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Purpose: The presence of a dental implant across the irradiation beam has the potential to perturb the dose distribution. In this study, the effect of different commercial dental implants on dose distribution was investigated in electron beam therapy. Materials and Methods: The Varian 2100 C/D linear accelerator (Linac) head was modeled precisely with proper components for electron mode (6 and 9 MeV) by MCNPX 2.6.1 and was benchmarked according to the International Atomic Energy Agency (IAEA) protocol, TRS -398. Dose distribution was calculated for Six different implant materials, including Titanium, Titanium alloy, Zirconia (Y-TZP), Zirconium oxide, Alumina, and PolyetherEtherKetone (PEEK), and for Four different scenarios. Results: The highest and lowest increasing doses occurred for Y-TZP (114.44% and 108.69% for 6 and 9 MeV, respectively) and PEEK (104.85% and 98.84% for 6 and 9 MeV, respectively) directly in front of the implant, respectively. By removing an implant from the jaw, an increasing dose was not seen, but an increasing dose occurred behind its depths in the bone region (31.81 %). Conclusion: The amount of dose perturbation due to the dental implant's presence depends on the beam energy, mass density, and atomic numbers of implants. Maximum and minimum increased doses were estimated for Y-TZP and PEEK implants, respectively. Considering the correction factors due to the presence of high density and atomic number dental implants are essential to estimate the accurate dose delivery in radiotherapy with electron beams. [ABSTRACT FROM AUTHOR]

Purpose: The impact of various hip prosthesis materials on the amount of dose perturbation generated by 9 MeV electron and 18 MV photon beams during pelvic radiation therapy is analyzed in this research. Materials and Methods: The Varian 2100 C/D LINAC head for the electron (9 MeV) and photon (18 MV) modes and a water phantom with a realistic hip prosthesis were modeled using the Monte Carlo (MC) code; MCNPX (Ver. 2.6.0) and were benchmarked for measurement. Four different materials, including Cobalt-Chromium-Molybdenumalloy (CCM), Stainless Steel (SS), Titanium, and Titanium-alloy (Ti-alloy) were evaluated. The changes in electron and photon fluences and dose perturbations due to the presence of the hip prostheses were investigated. Results: An increased dose of 13.29%, 13.77%, 6.16%, and 5.93% for 9 MeV and 30.43%, 33.05%, 10.89%, and 11.27% for 18 MV was calculated for Ti-alloy, Ti, CCM, and SS prosthesis, respectively. At 0.5 mm distance from the prosthesis, the Electron Backscatter Factor (EBF) of 1.31, 1.33, 1.15, and 1.14 for 9 MeV and 1.32, 1.34, 1.11, and 1.12 for 18 MV was calculated for Ti-alloy, Ti, CCM, and SS prosthesis, respectively. Dose perturbation is higher at a near distance from the prosthesis; by reducing the distance from the Ti-alloy prosthesis (1.5 to 0.5 mm), an increased dose of 7.70% and 5.54% resulted in 18 MV and 9 MeV, respectively. The dose decreases of up to 21% behind the hip prosthesis were calculated for 18 MV. Conclusion: It is essential to consider the dose perturbation due to the presence of a hip prosthesis to achieve the optimal treatment planning in radiotherapy. [ABSTRACT FROM AUTHOR]

Background: It is recommended for each set of radiation data and algorithm that subtle deliberation is done regarding dose calculation accuracy. Knowing the errors in dose calculation for each treatment plan will result in an accurate estimate of the actual dose achieved by the tumor. Objective: This study aims to evaluate the equivalent path length (EPL) and equivalent tissue air ratio (ETAR) algorithms in radiation dose calculation. Material and Methods: In this experimental study, the TEC-DOC 1583 guideline was used. Measurements and calculations were obtained for each algorithm at specific points in thorax CIRS phantom for 6 and 18 MVs and results were compared. Results: In the EPL, calculations were in agreement with measurements for 27 points and differences between them ranged from 0.1% to 10.4% at 6 MV. The calculations were in agreement with measurements for 21 points and differences between them ranged from 0.4% to 13% at 18 MV. In ETAR, calculations were also in consistent with measurements for 21 points, and differences between them ranged from 0.1% to 9% at 6 MV. Moreover, for 18 MV, the calculations were in agreement with measurements for 17 points and differences between them ranged from 0% to 11%. Conclusion: For the EPL algorithm, more dose points were in consistent with acceptance criteria. The errors in the ETAR were 1% to 2% less than the EPL. The greatest calculation error occurs in low-density lung tissue with inhomogeneities or in high-density bone. Errors were larger in shallow depths. The error in higher energy was more than low energy beam. [ABSTRACT FROM AUTHOR]

Introduction: It is well known that neutrons are more effective treatments than photons to treat hypoxic tumors due to the interaction with the nucleus and the production of heavy particles. This study aimed to evaluate the suitability of Boron neutron capture therapy (BNCT) for the treatment of lung cancer. To this end, neutron dose distributions were calculated in lung tumor volume and peripheral organs at risk (OARs). Material and Methods: Dose distribution to treat lung cancer was calculated by MCNPX code. An elliptical tumor with a volume of 27cm3 was centered in the left lung of the ORNL phantom and was irradiated with neutron spectrums of Massachusetts Institute of Technology (MIT) and CNEA-MEC. The tumor was loaded with different concentrations of Boron 0, 10, 30, and 60 ppm to evaluate the delivered dose to OARs. Results: Neutron absorbed dose rates in the tumor were 2.2×10-3, 2.6×10-3, 3.4×10-3, and 4.7×10-3 Gy/s for boron concentrations of 0, 10, 30, and 60 ppm, respectively for MIT. Moreover, similar results for CNEAMEC were 1.2×10-3, 1.6×10-3, 2.5×10-3, and 3.7×10-3 Gy/s. The heart absorbed the maximum neutron dose rate of 1.7×10-4 and 1.6×10-4 Gy/s in MIT and CNEA, respectively. For all energy bins of spectrums, the neutrons flux is decreased as it penetrates the lung. Conclusion: An increase in boron concentrations in tumors increases the absorbed doses while deteriorates dose uniformity. The results show that the MIT source is well suited to treat deep lung tumors while maintaining the OARs' dose within the threshold dose. [ABSTRACT FROM AUTHOR]

Introduction: Physical wedge by modify photon beam shape and intensity has been utilized in radiotherapy to obtain uniformly dose distribution in tumor site with reduced hot spots. Calculation of dosimetric parameters for both symmetric and asymmetric wedged fields is proved necessary during linear accelerator (Linac) commissioning. The present study aimed to achieve output factors and dose profiles for symmetric and asymmetric wedged fields of 6 MV beams. Material and Methods: The Siemens PRIMUS Linac head for 6 MV beam was simulated by BEAMnrc and all dose calculations were performed by DOSXYZnrc code. Percentage depth dose (PDD) and profiles for open and wedged (15° and 45°) fields were compared with corresponding measurements. Wedge factors for 10 x 10 cm² field were obtained as a function of lateral distance as well for half beam wedged fields. Results: Based on the results of the present study, the calculated doses were in agreement with the measured data. The output factors on the central axis of symmetric wedged beams decreased to 0.693 and 0.307 for 15°, and 45° wedges. The total photon fluence of 15° and 45° physical wedged fields reduced to 71.6% and 27.7% of open field, respectively. Conclusion: The output factor for asymmetric wedged fields was found to be lower than corresponding symmetric open and wedged fields, particularly at field edges. Lack of scattering photons near the half beam edges resulted in dose fall-off in these regions possible to be overestimated by treatment planning system and consequently caused cold spots at target volume. [ABSTRACT FROM AUTHOR]

Background: Considering the non-invasive nature of magnetic resonance spectroscopy (MRS) and its ability to detect prostate lesions, the present study aimed to investigate the accuracy of MRS techniques in distinguishing between prostate cancer (PCa) and prostatitis. Methods: Thirty-three patients (18 patients with PCa and 15 patients with prostatitis) were recruited for this study. Magnetic resonance imaging (MRI) and MRS were performed using 1.5-T system GE- modle Optima 450 Discovery (GE Medical Systems, US). The (Cho+Cr)/Cit ratio of hypointense T2 areas were calculated. The diagnostic accuracy including sensitivity and specificity indices, with 0.95 confidence interval as well as PPV and NPV were calculated for each variable. The receiver operating characteristic (ROC) area under the curve (AUC) was outlined and investigated. The mean quantitative values between the two groups (PCa and Prostatitis) were compared using independent t test. Results: The mean ratios of Cho+Cr/Cit in PCa was 1.54 ± 0.63 and 0.83 ± 0.48 for PCa and prostatitis, respectively, indicating a significant statistical difference (P = 0.00). A reduction in citrate was seen in both PCa and prostatitis tissue. Significant elevation in choline peak was shown for PCa. Moreover, creatinine level was low in both normal tissue and PCa without significant difference. Sensitivity, specificity, accuracy, PPV and NPV of MRS were 94.4% (95% CI, 74.2--99), 80% (95% CI, 54.8--93), 96%, 85% and 92.4%, respectively. Conclusion: The results of this study indicate an acceptable level of sensitivity, specificity and accuracy of MRS in the differential diagnosis of PCa and prostatitis. [ABSTRACT FROM AUTHOR]

Aims and Objectives: Brachytherapy using removable ophthalmic plaques loaded with suitable small sealed radioactive seeds adjacent to the ocular's tumor has been widely used as an effective treatment. The aim of this study was to investigate the dose distribution in a modeled eyeball followed to loading of an ocular melanoma tumor with different concentrations of gold nanoparticles (GNPs) as dose enhancement agent by Monte Carlo (MC) calculations.Materials and Methods: The MC code of MCNPX 2.6.0 was used to modeling of COMS standard eye plaque loaded with 24 125I sources (6711 model) located on the sclera of modeled eyeball with detailed structures and materials. A choroidal melanoma tumor was simulated and loaded with different concentrations of spherical gold GNPs (50 nm in diameter). Dose enhancement factors (DEFs) of ocular components were calculated.Results: The dosimetric properties of 125I source (6711 model) and dose distribution of COMS standard eye plaque were calculated successfully as recommended by TG-43U1; AAPM. Loading of tumor with GNPs increased dose to the tumor and decreased dose to the normal tissues; the DEF was increased up to 2.280 and 2.030 for tumor apex, while it was decreased to 0.760 and 0.892 for macula and for gold-tumor mixture and nanolattice distributions, respectively.Conclusion: Loading the choroidal tumor volume with GNPs improves the dose distribution by increasing dose to the tumor and decreasing dose to the health components in ocular brachytherapy with 125I seeds 20-mm COMS plaque. [ABSTRACT FROM AUTHOR]

Background: Noninvasive quantification of liver fat by gradient echo (GRE) technique is an interesting issue in quantitative magnetic resonance imaging. In this study, the fat content in patients with nonalcoholic fatty liver disease (NAFLD) was quantified with GRE sequences with different T1 and T2* weighting. Methods: This prospective, cross-sectional study was performed on thirty NAFLD patients. Sixteen GRE sequences with different T1 weighting were performed with four echo times. In each sequence, repetition time (TR) or flip angle was changed and other parameters were fixed. Forty-eight fat indexes (FIs) from 16 sequences were calculated based on three methods. To determine the relationship between FIs and histological findings, Pearson's correlation coefficient was used at the level of 1% significance. Results: Mean FIs which obtained from Eq. 3 have the maximum values in comparison to other FIs. The maximum FI was 23.58%, which related to heavily T1 weighted sequence obtained with method 3. The minimum FI was -2.49%, which related to the minimal T1 weighted obtained with method 2. FIs increase with a flip angle, especially at low flip angles. Increase the TR parameter decrease the FIs gradually. Calculated FIs with methods 1 and 3 stronger correlated with histological findings relative to calculated FIs with method 2. Conclusion: For fat quantification, T1 relaxation effects probably more critical than T2*. Flip angle parameter could be a major factor causing the overestimation of liver fat content. Sequences with low flip angle are more suitable for fat quantification with methods 1 and 3. In fat quantification with GRE techniques, it is possible that the third and fourth echoes are unnecessary. [ABSTRACT FROM AUTHOR]

Objective(s): Taking advantage of high atomic number of gold nanoparticles (GNPs) in radiation dose absorbing, many in vitro and in vivo studies have been carried out on using them as radio-sensitizer. In spite of noticeable dose enhancement by GNPs at keV energies, using this energy range for radiotherapy of deepseated tumors is outdated. The aim of the present work was to examine the effect of GNPs on radio-sensitivity of HT-29 cells in combination with 18 MV X-rays. Materials and Methods: GNPs were synthesized using a seed-growth method and characterized by transmission electron microscopy (TEM) for size and morphology. Cytotoxicity effect of the GNPs as well as amount of uptake into the HT-29 cell line was assessed. Irradiation was done by 18 MV photons. Immunofluorescent imaging of γ-H2AX foci and clonogenic assay were conducted to find out the effect of the GNPs on radio-sensitivity of the cells. Results: The size of GNPs was about 24 nm with a spherical-like shape. Treatment of the cells with the GNPs induced insignificant inhibition in cell growth. Cellular uptake reaches a maximum after 12 h incubation with GNPs. Stained γ-H2AX foci showed a significant difference in number and intensity for GNPs treated cells compared to only irradiated one. Moreover, colony formation assay proved an impressive decrease in the number of colonies for the irradiated+GNPs group rather than the other one. By fitting the survival fraction data on the linear-quadratic model, sensitization enhancement factor (SER) of 1.25 was achieved. Conclusion: Although theoretical studies predicted negligible radio-enhancement factor for GNPs at high megavoltage energies, present results show the potential of GNPs for possible gold nanoparticle-aided radiation therapy (GNRT) even for high MV photons. [ABSTRACT FROM AUTHOR]

In recent years, the use of gold nanoparticles in radiation therapy has been introduced as a new approach in radiotherapy. The aim of this study is to investigate the effect of gold nanoparticles (GNPs) in plaque brachytherapy for choroidal melanoma using Monte Carlo (MC) simulation. MCNPX code was used for simulation of human eye, Pd (model 200) brachytherapy source and the 20 mm COMS eye plaque that was loaded with 24 Pd seeds and standardized by Collaborative Ocular Melanoma Study (COMS). The tumour was defined from the inner surface of choroid with 0.55 cm height and latticed with gold nanospheres and it was filled with different concentrations of 5, 10 and 15 mg/g GNPs, separately. Dose rate and dose enhancement factor in tumour and normal tissues of the eye (without gold) was examined for this case and compared with gold-water mixture of the same concentrations distributed in the tumour. The results show that with increasing the concentration of GNPs, the dose in the tumour increases and the dose to the normal tissues decreases. Furthermore, the time that is required to deliver the prescribed dose to the tumour decreases. In the gold nanosphere case for 5, 10 and 15 mg/g concentrations, the DEF in the apex of the tumour are 1.28, 1.46, 1.44 and at the distance of 6.5 mm in the normal tissue (outside the tumour) this factor would be 0.82, 0.73 and 0.68. The comparison between two cases of gold nanospheres and gold-water mixture shows that when the gold concentrations are defined as mixed with water, the dose enhancement in the first depths are higher than when the gold-nanoparticles are distributed inside the tumour. Furthermore due to more reduced particle flux for water-mixture case, by an increase in the depth the dose enhancement in gold-nanosphere increases compared with gold-water mixture case. [ABSTRACT FROM AUTHOR]

Background: Gonad shielding has been extensively advocated during pelvic radiography at or below reproductive ages. The popular practice of gonad shielding is placement of a lead shield in the midline of the pelvis. The aim of this study was to address the prevalence of gonad shielding and find out whether the current practice of gonad shielding can be considered as an effective method to reduce radiation exposure in patients undergoing pelvic radiography. Methods: National and international electronic databases, including PubMed, MEDLIN, EMBASE, and Google-Scholar, were searched up to January 2016. The database searches were supplemented with manual searches of reference lists. Two authors independently assessed the eligibility of all studies and extracted data. Results: The searches yielded a total of 243 publications. After assessing each identified study against specific inclusion exclusion criteria, 18 studies were deemed as relevant for this review. The total prevalence rate of gonad shielding was estimated at 58% (95% CI: 40 to 74%). It was estimated that only 34% (95% CI: 25 to 44%) of the radiographs had correct positioning of the shield. Also, incorrect positioning of the shield was statistically significantly higher in females than males (85% vs. 52 %; P-value <0.001 ). Conclusions: Our study demonstrates that the current practice of gonad shielding during female pelvic radiography should be no longer considered as an effective method to reduce radiation exposure. Training the best qualified radiographers is the key to accurate positioning of the shield in male subjects. [ABSTRACT FROM AUTHOR]

Background: Fetography has named the radiography of the fetus in utero. Due to the potential risk of radiation-induced cancers and other malignant effects, this procedure has avoided and has completely replaced by ultrasonography. However it has observed that this invasive procedure has still followed in some clinical departments. Objectives: The aim of this study was to assess the current status of the fetography and its prevalence as an un-recommended diagnostic procedure in teaching hospitals of Ahvaz, Iran. Methods: The radiology and ultrasonography reception systems of two teaching hospitals of Ahvaz have investigated to identify pregnant patients who has undergone fetal presentation imaging (cephalic or breech) between 21 March 2013 and 21 March 2015. Results: In general 3741 pregnant women who have undergone fetal-presentation imaging during two past years have identified. There was significant statistically differences between X-ray and ultrasonography examinations (2528 vs. 1213; P value < 0.05), as those have accounted for 67.5% and 32.5% of the performed examinations, respectively. Women younger than 30 years, who were more sensitive to radiation, accounted for 51.2% of the X-ray examinations. The number of fetographies has increased as much as 2.2 fold during 2013 to 2015. Discussion: Women of the investigated hospital have received avoidable fetal irradiation due to fetography then it was a reason for concern. Ultrasonography should be the first-line imaging modality for pregnant women, especially in the case of fetal presentation. [ABSTRACT FROM AUTHOR]

Aims and Objectives: The present study aims to evaluate and compare the dose enhancement factor (DEF) of tumor injected with different nanoparticles (NPs) around high dose rate (HDR) (192)Ir brachytherapy source.Materials and Methods: Monte Carlo calculations were performed with MCNPX code to determine the DEF caused by in tumor injected with (79)Au, (64)Gd, (26)Fe, and (22)Ti NPs during HDR (192)Ir brachytherapy. The uniform and non-uniform distribution of NPs within tumor was modeled with simple NPs-water mixture, and realistic nano-scale-lattice model. Furthermore, a margin of (79)Au and 64 Gd NPs was implemented around the tumor volume.Results: The increased dose caused by uniformly distributed (79)Au and 64)Gd NPs with 7, 18, and 30 mgr/gr concentrations was 4.7%, 11.8%, 19.4%, and 3.3%, 8.3%, and 18.6%, respectively. For non-uniform distribution, it was 0.4%, 1.2%, 1.9%, and 0.2%, 0.7%, and 1.2%, respectively. Increased tumor dose due to (26)Fe and 22 Ti was not significant. The peripheral-healthy tissue dose as margin with 2, 5, and 8.5 mgr/gr of 7(9)Au and 6(4)Gd increased by 1.3%, 3.6%, 6.5%, and 1.1%, 2.5%, and 4.2%, respectively. Increase the radial depth of tumor (from 1.5 to 5 cm) increase DEF (up to 22.3%). The nano-lattice model underestimated the DEF up to 4% and 3.6% for 79Au and (64)Gd NPs, respectively.Conclusion: Injecting of high-Z gold NPs into tumor increases the absorbed dose of tumor irradiated with (192)Ir HDR brachytherapy source. Size, geometry, concentration, and distribution model of NPs and tumor depth are crucial factors to accurately estimate the DEF. [ABSTRACT FROM AUTHOR]