International Journal of Radiation Research
Volume:1 Issue: 4, Oct 2003

Radon, an invisible, odorless, heaviest (nine times heavier than air) and radioactive gas is an aberration (the only gas in the long decay chain of heavy metal elements). It is ubiquitously present in dwellings and in the environment. Humans receive the greatest radiation dose in their homes. That''s where they spend most time - typically 70%, more for small children. Recent worldwide surveys reveal that an average person receives each year more radiation from radon than from all other natural or man-made sources combined. Over the years, the radiation exposure accumulated at home may exceed the exposure of uranium miners and lead to lung disorders. Therefore it is fundamental and justified to make a quantitative assessment of the radon in dwellings and the environment of work place. In this study, measurement of radon and its progeny levels was carried out in the environment of an oil refinery. Besides, radon and its progeny levels were also measured in the dwellings situated on the refinery premises and the dwellings in the city for comparison. LR-115, Type- II (Kodak Pathe, France), plastic track detectors commonly known as solid state nuclear track detectors (SSNTDs) were used to measure the radon concentration over long integrated times. Alpha particles emitted from radon cause radiation damage tracks, which were subsequently revealed by chemical etching in NaOH. These alpha tracks registered were counted by optical microscope at suitable magnification and converted into radon concentration. The geometric means (GM) of potential alpha energy concentration (PAEC), Equilibrium Equivalent Concentration of radon (EEC value), annual exposure and annual effective dose in the environment of refinery premises was 10.09 mWL, 93.43 Bq m-3, 0.41 WLM and 1.61 mSv, in refinery dwellings 12.21 mWL, 112.96 Bq m-3, 0.50 WLM and 1.94 mSv and in city dwellings 8.24 mWL, 76.23 Bq m-3, 0.34 WLM and 1.31 mSv respectively. The dose levels in the refinery premises were found to be marginally below the ICRP recommendations. The radon and its progeny levels were higher in the dwellings of refinery township as compared to the city dwellings. While studying seasonal variation, it was found that the measured values of radon and its progeny levels were higher in winter (November to February) than in summer (May to August). This study showed that the presence of fossil fuels like natural gas, LPG etc. in the environment had resulted into higher levels of radon and its progeny in the refinery dwellings.

CT is a diagnostic imaging modality giving higher patient dose in comparison with other radiological procedures, so the calculation of organ dose in CT exams is very important. While methods to calculate the effective dose have been established (ICRP 26 and ICRP 60), they depend heavily on the ability to estimate the dose to radiosensitive organs from the CT procedure. However, determining the radiation dose to these organs is problematic, direct measurement is not possible and comparing the dose as functions of scan protocol such as mA is very difficult. One of the most powerful tools for measuring the organ dose is Monte Carlo simulation. Today the predominant method for assessment of organ absorbed dose is the application of conversion coefficients established by the use of Monte Carlo simulations. One of the most famous dose calculation software is CTDOSE, which we have used it for calculation of organ dose. In this work we measured the relationship between the mA, KV and scanner type with the equivalent organ dose and effective dose in mathematically standard phantom (Hermaphrodite 170cm/70Kg) in an abdomen-pelvis CT exam by Monte Carlo method. For this measurement we increased the mA in steps of 10 mA and plot curves for organ dose as a function of mA for different KV setting. As expected, with increasing mA, patient organ dose increased, but the simulation results showed that the slope of organ dose as a function of mA increased with KV increasing. By increasing KV from 120 to 140 the increase in slope of curves representing patient organ dose versus mA for different scanner types show almost similar behavior whereas the slope of the corresponding curves in scanners which equipped xenon detectors was almost 22% more than the slope of scanners equipped with scintillation detectors. Our research showed that regarding equivalent dose the system incorporating scintillation detector has a superior performance. Incorporating such software in various CT scanners, marketed by different vendors, will offer the ability to get a print out of patient organ dose in any examination according to the imaging parameters used for imaging any part of the body

Most of our current understanding of the biological effects of exposure to ionising radiation is based on conventional cytogenetic techniques, which enable us to determine the relationship between chromosomal aberration and dose received by radiation workers. However, conventional techniques have numerous limitations and chromosomal aberrations can be easily missed. Since FISH plays an important role in detecting chromosomal changes, this method was used to reassess data derived from previous studies employing conventional techniques. Two groups of radiographers were the subject of a study on conventional chromosomal aberration and fluorescence in situ hybridisation (FISH) for translocation. The first group was chosen following an accidental contamination incident in a nuclear medicine department. The second group was composed of six radiographers working in an X-ray department with a previous record of overdose as recorded by film-badges; these workers had been the subjects of a previous chromosomal study. Coded blood samples from 11 radiographers and 11 controls were analysed for chromosomal aberration and by FISH for translocation. 200 metaphases from the peripheral blood lymphocytes per subject were analysed to investigate possible frequencies of chromosome and chromatid type aberration and 2000 metaphases per subject were scored in FISH method. There was no significant difference between the radiographers and the control groups in conventional analysis; also there was no significant difference at the 95% level of confidence in FISH analysis. There was no correlation between levels of translocation and total lifetime doses from occupational (according film-badge and TLD) and/or background irradiation. The overall conclusion is that the frequency of chromosomal damage in both groups of radiographers did not exceed that of the control group.

Medical x-rays are the largest man-made source of public exposure to ionizing radiation. It is important to avoid conditions where the amount of radiation used is more than that needed for the procedure. The Entrance Skin Exposure (ESE) measurement was conducted for quality control of x-ray machines and survey of operator’s experimental techniques. The ESEs were measured by UNFORS dosimeter for five common types (12 projections) of x-ray procedures in standard man for the 18 public hospitals of Yazd province. The median, 3rd quartile, minimum, and maximum values of each ESEs distributions are reported. The 12 histograms are presented showing wide distribution of measured ESE in each examination. The survey results are compared with guide levels that reported by CRCPD or NRPB. The sum of ESEs measurements such as in skull, Th-spine and L-spine are projection out of the guide levels. One of reasons of the wide ESEs distribution is miss unique role in selection of techniques for the same procedure and same patient size by operators in each center and even for one x-ray machine. The findings support the importance of the on-going quality assurance program to ensure doses are kept to a level consistence with optimum imaging quality.

In myocardial perfusion SPECT imaging, images are degraded by photon attenuation, the distance-dependent collimator, detector response and photons scatter. Filters greatly affect quality of nuclear medicine images A phantom simulating heart left ventricle was built. About 1mCi of 99mTc was injected into the phantom. Images were taken from this phantom. Some filters including Parzen, Hamming, Hanning, Butterworth and Gaussian were exerted on the phantom images. By defining some criteria such as contrast, signal to noise ratio, and defect size detectability, the best filter can be determined. 0.325 Nyquist frequency and 0.5 Nq was obtained as the optimum cut off frequencies respectively for hamming and hanning filters. Order 11, cut off 0.45 Nq and order 20 cut off 0.5 Nq obtained optimum respectively for Butterworth and Gaussian filters. The optimum member of every filter’s family was obtained.

Within the context of developing techniques to facilitate the diagnosis of the thyroid diseases, the elemental composition of pathological thyroid tissue (neoplastic and non-neoplastic) was investigated by proton induced X-ray emission. The PIXE has been widely used as a sensitive technique for trace elemental analysis in both biological and medical fields. The twenty-eight specimen of thyroid tissue (neoplastic, non-neoplastic and grossly normal tissue) were obtained from operation of 14 patients with different thyroid diseases. Determination of the heavy trace elements distribution (Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Mo, I) was carried out by irradiating of the sample surface with a focused proton beam. Fourteen grossly normal, eleven non-neoplastic and three malignant thyroid neoplasm cases were diagnosed. Trace element contents of the International Atomic Energy Agency (IAEA) MA-B-3/TM Fish tissue was used as standard for calibration of PIXE set up. The concentration of the heavy trace elements Co, Cu, Zn and Mo in neoplasm of thyroid were higher than other samples. The concentration of the heavy trace elements, Fe, As, Br, Rb, I, are found to be much lower in neoplasm of thyroid than non–malignant and grossly normal thyroid tissue. The concentration of the Se, Co and I in this study is consistent with the others study but there are differences in the concentration of Fe in our study and others works. Iodine concentrations was 11 times lower, on average in neoplasm compared with non-neoplasmic tissue of thyroid. The low levels of I in thyroid neoplasm are correlated to some pathological factors.

We designed an algorithmic model based on the logistic regression analysis and a non-algorithmic model based on the Artificial Neural Network (ANN). The ability of these models was compared together in clinical application to differentiate malignant from benign breast tumors in a study group of 161 patients'' records. Each patient’s record consisted of 6 subjective features extracted from MRI appearance. These findings were encoded as features for an ANN as well as a logistic regression model (LRM) to predict biopsy outcome. After both models had been trained perfectly on samples (n=100), the validation samples (n=61) were presented to the trained network as well as the established LRMs. Finally, the diagnostic performance of models were compared to that of the radiologist in terms of sensitiv­ity, specificity and accuracy, using receiver operating characteristic curve (ROC) analysis. The average output of the ANN yielded a perfect sensitivity (98%) and high accuracy (90%) similar to that one of an expert radiologist (96% and 92%) while specificity was smaller than that (67% verses 80%). The output of the LRM using significant features showed improvement in specificity from 60% for the LRM using all features to 93% for the reduced logistic regression model, keeping the accuracy around 90% Results show that ANN and LRM prove the relationship between extracted morphological features and biopsy results. Using statistically significant variables reduced LRM outperformed of ANN with remarkable specificity while keeping high sensitivity is achieved.

Leiomyosarcoma is a rare entity in prostate but it is the most common type of prostate sarcomas in adult patients. In most reported series the prognosis is poor and the median survival is about 15-18 months. Hereby we present a 72 years old man who received combined modality treatment including radical surgery followed by adjuvant chemotherapy and radiotherapy. He has been well for 14 months, but now he is suffering from lung metastases and asymptomatic local recurrence. I