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Background: Annual patient effective dose equivalent can be considered as a quantitative physical parameter describing the activities performed in each nuclear medicine department. Annual staff dose equivalent could be also considered as a parameter describing the amount of radiation risk for performing the activities. We calculated the staff to patient dose equivalent ratio to be used as a physical parameter for quantification of ALARA law in nuclear medicine departments.

Materials and Methods: As a part of nationwide study, this paper reports the staff and patient absorbed dose equivalents from diagnostic nuclear medicine examinations performed in four nuclear medicine departments during 1999-2002. The type and frequency of examinations in each department were determined directly from hospital medical reports. Staff absorbed dose equivalents were calculated from regular personal dosimeter reports.

Results: The total number of examinations increased by 16.7% during these years. Annual
patient collective dose equivalent ( EDE ) increased about 13.0% and the mean effective dose equivalent per exam was 3.61±0.07 mSv. Annual total staff absorbed dose equivalent (total of 24 radiation workers) in four departments increased from 40.45 mSv to 47.81 mSv during four years that indicates an increase of about 20.6%. The average of annual ratios of staff to patient effective dose equivalents in four departments were 1.83×10^-3, 1.04×10^-3, 3.28×10^-3 and 3.24×10^-3, respectively, within a range of 0.9×10^-3 – 4.17×10^-3 . The mean value of ratios in four years was about 2.24×10^-3 ± 1.09×10^-3 that indicates the staff dose of about two 1000th of
patient dose.

Conclusion: The mean value of ratios in four years was about 1.89×10^-3 ± 0.95×10^-3 indicating the staff dose of about one 1000th of the patient dose. The staff to patient absorbed dose equivalent ratio could be used as a quantitative parameter for describing ALARA law in radiation protection and risk-benefit assessments. Iran . J. Radiat. Res., 2004 2 (2): 63-68

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ABTRACT

Background: In nuclear medicine, phantoms are mainly used to evaluate the overall performance of the imaging systems and practically there is no phantom exclusively designed for the evaluation of the software performance.  In this study the Hoffman brain phantom was used for quantitative evaluation of reconstruction techniques. The phantom is modified to acquire tomographic and planar image of the same structure. The planar image may be used as the reference image to evaluate the quality of reconstructed slices using the companion software developed in MATLAB.

Methods and Materials: The designed phantom is composed of 4 independent 2D slices that may be placed juxtapose to form the 3D phantom. Each slice is composed of objects of different size and shape e.g. circle, triangle, and rectangle. Each 2D slice was imaged at the distances from 0 to 15 cm from the collimator surface. The phantom in 3D configuration was imaged acquiring 128 views of 128×128 matrix size. Reconstruction was performed using different filtering condition and the reconstructed images were compared to the corresponding planar images. The modulation transfer function, scatter fraction and attenuation map were calculated for each reconstructed image

Results: Since all the parameters of the acquisition were identical for the 2D and the 3D imaging. It was assumed that the difference in the quality of the images was exclusively due to reconstruction condition. The planar images were assumed to be the most perfect images that could be obtained with the system. Comparing the reconstructed slices to the corresponding planar images yielded the optimum reconstruction condition.  The results clearly showed that Wiener filter yields superior quality image among the entire filter tested. The extent of the improvement has been quantified in terms of universal image quality index.

Conclusion: The phantom and the accompanying software were evaluated and found to be quite useful in determining the optimum filtering condition and mathematical evaluation of the scatter and attenuation in tomographic images.

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Background: The purpose of this study was to evaluate the dependency of MAGICA polymer gel dosimeter response (R2) on different electron energies as well as on different mean dose rate for a standard clinically used linear accelerator. Materials and Methods: The sensitivity of the dosimeter was represented by the slope of calibration curve in the linear region measured for each modality. A calibration curve (in the linear region) based on 12 dosimeters (11 irradiated and one blank) was obtained for 6 MeV electron beam. Dosimeter energy dependence was studied for electron energies of 4,6,12 and 18 MeV. Dose rate dependence was studied in 10 MeV electron beam with the use of dose rates 80,160,240,320,400 and 480 cGymin-1. Evaluations of dosimeters were performed on Siemens Symphony, Germany, 1.5T Scanner in the head coil. A multiecho sequence with 32 equidistant echoes was used for the evaluation of irradiated polymer gel dosimeters. The parameters of the sequence were as follows: TR 3000ms, TE 20ms, Slice Thickness 4mm and FOV 256mm. Results: Polymer gel dosimeter response R2 was increased with increasing electron energy. No trend in polymergel dosimeter R2 dependence was found on mean dose rate for electron beams. Conclusion: In MAGICA polymer gel, the sensitivity is dependant on electron energy increase, but no dependence was observed on response to dose rate. The presence of antioxidant and oxygen scavengers in the MAGICA polymer gel is believed to cause different results. Iran. J. Radiat. Res., 2008 6 (1): 31-36

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Background: Since 1996 the assessment of environmental gamma radiation dose in residential areas of Iranian towns and cities has been accomplished for 10 counties. As a practical method and based on the results of a pilot study, in order to attribute the final results to the whole residential area of a town five stations were selected for every town. The location of individual station was studied closely to comply with recommended conditions in the literature. Materials and Methods: RDS-110 was employed to measure gamma dose rate for one hour. Average annual dose rates plus conversion coefficients were employed to estimate gonad, bone marrow, equivalent and effective dose. Result: Minimum and maximum annual bone marrow and gonad dose equivalent attributed to environmental gamma are 0.24 mSvy-1 (for both tissues) and 1.44 and 1.46 mSvy-1, respectively. Conclusion: Average gonad and bone marrow doses for North Khorasan, Boshehr and Hormozgan provinces were less than the corresponding values for normal area. Iran. J. Radiat. Res., 2009 7 (1): 41-47

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Background: A variable resolution X-ray (VRX) CT scanner provides a great increase in the spatial resolution. In VRX CT scanners, the spatial resolution of the system and its field of view (FOV) can be changed according to the object size. One of the main factors that limit the spatial resolution of VRX CT scanner is the effect of the X-ray focal spot. Materials and Methods: A theoretical study of the effect of X-ray focal spot on the spatial resolution of VRX CT is presented in this paper. In this study, we used the parameters of an actual VRX CT scanner. By using the relevant equations, the effects of foal spot sizes of 0.6 and 0.1 mm were calculated on spatial resolution of the system at various opening half angles. Results: Focal spot size of 0.6 mm had no significant effect on spatial resolution of the system for opening half angles of above 14°. Even focal spot sizes of larger than 0.6 mm could not affect the spatial resolution of the system. For opening half angles of below 14°, foal spot size of 0.6 mm limited the spatial resolution of the system to 5.7 cycle/mm and caused great spatial resolution non-uniformity along the detector length. Conclusion: By focal spot size of 0.1 mm, the spatial resolution varied as a function of the opening half angle and increased to more than 30 cycle/mm. Additionally, focal spot size of 0.1 mm minimized the spatial resolution non-uniformity along the detector length. Iran. J. Radiat. Res., 2010 8 (1): 37-43

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Background: Tangential irradiation of intact breast is one of the most common procedures performed in any radiotherapy center. This method is performed by using 2D and 3D treatment planning. The aim of this study was to compare 2D with 3D plans in breast conserving radiotherapy. Homogeneity of isodose, and lung received dose were compared. Materials and Methods: Twenty patients with breast cancer undergoing lumpectomy were included in this study. Two dosimetry plans were generated for each patient. The first plan was performed on one CT-slice (central) by using Eclipse-TPS. The second plan was based on full CT-slices using the same TPS. For both plans, the volumes receiving lower than 95% (cold areas), greater than 105% (hot areas) of the reference dose and the volume of lung receiving ≥30Gy (Vol≥30Gy) were derived from dose volume histogram (DVH). All calculations were done for 6MV photon beams. Results: By the 2D plans, the mean values of cold and hot areas were 26.4% and 8.1%, respectively. These values were reduced to 18.9% and 6.9% in 3D plans, respectively (p<0.000, p<0.01). Dose homogeneity was obtained 65.4% in the 2D and improved to 74.8% in the 3D plans (P<0.000). By the use of 3D plans, received dose within lung volume was decreased to 6.7% as compared with 8.9% of 2D plans (P<0.01). Conclusion: Application of 3D plans can lead to a more tumor control probability and cosmetic results, but less skin and lung side effects in patients with conserved breast. Iran. J. Radiat. Res., 2011 9(2): 121-125

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Background: Craniospinal radiotherapy faces technical challenges which are due to the sensitivity of the location in which the gross tumor is, and to organs at risk around planning target volume. Using modern treatment planning systems causes a reduction in the complexities of the treatment techniques. The most effective method to assess the dosimetric accuracy and the validity of the software used for treatment planning is to investigate the radiotherapy and treatment planning by means of a anthropomorphic Rando phantom which was used here for treatment planning and practical dosimetry for craniospinal radiotherapy. Studying the absorbed dose by the organs at risk was the secondary objective discussed in this paper. Materials and Methods: Treatment planning in craniospinal radiotherapy was done using CorePlan 3D treatment planning software. Radiotherapy was administered on a anthropomorphic Rando phantom and practical dosimetry was done using GR-200 TLDs. Varian Clinac 2100C/D was used for radiotherapy. Results: The absorbed dose by regions of interest was separately calculated for treatment planning and radiotherapy. Except the conjunction areas of the cranial and spinal radiation fields, the difference among the results was not more than 5%. Full comparison of the results for each part has been presented. Conclusion: The comparison the results of practical dosimetry and treatment planning software supports the validity of CorePlan treatment planning system. Also analysis of the absorbed dose through organs at risk showed that the absorbed dose by organs at risk have an acceptable value with respect to tolerance dose of these organs. The only unacceptable result was related to thyroid. Iran. J. Radiat. Res., 2011 9(3): 151-158

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Background: The aim of this work was to establish how well gel dosimeters performed, as substitutes for brain tissue compared with standard phantom materials such as water, polymethyl-methacrylate (or PMMA), A150 plastic and TE- liquid phantom material for dosimetry of neutron beams in boron neutron capture therapy. Materials and Methods: Thermal neutron fluence, photon dose and epithermal neutron dose distributions were computed for the epithermal neutron beam of the optimized linac based BNCT. Results: Amongst all investigated phantom materials, TE-liquid was shown to be a better substitute for brain tissue than other phantom materials. The differences between TE- liquid and brain at the depth of 6.1 cm for thermal neutron fluence, gamma dose and epithermal neutron dose distributions was calculated 2.80%, 2.40% and -13.87% , respectively. In comparison with the other gel dosimeters, LMD2 provided a better simulation of radiation transport in the brain. It's results differed from the real brain, at the depth of 6.1 cm, for thermal neutron fluence, gamma dose and epithermal neutron dose distributions, by -1.27%, 4.20% and 21.05% respectively. Conclusion: Even though, in gamma dose distribution the LMD2 has large deviation from brain tissue distribution, the deviation is approximately independent of depth, so the results can be multiplied by a constant coefficient to be more consistent with reality. Even though, TE- liquid showed satisfactory results for brain tissue substitution in BNCT, but some properties of gel dosimeters such as three dimensionality, make LMD2 a potentially good dosimeter for dosimetric verification in BNCT.

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Background: High density concrete is extensively used for efficient radiation attenuation in radiotherapy rooms and nuclear reactors. Over the past eight years, some efficient galena-based concrete samples for shielding X or gamma rays was produced. The goal of this study was to produce a novel high density concrete against neutron and photon radiations using tourmaline and galena. Materials and Methods: Attenuation of gamma photons was measured using a Farmer type ionization chamber with a standard ⁶⁰Co buildup cap on a Theratron ⁶⁰Co therapy unit. Neutron shielding characteristics were measured by using an Am-Be source. The MCNP4C radiation transport computer code was used to investigate the effects of various shield thicknesses on the attenuation of gamma-ray photons and neutrons. Results: The concrete samples had a density of 4.0- 4.2 g/cm³. The compressive strength was 326 - 560 kg/cm². The calculated value for Half Value Layer (HVL) of the tourmaline-galena concrete samples for 60Co gamma rays was 2.72 cm, which is much less than that of ordinary concrete (6.0 cm). The MC-derived HVL for photons with the same energy was 2.77 cm, which is in a good agreement with the experimental data. Moreover, ToGa concrete had up to 10 times greater neutron attenuation compared to that of the reference concrete. Conclusion: Tourmalin-Galena Concrete opens a new horizon in economic and efficient gamma/neutron shielding in high-energy radiotherapy bunkers, nuclear power plants, and shielding of radioactive sources.