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Introduction: Irradiation of loaded tumor with high-Z nanoparticles with low energy photon of 192Ir source during brachytherapy increases absorbed dose of tumor due to increase in possibility of photoelectric phenomena. Therefore, this study aimed to investigate dose enhancement due to nanoparticles (NPs) with different atomic numbers and concentrations as well as effect of NPs distribution (uniform & non- uniform) on dose enhancement. Methods: Dosimetric parameters of HDR-192Ir source (MicroSelectron model) were calculated by MCNP-4C code on the basis of recommendations of AAPM, TG-43. A tumor (1 cm3) loaded with uniform and non-uniform distribution of 7, 18 and 30 mgr/gr of 79Au, 64Gd, 26Fe and 22Ti in water phantom (30×30×30 cm3) was simulated. Results: DEF of 4.7% to 19.4% and 3.3 to 18.6% were calculated respectively for uniform distribution of 79Au and 64Gd with 7 to 30 mgr/gr concentrations. For non-uniform distribution these values were 0.4%to 1.9% and 0.2% to 1.2%, respectively. Increased dose of the peripheral-health tissue due to presence of 2 to 8.5 mgr/gr of 79Au and 64Gd was estimated from 1.3% to 6.5% and 1.1% to 4.2%, respectively. Conclusion: increase of atomic number and concentrations of NPs enhance the absorbed dose due to increased possibility of photoelectric phenomena. Non-uniform distribution of NPs underestimated dose compared to uniform distribution therefore, considering accurate NPs distribution inside the tumor volume is crucial to calculation of dose enhancement. Targeted labeling of NPs for the maximum absorption by tumor and for the minimal penetration into peripheral tissues has potential to increase radiation therapeutic ratio.

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Introduction: ¹⁰³Pd is a low energy source, which is used in brachytherapy. According to the standards of American Association of Physicists in Medicine, dosimetric parameters determination of brachytherapy sources before the clinical application was considered significantly important. Therfore, the present study aimed to compare the dosimetric parameters of the target source using the water phantom and soft tissue.

Methods: According to the TG-43U1 protocol, the dosimetric parameters were compared around the ¹⁰³Pd source in regard with water phantom with the density of 0.998 gr/cm³ and the soft tissue with the density of 1.04 gr/cm³ on the longitudinal and transverse axes using the MCNP4C code and the relative differences were compared between the both conditions.

Results: The simulation results indicated that the dosimetric parameters depended on the radial dose function and the anisotropy function in the application of the water phantom instead of soft tissue up to a distance of 1.5 cm,  between which a good consistency was observed. With increasing the distance, the difference increased, so as within 6 cm from the source, this difference increased to 4%.

Conclusions: The results of  the soft tissue phantom compared with those of the water phantom indicated 4% relative difference at a distance of 6 cm from the source. Therefore, the results of the water phantom with a maximum error of 4% can be used in practical applications instead of soft tissue. Moreover, the amount of differences obtained in each distance regarding using the soft tissue phantom could be corrected.

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Introduction: The dosimetry of the brachytherapy sources is performed in the water source medium according to protocol TG-43U1. To achieve a resonable results on treatment, the use of the water material for all body tissues can be one of the faulty sources in delivering the correct dose to the tumor. Thus, we have focused on the dosimetry parameters in fat density 0.95 gr/cm³ and the muscle with density 1.05 gr/cm³ in the present study. The results are compared with the results of the water phantom to show the accurate accessment via the differences of the results.

Methods: Dissymmetry simulations for determining the parameters of the radial dose function and the anisotropy function in fat tissues, muscle and water phantom distances and different angles has been using MCNP4C code.

Results: The greatest relative differences of the phantom radial dose function of the fat tissue at distances below 1cm approximately reached 13%; and this rate increased, when the distance from the source increased; whereas at the distance of 5cm from the source, it approximately reached 167%. In the muscle tissue, the relative difference of these parameters was about 3% at the distance of 0.5cm, while at the distance of 5cm from the source, it approximately increased 16%. The maximum relative difference of the anisotropy parameter of the fat and muscle tissue phantom compared with the water were observed more than 2% and 3%, respectively.

Conclusion: In the clinical application of the ¹⁰³Pd brachytherapy source, which is contracted in the treatment of the adjacent malignant tumors to the fat and muscle tissues, the correct decisions must be applied on the tissue dosimetry parameters in the treatment planings according to the tables  of 3, 4, 5 and 6 in this study.

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Introduction: ^99mTc–Dimercaptosuccinic Acid (DMSA) as evaluation of pediatric genitourinary abnormalities has an important role in pediatric nuclear medicine. The aim of this study was to estimate organs absorbed dose for children injected by ^99mTc DMSA using MIRDOSE software and hybrid planar/SPECT method.

Methods: After injection of ^99mTc-DMSA, ten children with genitourinary abnormalities underwent 3-5 planar scans and single SPECT scan (at 1 to 20 h post injection). Also for anatomical reference of patients’ organs, MRI scans were performed for each patient. A hybrid planar/SPECT method was used to plot time activity curves for obtain source organs cumulated activity and then to calculate obserbed doses of organs MIRDOSE software was used.

Results: Mean absorbed dose due to ^99mTc-DMSA in pediatric for kidneys (200 ± 160), adrenals (15.1 ± 9.5), urinary bladder wall (14.7 ± 9.8), spleen (12.7 ± 7.8), gonads (12.4 ± 11.2), pancreas (10.5 ± 6.2), gall bladder wall (9.8 ± 5.7) , , , , , micro Sivert per MegaBequrel, respectively. Also, the mean effective doses was 10.01 ± 6.03 µSv/MBq.

Conclusion: The difference between the radiation doses received by the various organs of the patients caused by different amounts of radiopharmaceutical uptake in organs for different patients. Image quantities practical method using planar/SPECT hybrid method can be utilized with acceptable accuracy in determination of cumulative activity.

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Purpose: To study the benefits of Directional Bremsstrahlung Splitting (DBS) dose variance reduction technique in BEAMnrc Monte Carlo (MC) code for Oncor® linac at 6MV and 18MV energies.

Materials and Method: A MC model of Oncor® linac was built using BEAMnrc MC Code and verified by the measured data for 6MV and 18MV energies of various field sizes. Then Oncor® machine was modeled running DBS technique, and the efficiency of total fluence and spatial fluence for electron and photon, the efficiency of dose variance reduction of MC calculations for PDD on the central beam axis and lateral dose profile across the nominal field was measured and compared.

Result: With applying DBS technique, the total fluence of electron and photon increased in turn 626.8 (6MV) and 983.4 (6MV), and 285.6 (18MV) and 737.8 (18MV), the spatial fluence of electron and photon improved in turn 308.6±1.35% (6MV) and 480.38±0.43% (6MV), and 153±0.9% (18MV) and 462.6±0.27% (18MV). Moreover, by running DBS technique, the efficiency of dose variance reduction for PDD MC dose calculations before maximum dose point and after dose maximum point enhanced 187.8±0.68% (6MV) and 184.6±0.65% (6MV), 156±0.43% (18MV) and 153±0.37% (18MV), respectively, and the efficiency of MC calculations for lateral dose profile remarkably on the central beam axis and across the treatment field raised in turn 197±0.66% (6MV) and 214.6±0.73% (6MV), 175±0.36% (18MV) and 181.4±0.45% (18MV).

Conclusion: Applying dose variance reduction technique of DBS for modeling Oncor® linac with using BEAMnrc MC Code surprisingly improved the fluence of electron and photon, and it therefore enhanced the efficiency of dose variance reduction for MC calculations. As a result, running DBS in different kinds of MC simulation Codes might be beneficent in reducing the uncertainty of MC calculations. 

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Introdution: Intensity- modulated radiation therapy is one of the treatment methods for cancer tumors. The effectiveness of this method is dependent on the accuracy and treatment planning quality. Therefore, there is a need for a plan to select the angle and intensity simultaneous optimum of radiation.
Methods: In this study, an mixed integer linear programming model was proposed for simultaneous optimization of angles and intensity in the GAMS programming environment.To implement the model, after the patient's CT was prepared, the organ cantoring was performed by CERR software and the Influence Matrix was obtained for each organ. After collecting the inputs of the problem, in order to obtain the desired outputs, was used  from The GAMS software from the CPLEX solver.
Results: Finally, the actual case of head and neck cancer is analyzed to demonstrate the effectiveness of the model. From the angle of the candidate, ، is chosen as the optimal radiation angles. The maximum dose received by the brainstem was 3. 999, Mandible 70, LeftOrbit 0.026, RightOrbit 0.440, Parotid Gland 0.881, OpticChiasm 0.177, OpticNerves 0.167, spinalcord 9.929 Gray and the minimum dose received by the tumor is 70 Gray. Also, the optimal amount of intensity for implementing the treatment plan on the patient is achieved.
Conclusion: The dose received by each organ was significantly improved compared to prescribing doses. Similarly, the comparison of the Dose Volume Histogram obtained by solving a common problem with the model and software CERR, Represents the optimal performance of the model, which improves the security rate and reduces the cost for healthy tissues.

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Introdution: In advanced radiotherapy techniques such as intensity modulated radiation therapy (IMRT), the quality assurance (QA) is essential. This study aimed to compare the performance between Gafchromic^TM EBT3 film and Delta4^® phantom (2D and 3D) in heterogeneous chest phantom using IMRT technique.
Methods: In this experimental study, two IMRT plans (A and B) were prepared for radiotherapy of heterogeneous chest phantom. EBT3 film and Delta4 were used for dose measurement in the phantom. The 95% global gamma index accepted by the criteria of  3.3% mm and the dose threshold 20% as the standard criteria were considered in this study. The gamma index of the film and Delta4 were acquired by the verisoft and Delta4 software, respectively.
Results: The mean gamma index with standard criteria between treatment planning system (TPS) dose calculations and film measurements was 96.95%, while it was equal to 97.7% and 98.45% between TPS calculations and 2D and 3D Delta4 cases, respectively. The mean 3D gamma analysis of the Delta4 with the given standard criteria was 0.75% and 1.5% higher than their 2D gamma analysis of the Delta4 and film, respectively. The mean gamma index value of film and Delta4 according to the plan B at the standard criteria was 0.24% higher than plan A (97.7% vs 97.46%).
Conclusion: Both film and Delta4 showed acceptable standard gamma index for two plans implemented on the chest phantom using IMRT technique. So, according to the results of this study, it is concluded that in the centers where Delta4 is not available, EBT3 films with a simple heterogeneous phantom can be an alternative method.

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Introdution: The aim of this study was to evaluate and benchmark EGSnrc code in the simulation of 18 MV photon beam produced by Siemens Oncor® linear accelerator.
Methods: This study was conducted in a comparative and simulation based on experience method. The Beamnrc code was used to model the accelerator head and generate phase space files. The phase space files were obtained with the following parameters: field size of 10×10 , the energy of 14 Mev up to 14.8 Mev, and Full Width at Hall of Maximun of 0.12 cm. The phase space files were then used as input to the Dosexyznrc code to do dosimetry in the homogeneous water phantom with 50×50×50 size. Then, the output of DOSXYZnrc code, 3ddose files were used to obtain depth-dose curves and dose profile curves. Finally, Simulations were compared with experimental data by using gamma index.
Results: The energy tuning procedure have shown that the optimum energy and FWHM for the simulation model, were 14 Mev, 14.2 Mev , 14.4 Mev and 0.12 cm, respectively. The gamma index values, for depth-dose curves and dose-profile curve, were obtained less than 1.        
Conclusion: In this study, Monte Carlo model of Oncor® linac treatment head was simulated and the results have shown that the optimum nominal energy and FWHM were 14 Mev, 14.2 Mev, 14.4 Mev and 0.12 cm, respectively.

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Introduction: Bone scan is a nuclear medicine scan test, which leads to finding specific abnormalities in the bone. Methylene Diphosphonate (MDP) is used to bone scan. This combination is absorbed by bone tissue and is excreted by the kidneys and bladder. The purpose of this study was to estimate the absorbed dose of organs in bone scan with injection MDP radiopharmaceutical using Mirdose software and the SPECT/planar hybrid method.
Methods: 20 females who referred to the Nuclear Medicine Department for bone disorders were examined and three planar images intervals of 1, 3 and 5 hours and one SPECT at 3 hours after injection were taken from them. The cumulative activity of the organs was obtained using the SPECT/planar hybrid method and then the absorbed dose was calculated using Mirdose software.
Results: The mean absorbed dose due to ^99mTc-MDP in women for heart wall (0.0026±0.0005), kidneys (0.043± 0.0072), liver (0.0034±0.0001), lungs (0.0024±0.0001), muscle (0.0028±0.0006), ovaries (0.0056±0.0004), spleen (0.0048±0.0003), urinary bladder wall (0.0680±0.0120), bones (0.0046± 0.0006) and reminder of the body (0.0031± 0.00098) mGy/MBq were obtained.
Conclusion: Bladder, kidneys, ovaries, spleen, bones, liver, muscles, walls of the heart and lungs have the highest rates of absorbed dose in organs, respectively.Since the women studied in this study had different diseases and bone disorders and biological characteristics, and some of them were metastatic due to the disease, this led to a different absorption of radiopharmaceuticals in the various organs of these patients, which caused the difference is in the average absorbed dose of radiopharmaceuticals in their organs.
 

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Introdution: A careful study of the physical and biological properties of helium ion radiation on the various cell lines is essential for the treatment planning. In this study, the biological response of several different cell lines has been investigated in ⁴He ions.
Methods: Physical dose profiles and Linear Energy Transfer (LET) calculations were performed using the Monte Carlo Geant4 code. By studying the mixed radiation field, the biological effect of ⁴He primary ions, ³He and ⁶He secondary ions, as well as secondary proton, deuteron and triton are considered in calculations.
Results: Biological doses and cell survival levels have been compared for these cell lines. The variation of relative biological effectiveness (RBE) for each cell line is calculated as a function of the phantom depth. The results have shown that the cell lines with the highest (α/β)_ph levels have a higher sensitivity to damage cells against ⁴He radiation.
Conclusion: Among the studied cell lines, the most appropriate treatment for ⁴He ion, the Colon adenocarcinoma cancer cell line has been selected. In addition, due to the large variation in RBE relative to the depth in the phantom, it is necessary to consider a variable RBE instead of a constant RBE.

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Introdution: Today, the Advantages of radiation therapy by charged particles is indicated for the treatment of cancerous. During the passing of proton beam in the body tissues, secondary particles produce, which penetrate to the body healthy tissues and cause damage. The aim of this research was calculating the Spread out Bragg Peak for covering the breast cancer and investigating arrived dose to the different parts of the heart during the treatment process.
Methods: In this simulation study, a spherical tumor with a diameter of 1 cm considered in right breast tissue in MIRD phantom and then irradiated by proton of right and front sides of the body. Simulations are performed using the MCNPX code.
Results: The Spread out Brag Peak calculated to cover the breast cancer in two cases of radiation. In the radiation of front and right, the deposited Dose due to The Proton Particle in tumor are 4.25 nGy and 4.12 nGy, respectively. The dose due to the protons and secondary particles in different parts of the heart calculated and compared for two modes of radiation. Energy Ranges of neutrons was about 55 MeV and for electrons and photons was less than 20 MeV. Although, the dose due to the secondary particles was very low in comparison of protons dose.
Conclusion: In proton therapy, a large portion of the dose is evacuated in the tumor. Proton radiation of the front in comparison of the right leads to the more dose deposit in the tumor and heart.

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Introduction:In PET imaging, one or both of two annihilation photons may change the direction before reaching the detector due to Compton scattering interaction in body.
.Methods:This article, a Monte Carlo simulation study, examined the effect of soft tissue on this error.In this work, the PET Biograph^TM 6 scanner, a simple geometry of soft tissue -including a sphere of soft tissue in center of PET ringwith various radii (from 0.5 to 30cm)- and two kinds of 511keV gamma source –point source and spherical source - were simulated by Monte Carlo MCNPX code to investigate scattering effect of soft tissue on PET imaging.
Results:Analysis of the results of the simulation showed that, the majority scattered photons fell within the energy window without much loss of energy. Soft tissue around the point source at a distance of 8 to 12cm from the source and soft tissue around the spherical source at a distance of 8cm from the center had the most scattering effect in PET imaging. The scattering effect of soft tissue around the point source was more than the spherical source.
Conclusion:The scattering effect of the adjacent organs is more than the non-adjacent organs.For high thicknessof soft tissue (more than20cm of radius), the attenuation effect is as obvious as the scattering effect. According to the results of this study, the patient's body thickness -in the abdominal region-could be a more accurate alternative for the patient's weight for increasing the injected dose into obese patients.

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Introduction: Recently, the use of various sensitizers has been used to increase photon-induced doses in brachytherapy. One of these cases is the addition of heavy metal nanoparticles such as gold in the target area, which increases the production of ionizing electrons by increasing the possibility of photoelectric effects, and increases the efficacy of the treatment. In this study, the target of the irradiation was the endothelial cell in the wall of blood capillaries located inside the tumor, which, if destroyed, would result in abnormal blood cell counts and tumor cell death.
Methods: The effect of using nanoparticles of gold, silver, bismuth and copper has been evaluated by calculating the dose increase ratio using Geant4 tool that was based on Monte Carlo method. These calculations were performed on two microscopic (cellular) and macroscopic (tumor dimensions) scale and the effects of different concentrations of these nanoparticles were compared. Also, the dose increase ratio has been evaluated to determine the most appropriate photon energy range.
Results: As the concentration of nanoparticles increases, the dose enhancement factor increased in photon energy. In addition, for energies less than 70 keV, with increasing energy, dose enhancement factor increased and for energies above 80 keV, this quantity decreased with increasing energy.
Conclusion: In terms of dose, gold is the best option, and in terms of the dose enhancement factor, silver and bismuth are better alternative among the four elements studied. Also, the most suitable photon energy range is 70 keV to 80 keV.
 

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Introduction: Today electrophysiology studies and ablation have been developed due to increasing arrhythmias disorder of heart. In these diagnostic – treatments methods, the use of fluoroscopy can be causes patient radiation dose, therefore evaluation of patient's absorbed dose is necessary to protection of the radiation. The aim of this study was to evaluate the absorbed dose in patients undergoing electrophysiology and cardiac ablation and to estimate their risk of cancer in Yazd Afshar Hospital.
Methods: This study was a cross-sectional study. In this study, the mean absorbed dose of referral patients for electrophysiology studies and ablation had been measured in the cat. Lab of Afshar Hospital, Yazd. The dosimeter had been used in this research was KAP meter, the M4 DIAMENTOR made in Germany that was able to measure dose-area product and time of the fluoroscopy. The patient effective dose was calculated by the PCXMC software from dose-area product.
Results: The mean dose-area in ablation and electrophysiology studies was respectively 153.34±105.32 and 5.62 14.88 Gy.cm² and the radiation time range was recorded 3.32 to 68.65 minutes and 1.03 to 6.28 minutes, respectively. The mean effective dose of ablation and electrophysiology studies were respectively 16.38 and 1.65 mSv. The cancer risk per ten thousands of patients, who were under the ablation and electrophysiology examinations were estimated 13 and 1.3 people, respectively.
Conclusion: Increasing of patient dose due to ablation in this study relation to the other studies can be due to long old of image intensifier device.
 

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Introduction: Nowadays the use of cone beam computed tomography in dental imaging is increasing, although this method has a much lower dose than conventional CT scans, it delivers a higher dose than the panoramic and periapical patients therefore, , the aim of this study was to investigate the factors affecting the patients' dose in dental CBCTs and methods of optimizing and reducing the patients' dose.
Various factors such as the use of thyroid collar, lead goggles, field size, device type, imaging parameters such as tube voltage and current, alternating or pulsed radiation; type, amount and shape of the filter, 360 degree or partial rotation of tube and scan time, can affect the absorbed dose of the patient in dental CT scans. Among these, the use of thyroid collar (42% reduction), lead goggles (6% reduction),the smallest possible field of view ( up to 90%), pulse irradiation, patient sitting position and 180^o rotation angle instead of 360^o (more than 50% reduction) cause significant reduction in the organ doses and effective dose of the patients. It should also be kept in mind that measures taken to reduce the patients' dose should not impair image quality and, depending on the patient's condition, the radiographer will select the dose reduction parameters without degrading the image quality.

 

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