment sessions. The compatibility of fluence maps was analyzed using the gamma index. The fluence map acquired during the first fraction was the reference one. The obtained results show that EPID system can be used for interfraction control of dose and geometry repeatability.

An estimate of patient dose, patient size should be used to normalise the output dose of CT machine in the terms of volume CT dose index, CTDI_vol. There are two metrics to characterise the patient size, i.e. the effective diameter (D_eff) and the water-equivalent diameter (D_w). These two metrics could be estimated by patient age. However, to date, relationships between the age and head patient size (D_eff and D_w) have not been established for the pediatric patients. The aim of this study was to establish the relationships between the age and head patient size (D_eff and the D_w) as the basis for calculating the size-specific dose estimate (SSDE) for paediatric head CT examination. The data were retrospectively collected from serial images of the CT head in the DICOM file from one hundred and thirteen paediatric patients aged 0-17 years (63 male and 50 female patients) underwent head CT examinations. The patient’s sizes (D_eff and D_w) were calculated from the patient’s images using the IndoseCT version 15a software. The D_eff and D_w values were correlated with age of patients using regression analysis. It was found that patient size (D_eff and D_w) correlated well with the age of the patient with R² more than 0.8. The size of the D_w is bigger than the D_eff. The D_eff values for male patients are 12.38 to 16.21 cm, and D_w values are 11.96 to 18.16 cm, respectively. For female patients, the values of D_eff are from 11.54 to 16.87 cm, and the values of D_w are from 11.60 to 17.86 cm, respectively.

Irreversible electroporation (IRE) is a process in which the cell membrane is damaged and leads to cell death. IRE has been used as a minimally invasive ablation tool. This process is affected by some factors. The most important factor is the electric field distribution inside the tissue. The electric field distribution depends on the electric pulse parameters and tissue properties, such as the electrical conductivity of tissue. The present study focuses on evaluating the tissue conductivity change due to high-frequency and low-voltage (HFLV) as well as low-frequency and high-voltage (LFHV) pulses during irreversible electroporation. We were used finite element analysis software, COMSOL Multiphysics 5.0, to calculate the conductivity change of the liver tissue. The HFLV pulses in this study involved 4000 bipolar and monopolar pulses with a frequency of 5 kHz, pulse width of 100 µs, and electric field intensity from 100 to 300 V/cm. On the other hand, the LFHV pulses, which we were used, included 8 bipolar and monopolar pulses with a frequency of 1 Hz, the pulse width of 2 ms and electric field intensity of 2500 V/cm. The results demonstrate that the conductivity change for LFHV pulses due to the greater electric field intensity was higher than for HFLV pulses. The most significant conclusion is the HFLV pulses can change tissue conductivity only in the vicinity of the tip of electrodes. While LFHV pulses change the electrical conductivity significantly in the tissue of between electrodes.