Showing papers in "Iranian Journal of Medical Physics in 2008"

Determination of dosimetric parameters of the second model of pd-103 seed manufactured at agricultural, medical and industrial research school

Abstract: Introduction: The use of low energy isotopes such as 103 Pd in brachytherapy for the treatment of cancers such as prostate, eye, head, neck, breast and cervix is increasing. In this regard, different models of Pd- 103 seeds have been designed and manufactured at the Agricultural, Medical and Industrial Research School (AMIRS) of Atomic Energy Organization of Iran. In this research, the dosimetric parameters of the second model of Pd-103 seed manufactured at AMIRS have been calculated and measured. Materials and Methods: The dosimetric parameters of the second Pd-103 seed manufactured at AMIRS were determined according to TG-43U1 protocol using Monte Carlo calculations (MCNP4C computer code) and measurements performed using TLD-GR200A dosimeters in a Perspex phantom. The parameters include dose rate constant, geometry function, radial dose function, anisotropy function, anisotropy factor and anisotropy constant. Results: It was found that by using MCNP4C code the calculated dose rate constant in water and Perspex was 0.706±0.001 and 0.501±0.001 cGyh -1 U -1 , respectively. Using the calculated geometry function, the radial dose function and the anisotropy function were determined by experimental and theoretical methods in water and Perspex phantom. Also, the calculated value of anisotropy constant in water was equal to 0.88. Discussion and Conclusion: A discrepancy of less than 10% between the calculated and the measured values indicates a reasonable agreement between the simulation and the measurement method. Also, the dosimetric parameters of this seed have been compared to the dosimetric parameters of the first Pd-103 seed manufactured at AMIRS and some other seeds. The obtained results indicate that the seeds manufactured at AMIRS have acceptable dosimetric parameters suitable for brachytherapy applications.

Gamma dose rate measurement and dose rate calculation for sensitive organs in the vicinity of hot springs in kerman province

Abstract: Introduction: All of the people worldwide are exposed to low levels of radiation. Cancer induction and genetic disorders are among the hazards of low level exposure. In some cases, radiation close to hot springs is higher than normal areas due to a high concentration and the decay products of Ra-226. Given the use of hot springs by the general public because of their therapeutic properties, preparation of a guideline based on radiation levels of hot springs is believed to be necessary. In this study, gamma dose rate in the vicinity of hot springs in Kerman province was measured and the dose rates for sensitive organs were calculated. Materials and Methods: The equipments used in this study were an RDS-110 survey meter, a tripod with an aluminum frame, a chronometer and a thermometer. After defining 19 stations (one near each hot spring), the survey meter was fixed horizontally one meter above the hot spring and the gamma dose rate was recorded during one hour. Then, using the corresponding coefficients, equivalent, effective, bone marrow and reproductive organs dose rates were calculated. Independent T test and variance analysis were used for comparison of the means. Results: Gamma absorbed dose rates near nineteen hot springs in Kerman province were measured. The results showed that Amirekeykhosravi Spring had the highest annual dose rate (1.65 ± 0.54 1 mSvy ) and Gharayoob Spring had the lowest annual dose rate (0.53 ± 0.23 1 mSvy ). Also, the annual bone marrow and reproductive organs dose rates were within the ranges 0.42 ± 0.18 1 mSvy to 1.32 ± 0.43 1 mSvy and 0.43 ± 0.19 1 mSvy to 1.34 ± 0.44 1 mSvy , respectively. Discussion and Conclusion: This study shows that the maximum annual dose rate in the vicinity of the hot springs in Kerman province was 120% higher than the outdoors annual dose rate for normal areas. This is due to the existence of radioactive elements in spring water and the high altitude of the springs from the sea level. Due to the high dose rate to sensitive organs, it is suggested that Chegeri, Ghaneghah, Gharayoob, Joshan and Chaharfarsakh springs are used as spas. Also, according to the results, there is no correlation between the gamma dose rate and the temperature of the springs.

Effect of Cell Size and Shape on Electric Field Threshold and Critical Transmembrane Voltage for Electroporation

Abstract: Introduction: Electroporation is a technique for increasing the permeability of the cell membrane to otherwise non-permeate molecules due to an external electric field. This permeability enhancement is detectable if the induced transmembrane voltage becomes greater than a critical value which depends on the pulse strength threshold. In this study, the variability of the electric field threshold and the minimal transmembrane voltage resulting in detectable electroporation of the plasma membrane of spherical and irregularly shaped cells have been investigated. Materials and Methods: Spherical cells of different dimensions and attached cells of various shapes were selected. The chosen cells were exposed to 100 0s electric pulses with incrementing amplitudes. Electroporation was detected by an increase in the fluorescence caused by an influx of Ca 2+ and the threshold electric field for each cell was recorded. A 3D geometrical model of each cell was constructed from its cross sectional images. Simulation using the finite element method was performed to obtain the critical induced transmembrane voltage for each individual cell. Results: The magnitudes of the electric field strength threshold and critical transmembrane voltage versus cell radius were obtained for spherical cells. To investigate the effects of cell shapes and orientations on the field strength threshold and critical voltage, the considered attached cells were categorized into three different groups. Field strength threshold and critical voltage was obtained for each cells and the results for the different groups were compared. Discussion and Conclusion: Size, shape and orientation of cells affect the critical transmembrane voltage and all these elements in turn influence the electric field threshold and, therefore, the efficiency of electroporation.

Treatment of Colon Carcinoma Tumors by Electrolysis: Effect of Electrical Dose and Polarity

Abstract: Introduction: As a physical treatment, electrochemical therapy (ECHT) has provided an effective and useful approach for treating localized tumors. The chemical changes due to a direct electric current destroy the tumor. This study evaluates the effect of electrical dose and polarity on the efficacy of the treatment of a colon tumor model. Materials and Methods: In order to induce tumors, 5 × 10 5 CT26 cells were injected into the right dorsal side of 100 Balb/c mice subcutaneously. When the mean volume of the tumors reached 350 ± 50 mm 3 , they were randomly divided into 2 control and 8 test groups, each consisting of 10 mice. Six platinum electrodes (3 cathodes and 3 anodes) were inserted into the base and the apex of each tumor. Electrical doses of 0, 10, 20, 30 or 40 C/cm 3 were then applied. Tumors volumes were subsequently measured daily and the mortalities were recorded. A histopatholological study was also performed. Results: After ECHT, a decrease in tumor volume and also an increase in necrosis and cumulative survival were statistically significant. In the control groups, the tumors were not destroyed and the mice did not survive more than 50 days. With 40 C/cm 3 electrical dosage and anode electrode polarity applied to bases of the tumors, 80% of the tumors showed complete response until 120 days post-treatment. Increasing the electrical dose caused a statistically significant effect on the complete response percentage and the cumulative survival fraction. Applying anode polarity to the bases of the tumors produced better results although without statistical significance. Discussions and Conclusions: Complete response in the treatment groups (10 to 80 percent) demonstrates the antitumor effects and the high potential of electrolysis for tumors eradication. Also, occurrence of only one death event in the highest electrical dose group and the good health of the animals until 120 days after treatment demonstrate that electrolysis is a safe technique.

The Measurement of Low Frequency Magnetic Field of Two Kinds of GSM900 Mobile Phone

Abstract: Introduction: The use of mobile communication systems has dramatically increased over the past decade. Although many studies have been performed to determine the effect of radio frequency (RF) but less attention has been paid to the possible biological impact of exposure to extremely low frequency (ELF) components. The objective of this study is two folds. One is to design the equipments needed for the measurement of the ELF fields of two types of GSM900 mobile phone. Secondly, use a protocol suitable for an accurate assessment of the ELF fields. Materials and Methods: First a home-made search coil was provided and calibrated precisely under several experiments. Using Fast Fourier Transform, the power spectrum density of the induced voltage in the search coil was analyzed and the amplitudes of 217 Hz and its harmonics were extracted and then the distribution of magnetic field in the back side of mobile phones was determined. Results: The values of B-field on the back side of the two kinds of GSM mobile phone were different. They were between 50 to 160 µT in Nokia 3310 and 14 to 30 µT in Nokia 8310. Considering the difference between the amplitudes of frequency components at 217 Hz and its harmonics in the two kinds of mobile phone, a range of magnetic flux density at different times in a five day period was measured. Discussion and Conclusion: These findings emphasize the need for considering the distribution of low frequency magnetic field from mobile phone when biological effects of magnetic fields are studied. To determine the intensity windowing effect, one must consider the physical characteristics of the fundamental frequency component wave (217 Hz) and its harmonics produced by the mobile phone similar to the one generated under a real situation.

A hybrid method for mammography mass detection based on wavelet transform

Abstract: Introduction: Breast cancer is a leading cause of death among females throughout the world. Currently, radiologists are able to detect only 75% of breast cancer cases. Making use of computer-aided design (CAD) can play an important role in helping radiologists perform more accurate diagnoses. Material and Methods: Using our hybrid method, the background and the pectoral muscle were removed from mammography images and image contrast was enhanced using an adaptive density weighted method. First, suspected regions were extracted based on mathematical morphology and adaptive thresholding approaches. Then, in order to reduce the false positives in the suspected regions obtained in the first stage, the corresponding features were extracted using a wavelet transform, followed by the application of a support vector machine to detect masses. Results: A Mammographic Image Analysis Society (MIAS) database was used to evaluate the performance of the algorithm. The sensitivity of 81% and specificity of 84% were achieved in detecting masses. Improvement of sensitivity and specificity with our proposed hybrid algorithm was demonstrated by subjective expert-based and objective ROC-based techniques in comparison with the currently acceptable method by Masotti. Disscusion and Conclusion: In this paper, a hybrid method of pixel-based and region-based mass detection approaches is proposed to increase the specificity of the results. The accessory stage (using wavelet features) increased the sensitivity by 30%. It can be concluded that the proposed algorithm is an efficient and robust method for different types of mass detection in low-quality mammography images.

Monte Carlo Dose Calculation of 90 Sr/ 90 Y Source in Water Phantom

Abstract: Introduction: 90 Sr/ 90 Y source has been used for the intravascular brachytherapy to prevent coronary restenosis in the patients who have undergone angioplasty. The aim of this research is to determine the dose distribution of 90 Sr/ 90 Y source in a water phantom. Materials and Methods: In the present work, MCNP code has been applied to calculate the dose distribution around a 3 cm length of 90 Sr/ 90 Y source in a 30×30×30 cm 3 water phantom. Also, the exact geometry of the source has been used in this simulation. Tally *F8:e which is suitable for beta ray dosimetry has been evaluated with less than %5 relative error in a sphere having 0.2 mm radius. Results: The isodose curve for 10, 20, 40, and 90% depth dose (PDD) were derived based on the calculated dose curves along the parallel and perpendicular axis to the source. Discussion and Conclusion: The results obtained in this work are in a good agreement with the experimental result published by Buckley et al. and the International Atomic Energy Agency (IAEA) report in a water phantom. Therefore, the result of this research can be used in the intravascular brachytherapy.

Studying the mechanical behavior of tissue in the generation of pressure sores using simulation and a guinea pig experimental model

Abstract: Introduction: Pressure sores refer to lesions that are produced while a constant pressure causes necrotic tissue to grow. The need for a better comprehension of the process has led researchers to artificial generation of pressure sores. Modeling the mechanical behavior of tissue will provide a better understanding of this process as well as a more suitable selection of system parameters. Materials and Methods: In this research, the mechanical behavior of tissue was modeled using the finite element method. A system with pressure sensors and a suitable feedback mechanism was used to generate pressure sores. The elastic parameters of tissue were obtained using uniaxial tensile strength tests. The thicknesses of skin layers were calculated by taking microscopic images of skin samples and using Motic Images 2000 version 1.2 software. Results: The results of the finite element modeling illustrate the strain and stress profiles in tissue layers. The maximum values of deviatory strain occurred under the border of the disc in the muscle layer. Deviatory and shear stresses reached their maximum values under the center of the disc in the skin layers. Discussion and Conclusion: The simulation and experimental results are in good agreement. Therefore, the introduced model may be used for better comprehension of tissue behavior. Better results may be obtained by finding a more accurate method for calculating tissue parameters.