Introduction: Patient dose is the most important concern for any new X-ray system. The dose received by the patients depends on the imaging technique, the optimization of the collimator, filtration and field of view (FOV). The purpose of this study is to evaluate the effect of various imaging parameters on dose received by different organs in a dental CBCT scanners. Material and Method: In this study, dental CBCT system (Planmeca 3d mid) including the X-ray tube, flat panel detector and a voxelized phantom, was simulated by the GATE Monte-Carlo Code (Version 8). DICOM CBCT images of a person, and Alderson Rando phantom were segmented using MATLAB and 3D slicer software to identify various organs such as bone, bone marrow, soft tissue, brain and thyroid. Results: The half value layer of the simulated X-ray was found to be 2. 6 mm which differed from the experimental value by approximately 6. 47%. In some cases, the 3D dose distribution for Rando Phantom was less than that for Voxelized phantom simulated by CT images of a normal person. Conclusion: The reason of this difference is attributed to the different substances definition. The difference in experimental and simulation data can be due to several reasons i. e. the inaccuracy caused by the use of a limited number of TLDs in experimental measurements, the impossibility of simulating Gentry's actual rotation (hyperbolic's rotation) and the uncertainties caused by converting CT images to e Voxelized phantom.

Background: Exposure conditions in CT examinations are quite different from conventional X-ray. In CT examination higher dose is given to patient in comparison with the dose in other diagnostic examinations. In order to calculate organ effective dose in chest CT, Monte Carlo simulation has been used in this study. Materials and Methods: The Impact survey data were used to determine the parameters related to patient dose. This was done by correlating the measurements from the NRPB scanners with the effective dose calculated, using the CTDOSE software. Patient dose index in air (CTDIair) was measured as function of tube exposure ranged from 90 to 225mAs at constant kVp and slice thickness, using a stack of TLD chips which as long enough to fully encompass the dose profile that could have been used. Results: Dose profile of each exposure was measured with approximately Gaussian distribution shape. The full width at half maximum (FWHM) of these profiles was nearly equal, and on average it was equal to 8 cm. Also the maximum CTDIair for these profiles, as expected increased with mAs ranging from 29.2 to 50.606 mGy.  TDIair was measured by two methods using conversion coefficient established by using software, based on Monte Carlo simulations (CTDOSE) and the other was measured in the area under the dose profile distribution. Conclusion: The slice thickness measured from FWHM and those thicknesses set by the operator were nearly equal proving that the measurements using TLD were accurate. The effective dose for chest increased with increasing mAs. By these measurements, it was also noted that the maximum equivalent dose and sharpest slope variation were for lungs, heart and breast respectively, whereas the minimum equivalent dose with lowest slope variation was related to thyroid, liver, spleen, stomach wall and kidneys respectively.

Background: The same conversion factors (k-factors) of Single CT (SECT) are applied to estimate the Effective Dose (ED) in Dual Energy Computed Tomography (DECT). However, k-factors for different organs need independently validating for DECT, due to the different conditions in DECT. Objective: This study aimed to calculate organ dose and k-factors in different imaging protocols (liver, chest, cardiac, and abdomen) for male and female phantoms. Material and Methods: This Monte Carlo Simulation study used Monte Carlo N-Particle (MCNP) code for modeling a Siemens Somatom Definition Flash dualsource CT scanner. The organ dose, dose length product, and k-factors were calculated for the Medical Internal Radiation Dose (MIRD) of male and female phantoms. Results: For the male phantom, the k-factors for the liver, chest, cardiac, and abdomen-pelvis imaging protocols are equal to 0. 020, 0. 012, 0. 016, and 0. 014 mSv. mGy−, 1cm−, 1, respectively. For the female phantom, the corresponding values are equal to 0. 026, 0. 023, 0. 036, and 0. 018, respectively. These values for DECT are different from those corresponding values for SECT, especially for the female phantom. Conclusion: The calculated k-factors for DECT can be used as reference values for the estimation of ED in DECT.

Introduction: Organ dose estimation using thermoluminescence dosimeter (TLD) is known to be a standard, although many other methods, such as simulation software, optically stimulated luminescent dosimeters, and photodiodes are still in use. This study aimed at directly measuring mean organ doses to the selected organs in the head/neck, chest, and abdominal regions from four computed tomography (CT) units in Lagos, south-west of Nigeria. Material and Methods: This study was conducted on locally constructed inhomogeneous phantoms to measure mean organ doses to the head/neck, chest, and abdominopelvic regions from CT units in the Lagos metropolis, Nigeria. Lithium fluoride doped with magnesium and titanium (LiF: Mg, Ti) TLD was used for the measurement. Statistical analysis was performed by IBM SPSS (version 20). Results: Validation of the designed phantoms was below ± 20% kVp and mAs parameters among the CT units, which was statistically different with regard to the observed dose discrepancies. Generally, a one-way ANOVA showed that there was a statistically significant difference in the investigated mean organ dose (P = 0. 043). The comparison of the obtained results from this study with those of other studies revealed that there was no statistically significant difference in the TLDs (P > 0. 05). The maximum relative difference in the dose was < 200%. Conclusion: The designed phantoms seemed to be useful for CT dose validation and could be used to validate simulation software in areas where readymade phantoms are not available.

Background: The computed tomography (CT) scan delivers a relatively high radiation dose to the patient. One of the critical factors that affects the absorbed dose is the intensity of tube current. The aim of this study is to measure and compare the radiation dose of three radiation-sensitive organs in constant current mode and tube current modulation (TCM) modes. Materials and Methods: CT-scans from the chest and abdomen-pelvis regions of adults in three different current modes were obtained. The absorbed doses of thyroid, lungs, and ovaries were measured using the thermoluminescent dosimeter (TLD) chips embedded in the RANDO phantom. Furthermore, the confirmation of the organ doses was simulated using the Monte Carlo (MC) simulation. The measured doses were evaluated and confirmed by comparison with the simulated doses. Results: The relative differences between the measured and simulated doses for thyroid, lung, and ovary were-4. 7%,-1. 3%, and-11. 7% for constant current mode,-2. 2%,-11. 2%, and-6. 3% for longitudinal modulation mode, and 0. 0%,-14. 6%, and-9. 9% for angular modulation mode, respectively. With longitudinal modulation mode, thyroid, lung, and ovary doses were reduced by 34. 0%, 19. 0%, and 19. 0% for the measured doses and 32. 0%, 26. 0%, and 13. 0% for the simulated doses, respectively. The longitudinal modulation mode resulted in a greater dose reduction compared to the angular modulation for both measured and simulated doses. Conclusion: Using TCM resulted in reducing does received by the organs in both measured and simulated doses. The TCM reduces organ dose, which is more evident in the longitudinal modulation.

Background: This study sought to assess the organ absorbed dose using ImPACT software and evaluate the effect of small and large fields of view (FOVs) for three cone-beam computed tomography (CBCT) devices on the organ absorbed dose. Materials and Methods: The weighted computed tomography dose index (CTDIw) is measured using a pencil ionization chamber which was incorporated in a polymethyl methacrylate (PMMA) phantom for three CBCT devices with small and large FOVs. The calculated CTDIw was entered into the ImPACT software. Then the organ absorbed dose of the thyroid gland, salivary glands, oral mucosa, skin, brain, and red bone marrow and the whole-body effective dose were calculated by the software. Results: Irrespective of the type of CBCT device, the organ absorbed dose was obtained higher value in use of a larger FOV (P<0. 01). The mean organ absorbed dose in use of large and small FOVs was 0. 13 and 0. 08 for New Tom GiANO, 0. 49 and 0. 13 for Vista Vox S and 0. 69 and 0. 38 for XMIND Trium, respectively. Salivary glands had the highest organ absorbed dose among all of the organs within the field. Larger FOVs yielded higher whole-body effective and organ absorbed doses compared with smaller FOVs. Conclusion: The results showed that using the ImPACT software to estimate the organ absorbed dose can serve as a suitable alternative to other costly and time-consuming methods available for this dose assessment in CBCT.

Background: This study intended to measure radiation doses to various organs and calculate the risk of cancer incidence from neck computed tomography and head computed tomography scans of trauma patients by using a thermoluminescent dosimeter. Methods: We assessed 93 patients who presented to the Emergency Department. Based on their health conditions, different computed tomography scans were performed. We used a fixed tube current of 200 mAs and tube voltage of 120 kVp for all patients. Next, we derived the effective radiation dose by multiplying the dose length product and conversion factor of each computed tomography scan based on the International Commission on Radiological Protection 103. Organ dose estimations were calculated from the dosimeter readout. We calculated the life attributable risk for cancer incidence based on the Committee on the Biological Effects of Ionizing Radiation VII preferred models. Results: Neck computed tomography scans had a mean effective dose of 2. 18 mSv. The mean effective dose for head computed tomography scans was 1. 53 mSv. The highest mean equivalent organ dose was for the thyroid with the neck computed tomography scan and the lenses of the eyes with the head computed tomography scan. There was no significant difference between scan lengths in each computed tomography acquisition. There was a noticeable correlation observed between effective radiation dose and tube current. As anticipated, young people had a higher life attributable risk of cancer compared to the elderly. This amount was less than 0. 011 per 100 persons for both computed tomography studies. Conclusion: Our data showed a significant organ radiation dose in both neck and head computed tomography scans, not only for the thyroid and the lenses of the eyes, but also for the chest.