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Showing 142 results for Le
H. Samavat, M. R. D. Seaward, D. H. Gonzales, Gh. Azizian,
Volume 1, Issue 4 (3-2004)
Abstract
Background: 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. Materials and Methods: 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. Results: 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. Conclusion: The overall conclusion is that the frequency of chromosomal damage in both groups of radiographers did not exceed that of the control group. Iran . J. Radiat. Res., 2004 1(4): 195-198
P. Abdolmaleki, M. Yarmohammadi, M. Gity,
Volume 1, Issue 4 (3-2004)
Abstract
Background: We designed an algorithmic model based on the logistic regression analysis and a non-algorithmic model based on the Artificial Neural Network (ANN). Materials and methods: 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. Results: 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%. Conclusion: 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. Iran . J. Radiat. Res., 2004 1(4): 217-228
P. Abdolmaleki, M. Mokhtari Dizaji, M.r. Vahead, M. Gity,
Volume 2, Issue 1 (6-2004)
Abstract
Background: Logistic discriminant method was applied to differentiate malignant from benign in a group of patients with proved breast lesions on the basis of ultrasonic parameters. Materials and Methods: Our database include 273 patients' ultrasonographic pictures consisting of 14 quantitative variables. The measured variables were ultrasound propagation velocity, acoustic impedence and attenuation coefficient at 10 MHz in breast lesions at 20, 25, 30 and 35 º C temperature, physicsl density and age. This database was randomly divided into the estimation of 201 and validation of 72 samples. The estimation samples were used to build the logistic
discriminant model, and validation samples were used to validate the performance. Finally,
important criteria such as sensitivity, specificity, accuracy and area under the receiver operating characteristic curve (ROC) were evaluated. Results: Our results showed that the logistic discriminant method was able to classify correctly 67 out of 72 cases presented in the validation sample. The results indicate a remarkable
diagnostic accuracy of 93%. Conclusion: A logistic discriminantor approach is capable of predicting the probability of malignancy of breast cancer. Features extracted from ultrasonic measurement on ultrasound imaging is used in this approach. Iran . J. Radiat. Res., 2004 2 (1): 27-34
H. Nedaie, M. Shariary, H. Gharaati, M. Allahverdi, M.a. Mosleh-Shirazi,
Volume 2, Issue 4 (3-2005)
Abstract
ABSTRACT Background: accurate methods of radiation therapy dose calculation. There are different Monte Carlo codes for simulation of photons, electrons and the coupled transport of electrons and photons. MCNP is a general purpose Monte Carlo code that can be used for electron, photon and coupled photon-electron transport. Monte Carlo simulation of radiation transport is considered to be one of the mostMaterials and Methods: calculating electron beam doses in water. For simulating, the geometry and other parameters were the same for three codes. By choosing two energy indexing algorithm (ITS & MCNP), absorbed doses were scored in water. 10 In this study the MCNP4A, 4B and 4C have been compared when6 Particles were followed in these three cases.Results: used in 4B and 4C versions. There was a good agreement between versions 4B and 4C. For the energy spectrum, there were significant differences between these three versions in two planes. MCNP4C and 4B gave different results compared to 4A when the ITS algorithm wasConclusion: for electron transport and also requires a shorter time than the two previous versions. These results, in addition to the practical measurements acquired with MCNP4B by other investigators, suggest that in electron transport the user should use the ITS indexing energy algorithm. Because of new improvements in electron transport in 4C, this version is reliableIran. J. Radiat. Res., 2005 2 (4): 191-195Keywords: Radiotherapy, electron therapy, Monte Carlo, absorbed dose, energy spe
V. Changizi, M.a. Oghabian, S. Sarkar, R.d. Speller, A. Arab Kheradmand,
Volume 2, Issue 4 (3-2005)
Abstract
ABSTRACT Background: Coherent scattering leads to diffraction effects and especially constructive interferences. These interferences carry some information about the molecular structure of the tissue. As breast cancer is the most widespread cancer in women, this project evaluated the application of small angle X-ray scattering (SAXS) for differentiation between normal and cancerous breast tissues. Small angle X-ray scattering (to angles less than 10°) is predominantly coherent.Materials and Methods: primary collimator, sample holder, secondary collimator and HP Ge detector was used. The best constructive interference was found to be at 6.5 at several angles of 4, 5, 6, 6.5 and 7.3 degrees. The total number of 99 breast tissue samples, including normal and tumor were studied at the 6.5 transfer was obtained for each sample. The energy dispersive method with a set up including X-ray tube,° after doing experiments on adipose breast tissue°. The corrected intensity versus momentumResults: adipose tissue and mixed tissue (adipose & fibroglandular) from tumor in peak positions (each coherent scattering spectrum has a peak that its position is determined by momentum transfer). Furthermore adipose tissue has shown significantly higher peaks than other breast tissues. Benign and malignant breast tissues were differentiated by both peak positions and peak heights (each peak has a height in coherent scattering spectrum). Preservation of samples nitrogen tank had no effects on molecular structure of the breast tissue. Adipose tissue shows a sharp peak in low momentum transfer region. It is easy to separateConclusion: between normal, benign and malignant breast tissues. By energy dispersive small angle X-ray scattering, it is possible to differentiateIran. J. Radiat. Res., 2005 2 (4): 205-210
P. Abdolmaleki, H. Abrishami-Moghddam, M. Gity, M. Mokhtari-Dizaji, A. Mostafa,
Volume 3, Issue 3 (12-2005)
Abstract
ABSTRACT Background: 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. Materials and Methods: 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. Results: 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). Conclusion: An ANN supported by wavelet transform can be trained to differentiate malignant from benign breast tumors with a reasonable degree of accuracy.
Dr. M.a. Mosleh-Shirazi, H. Taylor, A.p. Warrington, F.h. Saran,
Volume 4, Issue 1 (Summer 2006)
Abstract
Background: In order to assign appropriate planning target volume (PTV) margins, each centre should measure the patient positioning deviations for their set-up techniques. At the Royal Marsden Hospital, UK, a conformal shell (cast) system is used when a stereotactic frame is not suitable. In this paper, we report on a series of measurements with the aim of obtaining the systematic and random components of positioning error when using the above-mentioned shell system. Materials and Methods: The verification protocol was based on orthogonal pairs of anterior-posterior and lateral electronic portal images (EPIs) used to check the isocentre position. The isocentre verification results of paediatric patients were analysed. A practical ‘off-line’ patient set-up correction strategy had been used with the aim of reducing systematic errors. The verification protocol involved EPI acquisition on the first three fractions and then on a weekly basis. Additional images were taken if an isocentre movement was applied based on a 3 mm tolerance for a consistent 1D discrepancy. Results: Four patients required isocentre corrections ranging between 2 mm and 4 mm. Following the off-line corrections, the residual systematic errors in each direction were within 0.5 mm while the 1D random variation was about 1.0 mm. Conclusions: The head fixation system in conjunction with the correction strategy successfully kept the random and systematic positioning errors within an acceptable level well within the 3 mm tolerance. The measured components of positioning error can be used to define appropriate PTV margins.
Dr. A.a. Mowlavi, A. Binesh, H. Moslehitabar,
Volume 4, Issue 1 (Summer 2006)
Abstract
Background: Palladium-103 (103Pd) is a brachytherapy source for cancer treatment. The Monte Carlo codes are usually applied for dose distribution and effect of shieldings. Monte Carlo calculation of dose distribution in water phantom due to a MED3633 103Pd source is presented in this work.
Materials and Methods: The dose distribution around the 103Pd Model MED3633 located in the center of 30×30×30 cm3 water phantom cube was calculated using MCNP code by the Monte Carlo method. The percentage depth dose (PDD) variation along the different axis parallel and perpendicular to the source was also calculated. Then, the isodose curves for 100%, 75%, 50% and 25% PDD and dosimetry parameters of TG-43 protocol were determined.
Results: The results show that the Monte Carlo Method could calculate dose deposition in high gradient region, near the source, accurately. The isodose curves and dosimetric characteristics obtained for MED3633 103Pd source are in good agreement with published results.
Conclusion: The isodose curves of the MED3633 103Pd source have been derived form dose calculation by MCNP code. The calculated dosimetry parameters for the source agree quite well with their Monte Carlo calculated and experimental measurement values.
Dr Mohammad Amin Mosleh-Shirazi,
Volume 4, Issue 2 (9-2006)
Abstract
ABSTRACT
Intracranial tumours often require radiotherapeutic approaches that differ from other sites. Their specific requirements merit a specialized discussion. A brief review of radiotherapy techniques to treat intracranial tumours is presented with emphasis on the author’s own experience and work, where appropriate. A clinical introduction is presented first followed by a description of both conventional and modern techniques. Examples from clinical practice are also given. The issues discussed include direct simulation, 2D and 3D treatment planning, the use of CT and other imaging modalities, field shaping and non-coplanar techniques. In the modern radiotherapy era, simple conventional techniques still have a role to play in routine clinical practice. As new technologies are introduced into relatively under-resourced centres, they should be used judiciously and appropriately to maximize benefit to the whole patient population.
Dr. S.m.j. Mortazavi, M.a. Mosleh-Shirazi, M.r. Maheri, H. Yousefnia, S. Zolghadri, A. Haji-Pour,
Volume 5, Issue 3 (12-2007)
Abstract
Background: In megavoltage radiotherapy rooms, ordinary concrete is usually used due to its low construction costs, although higher density concrete are sometimes used, as well. The use of high-density concrete decreases the required thickness of the concrete barrier hence, its disadvantage is its high cost. In a nuclear reactor, neutron radiation is the most difficult to shield. A method for production of economic high-density concrete with appropriate engineering properties would be very useful. Materials and Methods: Galena (PbS) mineral was used to produce of a high-density concrete. Galena can be found in many parts of Iran. Two types of concrete mixes were produced. The water-to-concrete (w/c) ratios of the reference and galena concrete mixes were 0.53 and 0.25, respectively. To measure the gamma radiation attenuation of Galena concrete samples, they were exposed to a narrow beam of gamma rays emitted from a cobalt-60 therapy unit. Results: The Galena mineral used in this study had a density of 7400 kg/m3. The concrete samples had a density of 4800 kg/m3. The measured half value layer thickness of the Galena concrete samples for cobalt- 60 gamma rays was much less than that of ordinary concrete (2.6 cm compared to 6.0 cm). Furthermore, the galena concrete samples had significantly higher compressive strength (500 kg/cm2 compared to 300 kg/cm2). Conclusion: The Galena concrete samples made in our laboratories had showed good shielding/engineering properties in comparison with all samples made by using high-density materials other than depleted uranium. Based on the preliminary results, Galena concrete is maybe a suitable option where high-density concrete is required in megavoltage radiotherapy rooms as well as nuclear reactors.
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