Showing papers in "Iranian Journal of Medical Physics in 2011"

Excess Cancer Risk Assessment from Some Common X-Ray Examinations in Sabzevar County

Abstract: Introduction: Nowadays ionizing radiation has a considerable contribution in medical diagnostic and treatment. Using ionizing radiation is increasing rapidly, so biological effects of ionizing radiation should be considered more. X-rays in the range of diagnostic radiology have hazardous effects and risks that are defined as random effects. These effects obey the LNT hypothesis that occur at low doses and include many types of cancer and genetic mutations. So it is very important to assess the risk of exposure in medical examinations. Cancer is one of these hazardous risks caused by low dose ionizing radiation that may occur during life after exposure. According to BEAR 7, low dose radiation is defined as radiation that produces doses near zero up to 100 mSv. Materials and Methods: This work was carried out in eight radiology centers in the Sabzevar county of Iran for 485 patients in eight typical x-ray examinations chosen for the study: chest PA, chest AP, lumbar spine AP, lumbar spine LAT, pelvis AP, abdomen AP, skull AP and Lat. In order to estimate the excess cancer risk, we need to obtain collective effective dose caused by radiation in the study population. Usually effective dose offers precise assessment of radiography examination injuries in adult patients. In this study, we used the PCXMC Monte Carlo based software to obtain effective dose and organ dose. This software calculates organ and effective dose following input of patient and radiographic conditions. Results: Average patient weight and height, entrance surface dose, parameters used for each type of examination, and DAP values were entered. Effective dose, collective effective dose, number of radiographs per year and the excess cancer risk arising from these radiographic examinations were then calculated. Discussion and Conclusion: Excess risk of fatal cancer due to x-ray examinations in the study population was calculated by collective effective dose. This risk in the population is about 0.42 cases suffering fatal cancer per year in this county. If the doses from other diagnostic radiology procedures, in which absorbed dose to patients are considerably higher than conventional radiography, are added to this amount, then the excess risk will be significantly greater than that obtained in this assessment.

Assessment of Extremely Low Frequency (ELF) Electric and Magnetic Fields in Hamedan High Electrical Power Stations and their Effects on Workers

Abstract: Introduction: Public and occupational exposure to extremely low frequency (ELF) electric and magnetic fields induced by electrical equipment is a significant issue in the environment and at the workplace due to their potential health effects on public health. The purpose of this study was assessment of the electric and magnetic fields intensities and determination of mental and psychological effects of occupational exposure in the high voltage electric power stations in the city of Hamadan, Iran. Material and Methods: The intensities of the magnetic and electric fields were measured at eight high voltage electric power stations at three different intervals of sources using an HI-3604 instrument. A two-part questionnaire was used to assess mental and psychological effects of the exposure to these fields. Two groups of control and case workers including 30 samples were selected to determine the exposure effects. Results: The results of field measurements showed the highest average electric field intensity was related to the CVT unit with 3110 V/m at a 2 m distance from the source and the lowest average was related to the control room with 1.35 V/m next to the source. Also, the highest and lowest magnetic field intensities were close to the transformator 2 and the battery room (50.42 and 1.31 mG), respectively. Discussion and Conclusion: The intensities of electric and magnetic fields in the selected stations are lower than the ACGIH and ICNIRP standard levels for occupational exposures. The results obtained indicate that the distribution of these fields was nonlinear around the sources and the effects observed on exposed workers were non-thermal.

CT-Based Brachytherapy Treatment Planning using Monte Carlo Simulation Aided by an Interface Software

Abstract: Introduction: In brachytherapy, radioactive sources are placed close to the tumor, therefore, small changes in their positions can cause large changes in the dose distribution. This emphasizes the need for computerized treatment planning. The usual method for treatment planning of cervix brachytherapy uses conventional radiographs in the Manchester system. Nowadays, because of their advantages in locating the source positions and the surrounding tissues, CT and MRI images are replacing conventional radiographs. In this study, we used CT images in Monte Carlo based dose calculation for brachytherapy treatment planning, using an interface software to create the geometry file required in the MCNP code. The aim of using the interface software is to facilitate and speed up the geometry set-up for simulations based on the patient’s anatomy. This paper examines the feasibility of this method in cervix brachytherapy and assesses its accuracy and speed. Material and Methods: For dosimetric measurements regarding the treatment plan, a pelvic phantom was made from polyethylene in which the treatment applicators could be placed. For simulations using CT images, the phantom was scanned at 120 kVp. Using an interface software written in MATLAB, the CT images were converted into MCNP input file and the simulation was then performed. Results: Using the interface software, preparation time for the simulations of the applicator and surrounding structures was approximately 3 minutes; the corresponding time needed in the conventional MCNP geometry entry being approximately 1 hour. The discrepancy in the simulated and measured doses to point A was 1.7% of the prescribed dose. The corresponding dose differences between the two methods in rectum and bladder were 3.0% and 3.7% of the prescribed dose, respectively. Comparing the results of simulation using the interface software with those of simulation using the standard MCNP geometry entry showed a less than 1% difference of the prescribed dose at 67% of the studied points (minimum <0.01%, maximum 4.8%). Discussion and Conclusions: Using the interface software reduces the overall simulation time. Comparison of the results of the measurements, simulation using the interface software and simulation using standard MCNP geometry entry shows that the use of tomographic images and transforming them into MCNP input file for dose calculation in brachytherapy is feasible and reasonably accurate.

Investigation of Anisotropy Caused by Cylinder Applicator on Dose Distribution around Cs-137 Brachytherapy Source using MCNP4C Code

Abstract: Introduction: Brachytherapy is a type of radiotherapy in which radioactive sources are used in proximity of tumors normally for treatment of malignancies in the head, prostate and cervix. Materials and Methods: The Cs-137 Selectron source is a low-dose-rate (LDR) brachytherapy source used in a remote afterloading system for treatment of different cancers. This system uses active and inactive spherical sources of 2.5 mm diameter, which can be used in different configurations inside the applicator to obtain different dose distributions. In this study, first the dose distribution at different distances from the source was obtained around a single pellet inside the applicator in a water phantom using the MCNP4C Monte Carlo code. The simulations were then repeated for six active pellets in the applicator and for six point sources. Results: The anisotropy of dose distribution due to the presence of the applicator was obtained by division of dose at each distance and angle to the dose at the same distance and angle of 90 degrees. According to the results, the doses decreased towards the applicator tips. For example, for points at the distances of 5 and 7 cm from the source and angle of 165 degrees, such discrepancies reached 5.8% and 5.1%, respectively. By increasing the number of pellets to six, these values reached 30% for the angle of 5 degrees. Discussion and Conclusion: The results indicate that the presence of the applicator causes a significant dose decrease at the tip of the applicator compared with the dose in the transverse plane. However, the treatment planning systems consider an isotropic dose distribution around the source and this causes significant errors in treatment planning, which are not negligible, especially for a large number of sources inside the applicator.

Attenuation Correction in SPECT during Image Reconstruction using an Inverse Monte Carlo Method: A Simulation Study

Abstract: Introduction: The main goal of SPECT imaging is to determine activity distribution inside the organs of the body. However, due to photon attenuation, it is almost impossible to do a quantitative study. In this paper, we suggest a mathematical relationship between activity distribution and its corresponding projections using a transfer matrix. Monte Carlo simulation was used to find a precise transfer matrix including the effects of photon attenuation. Material and Methods: List mode output of the SIMIND Monte Carlo simulator was used to find the relationship between activity distribution and pixel values in projections. The MLEM iterative reconstruction method was then used to reconstruct the activity distribution from the projections. Attenuation-free projections were also simulated. Reconstructed images from these projections were used as reference images. Our suggested attenuation correction method was evaluated using three different phantom configurations: uniform activity and uniform attenuation phantom, non-uniform activity and non-uniform attenuation phantom, and NCAT torso phantom. The mean pixel values and fits between profiles were used as quantitative parameters. Results: Images free from attenuation-related artifacts were reconstructed by our suggested method. A significant increase in pixel values was found after attenuation correction. Better fits between profiles of the corrected and reference images were also found for all phantom configurations. Discussion and Conclusion: Using a Monte Carlo method, it is possible to find the most precise relationship between activity distribution and its projections. Therefore, it is possible to create mathematical projections that include the effects of attenuation. This helps to have a more realistic comparison between mathematical and real projections, which is a necessary step for image reconstruction using MLEM. This results in images with much better quantitative accuracy at a cost of computation time and memory.

Extraction of the Longitudinal Movement of the Carotid Artery Wall using Consecutive Ultrasonic Images: a Block Matching Algorithm

Abstract: Introduction: In this study, a computer analysis method based on a block matching algorithm is presented to extract the longitudinal movement of the carotid artery wall using consecutive ultrasonic images. A window (block) is selected as the reference block in the first frame and the most similar block to the reference one is found in the subsequent frames. Material and Methods: The program was applied to the common carotid artery of ten healthy subjects and the longitudinal movement of the arterial wall was extracted in three cardiac cycles. Manual measurements were carried out to validate the automatic method. The maximum, minimum and average longitudinal displacements of the arterial wall were extracted from the automatic method and compared with the manual measurements, with 10 mm displacement of two blocks in first frame. Results: Paired t-test analysis showed no significant differences between the automatic and manual methods (p>0.05). There was significant correlation between the changes in the instantaneous longitudinal movement of the common carotid artery measured with the manual and automatic methods (correlation coefficient 0.97, p<0.05). Bland-Altman analysis with the agreement region of 0.03 to 0.17 mm and difference average of 0.10±0.03 mm indicated good agreement of the two methods. Discussion and Conclusion: This study shows that the block matching algorithm can automatically extract the longitudinal movement of the arterial wall from consecutive ultrasonic images.

Dosimetry Comparison of Water Phantom and Complete Eye Definition for 125I and 103Pd Brachytherapy Plaques

Abstract: Introduction: In this paper, by complete definition of human eye containing the various parts and their materials, the difference between this model and a homogeneous water phantom are compared for two ophthalmic plaques using 125I and 103Pd. Material and methods: The simulation of the two phantoms were performed in the MCNP-4C code and by using the geometry of a three-dimensional eye, different parts of the eye including the lens, cornea, retina, choroid, sclera, anterior chamber, optic nerve and tumor were defined in the eye phantom. Also, for two ophthalmic brachytherapy sources, 20 mm COMS plaques containing 24 125I or 103Pd sources were simulated. The depth dose and doses in different parts of the eye were calculated by using the *F8 tally in the MCNP code. Results: The results showed that the doses in different parts of the eye in the two phantoms were different and depended on the ophthalmic plaques. The dose increased in the tumor and decreased in some parts of the eye such as the lens. Discussion and Conclusion: Complete definition of human eye in simulation of ophthalmic brachytherapy leads to better results. As the effects of eye definition are different in the tumor and healthy tissues, the results for the eye phantom provide more accurate information for calculation of treatment time and the type of ophthalmic brachytherapy used.

Hyperthermia Effects in the Presence of Gold Nanoparticles Together with Chemotherapy on Saos-2 Cell Line

Abstract: Introduction: Hyperthermia created by microwave (MW), infrared, ultrasound and other methods, is often utilized as an adjuvant to sensitize cancer cells to the effects of chemotherapy and radiation therapy. We investigated the efficacy of hyperthermia using MW in synergy with chemotherapy in the presence and absence and gold nanoparticles (GNPs). Material and Methods: After culturing and proliferation of the Saos-2 cell line derived from human osteogenic sarcoma, the cells were incubated at two concentrations of GNPs in two diameters of 20 and 40 nm and in the absence and presence of doxorubicin in different groups. Forty eight hours after irradiating the cells with MW up to a temperature of 42°C, cell survival rate was determined using the MTT method, in order to study the effectiveness of the therapeutic parameters. Results: Cell survival in the presence of GNPs was greater than 95%. After chemotherapy by doxorubicin with and without 40 nm GNPs, cell survival rates were determined as 62.8% and 37.1%, declining down to 17% and 4.1% respectively following the combined treatment with MW and chemotherapy in the presence of 20 and 40 nm GNPs. Discussion and Conclusions: GNPs did not induce any cytotoxicity by themselves; their presence along with MW provided a reduction in survival rate that was comparable in severity with the lethal effects of doxorubicin. MW hyperthermia with GNPs produced a higher treatment efficiency in comparison to similar groups in which GNPs were absent. The synergism observed between hyperthermia and chemotherapy was dependent in GNPs' size and concentration. This finding could be caused by increased uptake of doxorubicin by the cells in the presence of GNPs.

CYTOTOXICITY AND PHOTOTOXICITY OF CHLOROPHYLL A/HYDROXYPROPYL-γ-CYCLODEXTRIN COMPLEX ON LEISHMANIA MAJOR PROMASTIGOTES

Abstract: Introduction: Cutaneous leishmaniasis (CL) is a widespread disease that is epidemic in Iran, too. Photodynamic therapy (PDT) is an attractive modality to treat cancer and hyper proliferative diseases based on the use of a photosensitizer in the presence of oxygen and proper wavelength of light. In consideration of lesion location, lack of systemic involvement and inefficiency of current treatments, nowadays this modality is purposed for treating Leishmaniasis. In this paper, efficacy of PDT using a natural dye (chlorophyll a) on Leishmania major promastigotes is reported. Material and Methods: The experiments was done on Leishmania major parasites (MRHO/IR/75/ER) in the presence of Chlorophyll a /Hydroxypropyl-γ-cyclodextrin(chl a/CD) complex as a photosensitizer. At first, dye uptake by promastigotes was evaluated via fluorimetric assessments after different incubation periods. Then dye cytotoxicity was evaluated at different concentration after 24 h incubation. Finally PDT experiments were designed with two doses of light and 10 µM of photosensitizer. Considering all possible controls, the percentage of the parasite survival at 24 hours post treatment was assessed by MTS method. All experiments were repeated at least three times. Results: On the basis of the dye uptake data, 24h was considered for incubating of photosensitizer with promastigotes. IC50 of chl a/CD complex was about 42.6 µM. After parasites irradiation by light at 248 j/cm2, more than 50% of cell death was recorded that is significant in comparing with similar groups without dye, without light, and lower dose of light. In these conditions, ED50 of PDT on promastigotes is determined nearly 246 J/cm2. Discussion and Conclusion: Considering low cytotoxicity in darkness and adequate phototoxicity of chl a/CD complex in comparison with other photosensitizers such as AlPhtalocyanine chloride, it can be introduced as a promising candidate for futher use in PDT experiments on amastigotes and Leishmaniasis animal models.

Study of Optical Models Regarding the Human Eye

Abstract: Introduction: Until now, many models have been presented for optical study of the human eye. In recent years, surgery on the anterior section of the eye (such as cataract and photo-refractive surgery) has increased, so a study on the optics of the eye and evaluation of vision quality has become more important. Material and Methods: In this article, some of these models are considered. They include models with spherical and conic-section surfaces (for cornea and lens), simple models and new models with complex surfaces. Results: Evaluation of the optical models of the eye provides the possibility of enhancing the representation of human vision and also increasing the accuracy of surgery on the anterior section of the eye to enable higher quality vision.

Calculation of dose distribution in tongue brachytherapy by different radioisotopes using monte carlo simulation and comparison with experimental data

Abstract: Introduction: Among different kinds of oral cavity cancers, the frequency of tongue cancer occurrence is more significant. Brachytherapy is the most common method to cure tongue cancers. Long sources are used in different techniques of tongue brachytherapy. The objective of this study is to asses the dose distribution around long sources, comparing different radioisotopes as brachytherapy sources, measuring the homogeneity of delivered dose to treatment volume and also comparing mandible dose and dose of tongue in the regions near the mandible with and without using shield. Material and Method: The Monte Carlo code MCNP4C was used for simulation. The accuracy of simulation was verified by comparing the results with experimental data. The sources like Ir-192, Cs-137, Ra-226, Au-198, In-111 and Ba-131 were simulated and the position of sources was determined by Paris system. Results: The percentage of mandible dose reduction with use of 2 mm Pb shield for the sources mentioned above were: 35.4%, 20.1%, 86.6%, 32.24%, 75.6%, and 36.8%. The tongue dose near the mandible with use of shied did not change significantly. The dose homogeneity from the most to least was obtained from these sources: Cs-137, Au-198, Ir-192, Ba-131, In-111 and Ra-226. Discussion and Conclusion: Ir-192 and Cs-137 were the best sources for tongue brachytherapy treatment but In-111 and Ra-226 were not suitable choices for tongue brachytherapy. The sources like Au-198 and Ba-131 had rather the same performance as Ir-192

The Role of MRSI in Target Volume Definition for Radiation Therapy of Prostate Cancer

Abstract: Introduction: Recently, magnetic resonance spectroscopic imaging (MRSI), as a functional imaging method, has been used for clinical target volume definition. In this study, we used this method to define the target volume in prostate radiotherapy. Material and Method: In this study, we used images of 20 prostate cancer cases. MRSI and MRI images were fused with CT images. Then, treatment planning was preformed for each patient using three methods: CT, CT+MRI and CT+MRSI planning. Results: The volumes of MRICTV and MRIPTV were on average 12.83% and 8.97% lower than the corresponding CTCTV and CTPTV volumes, respectively. For MRSI, the CTV and PTV volumes were 21% and 27.41% greater than the corresponding CT-based volumes. Maximum dose to rectum showed a 0.58% increase in MRSI relative to CT, and 1.09% reduction in MRI relative to CT. Maximum dose variation in femoral heads showed a 5.4% increase in MRSI relative to CT and 0.67% reduction in MRI relative to CT. Discussion and Conclusion: Application of MRSI for target volume definition of prostate cancer leads to an increase in this volume in comparison to CT planning alone. In this imaging technique, protocol and resolution should be considered to determine the target volume exactly.