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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.

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–Molybdenum-alloy (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 Background Nasal septum deviation (NSD) can cause serious anatomical and clinical complications. It can change the breathing pattern and thus alter the anatomy of the airway structures. Despite its importance, the association between NSD with the nasopharynx volume (NPV) has not been assessed before. Therefore, we aimed to investigate it for the first time. Methods Archival CBCTs of 202 patients older than 17 years and without any history of trauma or pathology of the nasopharynx and without any orthodontic/orthognathic treatments were evaluated (129 women, 73 men, mean age: 36.24 ± 14.61 years). All included CBCTs must have been taken with a 12 × 8 field of view and fully covered the nasopharynx areas. The extent of NSD (°) and NPV (mm3) were measured. NSDs were categorized as mild (NSD ˂ 9°), moderate (9 ≤ NSD ≤ 15°), and severe (NSD ˃ 15°). Associations between sex, age, NSD, and nasopharynx volume were assessed using independent-samples t test, chi-square, one-way ANOVA, Tamhane post hoc test, Pearson and point-biserial correlation coefficients, and multiple linear regressions (α = 0.05). Results Mean NSDs were 11.27 ± 4.69° (range 1–19.5), 11.58 ± 4.63°, and 10.70 ± 4.76° in the sample, females, and males, respectively (P > 0.05). Of females, 27.9%, 40.3%, and 31.8% had mild, moderate, and severe NSDs. These were 35.6%, 39.7%, and 24.7% in males (P > 0.05). Mean NPVs were 4.88 ± 1.49, 4.80 ± 1.43, and 5.04 ± 1.60 mm3 in the sample, females, and males, respectively (P > 0.05). Mean NPVs were 6.41 ± 1.21, 4.87 ± 0.73, and 3.30 ± 0.65 mm3 in mild, moderate, and severe NSD groups (all P values = 0.000). Mean ages were 27.06 ± 6.49, 29.80 ± 9.64, and 54.73 ± 8.45 years in mild, moderate, and severe NSD groups (severe group being older than the other two groups, P = 0.000). NSD was strongly, negatively correlated with NPV (R = − 0.793, P = 0.000). Sex was not correlated with NPV or NSD (P ≥ 0.189). Age was negatively and positively correlated with NPV and NSD, respectively (P = 0.000). Modeling NSD (β = −0.776, P = 0.000) as a predictor for NPV rendered age effect insignificant (P > 0.05). Conclusions It was found, for the first time, that the more deviated the nasal septum, the smaller the nasopharynx volume. Aging might increase NSD and through it, reduce the nasopharynx volume. Sex might not affect NSD or NPV.

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.

Background: High-radiation therapeutic gain could be achieved by the modern technique of microbeam radiation treatment (MRT). The aim of this study was to investigate the dosimetric properties of MRT. Methods: The EGSnrc Monte Carlo (MC) code system was used to transport photons and electrons in MRT. The mono-energetic beams (1 cm × 1 cm array) of 50, 100, and 150 keV and the spectrum photon beam (European Synchrotron Radiation Facility [ESRF]) were modeled to transport through multislit collimators with the aperture's widths of 25 and 50 μm and the center-to-center (c-t-c) distance between two adjacent microbeams (MBs) of 200 μm. The calculated phase spaces at the upper surface of water phantom (1 cm × 1 cm) were implemented in DOSXYZnrc code to calculate the percentage depth dose (PDD), the dose profile curves (in depths of 0–1, 1–2, and 3–4 cm), and the peak-to-valley dose ratios (PVDRs). Results: The PDD, dose profile curves, and PVDRs were calculated for different effective parameters. The more flatness of lateral dose profile was obtained for the ESRF spectrum MB. With constant c-t-c distance, an increase in the MB size increased the peak and valley dose; simultaneously, the PVDR was larger for the 25 μm MB (33.5) compared to 50 μm MB (21.9) beam, due to the decreased scattering photons followed to the lower overlapping of the adjacent MBs. An increase in the depth decreased the PVDRs (i.e., 54.9 in depth of 0–1 cm). Conclusion: Our MC model of MRT successfully calculated the effect of dosimetric parameters including photon's energy, beam width, and depth to estimate the dose distribution.

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 CNEA-MEC 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.

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.

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 deep-seated 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. Immuno-fluorescent 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.

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 T1weighting 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 T1weighted sequence obtained with method 3. The minimum FI was −2.49%, which related to the minimal T1weighted 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, T1relaxation 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.

Background: Integrated proton therapy - MRI systems are capable of delivering high doses to the target tissues near sensitive organs and achieve better therapeutic results; however, the applied magnetic field for imaging, influences the protons path, changes the penetration depth and deflects the particles, laterally, leading to dose distribution variations. Objective: To determine the effects of a magnetic field on the range and the lateral deflection of protons, analytically. Methods: An analytical survey based on protons energy and range power law relation, without using small angle assumption was done. The penetration depth and lateral deflection of protons with therapeutic energy ranges 60- 250 MeV in the presence of uniform magnetic fields of 0-10T intensities, were calculated analytically. Calculations were done for relativistic conditions with Mathematica software version 7.0, and MATLAB 7.0 was applied to plot curves and curve fittings. Results: In the presence of a magnetic field, the depth of Bragg peak was decreased and it was shifted laterally. A second order polynomial model with power equation for its coefficients and a power model with quadratic polynomial coefficients predicted the maximum lateral deflection (ymax) and maximum penetration depth (zmax) variations with energy and magnetic field intensity, respectively. Conclusion: The applied correction for deflection angle will give more reliable results in initial energy of 250 MeV and 3T magnetic field intensity. For lower energies and magnetic field intensities the differences are negligible, clinically

Introduction: In radiotherapy, megaelectron volt (MeV) electrons are employed for treatment of superficial cancers. Magnetic fields can be used for deflection and deformation of the electron flow. A magnetic field is composed of non-uniform permanent magnets. The primary electrons are not mono-energetic and completely parallel. Calculation of electron beam deflection requires using complex mathematical methods. In this study, a device was made to apply a magnetic field to an electron beam and the path of electrons was simulated in the magnetic field using finite element method. Methods: A mini-applicator equipped with two neodymium permanent magnets was designed that enables tuning the distance between magnets. This device was placed in a standard applicator of Varian 2100 CD linear accelerator. The mini-applicator was simulated in CST Studio finite element software. Deflection angle and displacement of the electron beam was calculated after passing through the magnetic field. By determining a 2 to 5cm distance between two poles, various intensities of transverse magnetic field was created. The accelerator head was turned so that the deflected electrons became vertical to the water surface. To measure the displacement of the electron beam, EBT2 GafChromic films were employed. After being exposed, the films were scanned using HP G3010 reflection scanner and their optical density was extracted using programming in MATLAB environment. Displacement of the electron beam was compared with results of simulation after applying the magnetic field. Results: Simulation results of the magnetic field showed good agreement with measured values. Maximum deflection angle for a 12 MeV beam was 32.9° and minimum deflection for 15 MeV was 12.1°. Measurement with the film showed precision of simulation in predicting the amount of displacement in the electron beam. Conclusion: A magnetic mini-applicator was made and simulated using finite element method. Deflection angle and displacement of electron beam were calculated. With the method used in this study, a good prediction of the path of high-energy electrons was made before they entered the body.

Introduction: Since the heart of the electronic brachytherapy system is a tube of a miniature x-ray and due to the increasing use of electronic brachytherapy, there is an urgent need for acquiring knowledge about the X-ray spectrum produced, and distribution of x-ray dose. This study aimed to assess the optimal target thickness (TT), the X-ray source spectrum, and the absorbed dose of two miniature sources of hemispherical and hemispherical- conical used in electronic brachytherapy systems, through a Monte Carlo simulation. Methods: Considering the advantages of MCNPX Code (2.6.0), two input files corresponding to the characteristics of the investigated miniature sources were prepared for this code and then were used for simulation. The optimal thickness (OT) of gold and tungsten targets was determined for the energy levels of 40, 45, and 50 kilo-electron-volts. Results: In this study, the values of the size of the optimal thickness of 0.92, 1.01 and 1.06 μ for gold target and values of 0.99, 1.08 and 1.34 μ for tungsten target were obtained for energies 40, 45 and 50 keV that using these values, the optimum thickness of 0.92, X-ray spectrum within and outside targets, axial and radial doses for the used energy were calculated for two miniature sources. Conclusion: It was found that the energy of incident electron, target shape, cross-sectional area of the produced bremsstrahlung, atomic number of materials constituting of the target and output window are the factors with the greatest impacts on the produced X-ray spectrum and the absorbed dose

Introduction: Portable chest and abdomen x-rays are the most common x-ray procedures performed during hospitalization in the Neonatal Intensive Care Units (NICUs). These x-rays contribute to radiation exposure to several radiosensitive tissues, causing increased concerns about patients’ safety. This study aims to assess the status of radiological protection in the NICUs at two teaching hospitals supervised by Dezful University of Medical Sciences (DUMS), Dezful, Iran. Methods: A retrospective and observational study was performed at two teaching hospitals of DUMS comprising three NICUs. Six radiologic technology students were invited and agreed to participate in this audit. The students were asked to attend as observers in the NICUs and record the radiation safety principle observances specified in the checklist. We also supplemented data from an observational study with a retrospective survey of the images at the picture archiving and communication system (PACS) database. Results: 230 neonatal chest and abdomen x-rays from 65 hospitalized neonates were investigated during 57 work shifts in the observational survey. In all, 90.1%, 80% and 13% of the chest, abdomen and chest/abdomen x-rays had unsatisfactory beam restriction, respectively. The protective shielding tools were available; however, they were not commonly applied to the patients. Most of the personnel used fixed exposure parameters of 42 kVp and 3.2 mAs. In the retrospective study, 498 portable x-rays were retrieved from the PACS database, in which only 17.5% and 0.4% of images have adequate beam restriction and evidence of shielding, respectively. Conclusion: Our study is commensurate with previous literature and emphasizes that neonates in the investigated hospitals are receiving avoidable excessive radiation exposure, mainly due to inappropriate beam restriction.

Gonad shielding has been advocated to reduce radiation exposure in patients undergoing pelvic radiography. The aim of this study is to evaluate the frequency and accuracy of gonad shield placement in patients undergoing pelvic radiography. A retrospective study was performed on 1230 anteroposterior (AP) pelvic radiographs of 939 children under 16 years old. All the radiographs were reviewed to determine the frequency of gonad shielding and to evaluate whether gonad shields were correctly positioned when they are used. The gonad shield was present in 82 radiographs (30 girls and 52 boys) and was completely disregarded in 1148 radiographs. From 82 images which shield was present, the gonad shields adequately positioned in 28 radiographs (3 girls and 25 boys) and in the remaining 54 radiographs, the shield did not adequately protected the gonads due to incorrect placement of the shield. The inaccuracy placement and absence of gonad shields were more common in girls than boys (P-value < 0.05). More care should be taken to correctly positioning of the gonad shields in boys and its usage should be encouraged. However, the practice of ovarian shielding is not an effective way to reduce radiation exposure in girls undergoing pelvis radiography.