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Background: 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

Materials and Methods: 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.

Results : 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.

Conclusion : The optimum member of every filter’s family was obtained. Iran . J. Radiat. Res., 2004 1(4): 205-210

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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

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Background:

An effective method for management of large and bulky malignant tumors. This treatment modality is also known as Specially Fractionated Radiation Therapy (SFRT). In this treatment technique a grid block converted the open radiation field into a series of pencil beams. Dosimetric characteristics of an external beam grid radiation field have been investigated using experimental and Monte Carlo simulation technique.

Grid radiation therapy, using the megavoltage X-ray beam, has been proven to be

Materials and Methods:

radiation field have been determined using experimental and Monte Carlo simulation technique, for 6- and 18 MV X-ray beams from a Varian Clinics 2100C/D. The measurements were performed using LiF TLD and film in Solid Water phantom Material. Moreover, the MCNP Monte Carlo code was utilized to calculate the dose distribution in the grid radiation field in the same phantom material. The results of the experimental data were compared to the theoretical values, to validate this technique. Upon the agreement between the two techniques, dose distributions can be calculated for the grid field with different patterns and sizes of holes, in order to find an optimal design of the grid block.

Dose distributions (%DD as well as the beam profiles) of a grid

Results:

simulation technique was in good agreement with the measured data. In addition, the 3D dose distribution of the grid field generated by the Monte Carlo simulation gave more detailed information about the dose pattern of the grid.

The results of dose profiles for 6 MV X-ray beams obtained with the Monte Carlo

Conclusion:

Carlo simulation technique can be utilized to optimize the pattern, size and spacing between the holes, for optimal clinical results.

The grid block can be used as a boost for treatment of bulky tumors. The MonteIran. J. Radiat. Res., 2005 2 (4): 167-174

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ABSTRACT

Background:

for treatment verification in radiation therapy. Several physical characteristics of Scanning

Liquid filled Ionization Chamber EPID (SLIC-EPID) including: extra build-up layer,

reproducibility and uniformity, and noise level were investigated.

Electronic Portal Imaging Devices (EPIDs) have found an outstanding position

Materials and Methods:

equilibrium, 1-30 mm white water materials (RW3) were placed on the EPID cover and the

variation of pixel values were investigated. To assess the short term reproducibility, a series of

10 consecutive Electronic Portal Images (EPIs) were acquired. The variation of pixel values

were then determined in irradiated field using MATLAB software. For long term reproducibility,

the described above experiment was then repeated seven times. To determine the noise level

in EPID images, 10 consecutive flood images were acquired. The measurement was repeated

after two days during a fortnight.

To determine the extra build-up layer to reach the electronic

Results:

No significant variation was observed between the maximum thickness of build-up layer

required for the central axis and peripheral points. For reproducibility measurements, no systematic

variation was observed between mean, maximum and minimum acquired pixel values.

Both the long-term and short term reproducibility was found to be less than 1%. The noise level

was generally less than 1% and this can be referred as an acceptable dose level

5 mm of RW3 material was found to increase the pixel values to the maximum possible..

Conclusion:

can be used for dosimetry. However, for a particular linac energy and EPID image acquisition

mode, the extra build-up layer thickness must be known for the EPID to be used for dosimetric

purposes

The physical characteristics, measured in this work, suggest that the SLIC-EPID. Iran. J. Radiat. Res., 2005 2 (4): 175-183

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ABSTRACT

Background: Although Electronic Portal imaging Devices (EPIDs) have originally developed for positioning verification, they can also be used for dosimetric purposes. In the current work, the dose response of minimum detectable thickness of a Scanning Liquid filled Ion Chamber EPID, SLIC-EPID, and the variation of transmitted dose with the shift of inhomogeneity inside of phantom was also evaluated were investigated.

Materials and Methods: The SLIC-EPID pixel values were converted to the dose values using ionization chamber calibration and KODAK Extended Dose Range films (EDR2 films). The variation of EPID dose values with phantom thickness was investigated. In order to find the rate of dose deposited per centimetre of phantom, several reference points were defined and the variation of dose delivered to the points in the vicinity of reference points was investigated. Two cm thick foam layer, as air gap, was shifted in the beam direction to evaluate the variation of transmitted dose with the shift of inhomogeneity position inside of phantom.

Results: An exponential decrease of the transmitted dose values was observed with the increase of the thickness of attenuators. The maximum and minimum rate of dose deposited per unit of phantom thickness was found to be 5.45% /cm and 3.78% /cm, respectively. Due to the reproducibility and noise level of SLIC-EPID, a 0.5 cm of thickness can be detected with a good reliability. The relative error of EPID dose values increases with an increase of phantom thickness for both data sets. The relative error did not exceed 0.7%. No significant variation in transmitted dose inplane and crossplane profiles were found with the shift of inhomogeneity in the beam direction.

 Conclusion: The minimum detectable thickness is an important factor to evaluate an imager for dosimetric purposes. The SLIC-EPID can be used as a reliable two-dimensional dosimeter.

 

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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.

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Background: Study of vascular and its secretory profile changes is an important issue in pathogenesis of radiation myelopathy. This paper reports the prostacyclin concentration changes after low-moderate doses of X-irradiation within a short period of time. Materials and Methods: Cervical cords of Wistar rats were irradiated to doses of 0.5, 1, 2, 4 and 6 Gy X-rays. After 24 hours, 2 and 13 weeks post-irradiation, prostacyclin contents were quantified and cords specimens were also stained routinely for histological studies. Results: Twenty four hours post-irradiation, showed a decrease in the content of prostacyclin after doses of 0.5 and 1 Gy 91.67±1.47% 96.80±2.17% of respectively age-matched control group. After 2 weeks the concentration of prostacyclin showed significant decreases after 6 Gy. After 13 weeks irradiation shows marked differences even after a small dose of 2 Gy (p<0.001), and after doses of the low dose group. The differences between concentration values at doses of 4 Gy and 6 Gy were significant in comparison with the control (p<0.001 and p<0.002, respectively). Conclusion: Results suggested that the response of the vascular tissues to low and moderate doses of radiation occurs prior to that of the nervous tissue of the spinal cord. It means that the asymptomatic interval after radiation is characterized by sequential physiological changes which are imperfectly reflected in routine histological study and that even in the histologically unaffected spinal cord severe impairment is present in substructures and biochemistry of irradiated spinal cord.

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Background: In the present investigation radiation and cadmium induced biochemical changes in the kidney of Swiss albino mice have been studied. Materials and Methods: For this purpose, adult male Swiss albino mice (6-8 weeks old) were divided into four groups. Group I (sham-irradiated), Group II (treated with CdCl2 solution 20 ppm), Group III (irradiated with 1.25, 2.5 and 5.0 Gy gamma rays), Group IV (both irradiated with 1.25, 2.5 and 5.0 Gy gamma rays and treated with CdCl2 solution). The animals were autopsied after 1, 2, 4, 7, 14 and 28 days of treatment. The kidney was taken out and different biochemical parameters, such as total proteins, glycogen, cholesterol, acid phosphatase activity, alkaline phosphatase activity, DNA and RNA were estimated. Results: In irradiated animals, the values of total proteins, glycogen, acid phosphatase, alkaline phosphatase activity and RNA increased continuously up to day-7 and decreased thereafter up to day-28. The changes were dose dependent. In CdCl2 treated animals, the values of glycogen and total proteins decreased during the early intervals and increased thereafter whereas the values of acid and alkaline phosphatase activity and RNA increased during early intervals and decreased thereafter. The values of cholesterol and DNA showed decrease in all the experimental groups (except group I) up to day-7 and increase thereafter up to day-28. After combined treatment also, the parameters followed the same pattern of increase and decrease, but the changes were more pronounced indicating their synergistic effect. The biochemical parameters showed highly significant values (P<0.001) as compared to normal ones. Conclusion: These results indicate that combined treatment of cadmium and gamma radiations causes synergistic or additive effect.

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Background: The presence of small intestine in the radiation field during pelvic cancers treatment causes an interruption in radiotherapy. A non-invasive method was developed to exclude small intestine during conventional radiotherapy. Materials and Methods: The incidence of the radiation therapy interruption is highly dependent upon the area of the small intestine included in the portals and its absorbed dose. In order to investigate the radiation therapy interruption and the resulting elongation of the total treatment time, 35 patients suffering from pelvic cancers were selected and randomly assigned to control and study groups. All the patients were treated in prone position. In the 18 patients in the study group, a commercially available water bag was inserted between patient abdomen and treatment couch. Other 17 patients in the control group underwent similar therapy without water bag. Results: The total treatment time was shown to be 1.52 days shorter in the study group with a statistically significant difference (p<0.003). Conclusion: Due to the lack of the early morbidities during radiotherapy, it is concluded that the current method helps to optimize total treatment time by preventing interruption of radiation therapy.

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Background: High level radiation areas have been recognized on various parts of the earth. Mahallat hot spring region is one of these areas. Study of exposure in these areas can be helpful in investigating the effects of ionizing radiation. Internal and external exposure to the staff was studied. Materials and Methods: Used materials and instruments include: RSS-112 ionizing chamber for environmental gamma rays measurement, pure germanium detector for measuring radioactive elements in the ground, liquid scintillation counter for measuring 222Rn gas concentration in water samples, Bubbler chamber and Locus cells for 226Ra concentration measurements as emanation method and Alfa guard detector for 222Rn concentration measurements. Results: Considering stay period of the studied groups in indoor and outdoor environment, calculated annual external effective dose for staff has been 514.8 ± 22.7 μSv. Annual internal effective doses for staff in outdoor and indoor environment has been 21.1 mSv. Annual internal effective dose for staff due to drinking water has been 32 μSv. Conclusion: Measurements showed that more than 90% of the received dose in the studied groups was due to inhalation of Radon gas. External and internal effective dose for the staff was 21.6 mSv. Considering these results Mahallat hot spring region is a high level natural radiation area (HLNRA). Iran. J. Radiat. Res., 2008 6 (1): 13-18