International Journal of Radiation Research
Volume:3 Issue: 3, Jul 2005

Polymer gels are an emerging new class of dosimeters which are being applied to the challenges of modern radiotherapy modalities. Research on gel dosimetry involves several scientific domains, one of which is the imaging techniques with which dose data is extracted from the dosimeters. In the current work, we present our preliminary results of investigating capability of X-ray CT for extracting brachytherapy dose distributions from a normoxic gel dosimeter. A normoxic radiosensitive polymer gel was fabricated under normal atmospheric conditions and poured into three phantoms. Using Cs137 brachytherapy sources, the phantoms were irradiated with different dose distributions with a LDR Selectron remote after-loader. To improve SNR, 25 images were obtained of each slice for image averaging and an averaged background image of an un-irradiated gel phantom was then subtracted for artifact removal. To further improve the accuracy, a self-consistent normalized method was used for calibration of the dosimeters based on an assumption of a linear dose response between zero and maximum dose regions in the gel. Although results reveal very similar CT-number gradients to that of brachytherapy dose distributions, but the method does not fulfill brachytherapy dosimetry requirements. This might be due to the high prescribed doses in this study which in turn results in a large change in the CT numbers. This change in the CT numbers of the images can not be considered to have a linear relationship with dose which was the basic assumption of our calibration method, so the results are just qualitatively comparable. In this study, the results of using X-ray CT for brachytherapy polymer gel dosimetry is promising but not still satisfying. Improving a proper calibration method for correlating CT numbers to dose will be significantly helpful for performing measurements with CT. The main limitation for CT is still a low signal to noise ratio especially in lower dose areas.

The application of DU emanation for first time contaminated certain areas in the south west region of Iraq after the second Gulf war (1991). These contaminated areas were discovered in 1994. Radioactive contamination was detected using the nuclear enterprise PCM5/1 in soil samples collected from two regions near by grazing lands. This study was done for assessment of DU contaminated soil in the regions under study. Portable detector was used for radiation measurement of the contaminated area. Samples from each region were selected and taken to Baghdad kept in plastic bags for gamma ray spectroscopy measurement. Gamma-ray spectroscopy system consists of high purity germanium (HPGE) detector surrounded by appropriate shield. The measurement of detector efficiency using (GDR) computer programs, supplied by Canberra Company was used to analyze gamma-ray spectrum. The activity of 234 Th, 235 U, 238Pa and other natural isotopes were measured. The measurement by gamma –ray spectrometry system showed that six samples were heavily contaminated with DU, because the presence of 243Pa and 235U peak and the percentage ratio between 235 U/238U were less than 0.005, when both international mathematical methods, namely IAEA and Kosovo, were used. Because of existence of radiation equilibrium between 234Th and 234Pa, the measurements should be accurate. The result showed that six of the samples were heavily contaminated with DU and there is a good agreement between the two methods. Because of the accuracy and ease of the Kosovo method, it is recommended for future investigations.

Monitoring internal exposure of individuals handling significant amounts of iodine-125 (I-125) for iodination is of great importance. These individuals are potentially exposed to external contamination, and internal contamination through inhalation, ingestion and intact skin absorption, to I-125. Considering radiological toxicity of this radionuclide its monitoring in the workplace and workers is necessary for radiation protection purposes. Direct measurement of I-125 in thyroid of individuals, known as a common and reliable method, was applied in the framework of monitoring program. Intakes of I-125 by individuals and the associated effective doses were evaluated using thyroid monitoring results and recommended metabolic models. The monitoring results of the laboratory personnel for a period of 3 years are given and compared. According to the results, the intakes of I-125 by individuals in the early phase of laboratory operations were higher due to insufficient facilities and experience. Improvements in the radiation protection facilities of the laboratory and personnel including provision of personal respiratory protection devices resulted in significant reduction of I-125 intakes. According to 3 years results from the implementation of internal exposure monitoring program for personnel producing I-125 labeled compounds, the exposure levels of the personnel have contineously decreased due to improvements in working conditions and increasing of personnel experiences.

Natural uranium exists in earth crust and seawater. The concentration of uranium might increase by human manipulation or geological changes. The aim of this study was to verify susceptibility of laser flourimetry method to determine the uranium concentration in Caspian Sea and Persian Gulf water. Laser flourimetric method was used to determine the uranium concentration in several samples prepared from Caspian Sea and Persian Gulf water. Biological and chemical substances were eliminated in samples for better evaluation of the method. As the concentration of natural uranium in samples increases, the response of instrument (uranium analyzer) increases accordingly. The standard deviation also increased slightly and gradually. Results indicate that the laser flourimetry method show a reliable and accurate response with uranium concentration up to 100 μg/L in samples after removal of biological and organic substances.

An electron beam generated X-ray spectrum consists of characteristic X-ray and continuous bermsstrahlung. The aim of this research is calculating and comparing X-ray spectra for different target filter of mammograms. Monte Carlo is a very powerful tool to simulate a series of different target-filter assembly in order to calculate the X-ray spectra. MCNP version 4C has been used for simulation set up to calculate X-ray spectra for different target-filter combination of mammograms. The spectra of different and the most commonly used target– filter in mammography equipments (Mo-Mo, Mo-Rh, Rh-Rh, W-Rh, Mo-Al and Rh-Al) have been calculated. The computational results can be used to select a suitable X-ray spectrum for mammography as well as for computing the absorbed dose. Also, the Monte Carlo result of Mo-Mo is in good agreement with the published results.

A computer aided diagnosis system was established using the wavelet transform and neural network to differentiate malignant from benign in a group of patients with histo-pathologically proved breast lesions based on the data derived independ­ently from time-intensity profile. The per­formance of the artificial neural network (ANN) was evaluated using a database with 105 patients'' records each of which consisted of 8 quantitative parameters mostly derived from time-intensity profile using wavelet transform. These findings were encoded as features for a three-layered neural network to predict the outcome of biopsy. The network was trained and tested using the jack­knife method and its performance was then compared to that of the radiologists in terms of sensitiv­ity, specificity and accuracy using receiver operating characteristic curve (ROC) analysis. The network was able to classify correctly the 84 original cases and yielded a comparable diagnostic accuracy (80%), compared to that of the radiologist (85%) by per­forming a constructive association between extracted quantitative data and correspond­ing pathological results (r=0.63, p<0.001). An ANN supported by wavelet transform can be trained to differentiate malignant from benign breast tumors with a reason­able degree of accuracy.

Soft tissue sarcomas of the oral cavity are uncommon malignancies; those of smooth-muscle origin are extremely rare. Leiomyosarcomas of the tongue are very rare. Either surgery or radiation therapy with or without chemotherapy are the treatment modalities which improve prognosis. We are presenting a 32-year-old man with leiomyosarcoma of the lateral aspect of the oral tongue with neck metastasis, who was referred to our radio therapeutic oncology department after glossectomy and radical modified neck dissection. The clinical and pathologic features together with his clinical course will be discussed. Six months after chemoradiotherapy, he developed a single metastasis in his right femur, and then by features of lung metastasis he died in a few weeks, unfortunately.

The presence of primordial radionuclide in human habitats has always been a source of prolonged exposure. Measurement of naturally occurring radionuclides in the environment can be used as baseline to evaluate the impact of non-nuclear activities and also routine releases from nuclear installations. A total of 56 samples from 18 different foodstuff including root vegetables (beetroot, carrot, onion, potato, radish and turnip), leafy vegetables(lettuce, parsley, spinach and white cabbage) and lentil, kidney bean, Soya, eggs, rice, meat, tomato and cooking oil were purchased and analyzed by low level gamma spectrometry. The 226 Ra concentrations from root vegetables varied from 13-62 mBqkg-1 (fw) with turnip of highest concentration, i.e. 62mBq kg-1. Among leafy vegetables; parsley showed the maximum concentration of 228 Ra equal to 173 mBqkg-1 (fw). 226 Ra and 228 Ra contents in the soya, 394 and 578 mBq kg-1 (fw) was much higher than those of other samples respectively. Results indicate that foodstuff consumed by Tehran inhabitants have low radium content and are safe, as far as radium concentrations is concerned.