Dose evaluation of the one-year-old child in PET imaging by18F-(DOPA, FDG, FLT, FET) and68Ga-EDTA using reference voxel phantoms.

Because of more sensitive organs due to high growth rates, evaluating the absorbed dose is essential for children to prevent irreparable damage. Therefore, to this aim, a one-year-old child's whole-body effective dose and organ absorbed dose were evaluated for various PET imaging Radiopharmaceuticals such as:18F-DOPA,18F-FDG,18F-FLT,18F-FET, and68Ga-EDTA. For this aim, one-year-old child reference voxel phantoms and GATE Monte Carlo simulation were used, and the results were compared with the ICRP128 report (for stylized phantom). The highest absorbed dose was related to bladder wall (for18F-DOPA,18F-FET, and68Ga-EDTA), heart wall (for18F-FDG), and liver (for18F-FLT) between 30 organs that have been studied. Comparing the results with the ICRP128 report values for a one-year-old child show a significant difference in some organs. Comparison of the effective dose with the ICRP128 report shows a relative difference of 22%, 12.5%, 11.8%, 10.8% and 8.6% for18F-DOPA,68Ga-EDTA,18F-FDG,18F-FET,18F-FLT, respectively. In conclusion, using new one-year-old voxel phantoms could provide a better estimate of organs absorbed dose and whole-body effective dose due to its exact structure.

Comparison between Targeted Radionuclide Therapy of Bone Metastases Based on ß-Emitting and α-Emitting Radionuclides.

INTRODUCTION: The α- and ß-emitter radionuclides are used for palliative treatment of bone metastasis. Our objective was to compare the dosimetric parameters of radionuclides used in bone pain palliation therapy. METHODS: Monte Carlo code, MCNPX, was used to simulate radiation transport. Dosimetric calculations were performed for monoenergetic electrons with energies of 0.1-3 MeV, α-particles with energies of 3-10 MeV, and several radionuclides 32P, 89Sr, 153Sm, 177Lu, 223Ra, and its progeny. The simulated phantom consisted of bone marrow, an endosteal layer, bone, and soft tissue. Source tissues included bone marrow, endosteal layer, and bone. Absorbed fractions and specific absorbed fractions were calculated for target regions. Absorbed doses were calculated for investigated radionuclides. RESULTS: The obtained results demonstrated that the dosimetric parameters vary depending on the source or target size, particle energy, and location of the source. The ß-emitter radionuclides were able to penetrate the bone marrow region, whereas the α-emitter radionuclides gave a higher and localized dose to the bone and endosteal layer in comparison. CONCLUSION: 223Ra and 177Lu have fewer side effects on the bone marrow, and they may be a better choice for use in bone pain palliation radiotherapy.

A Monte Carlo Simulation Study of Optimization for Collimator in a Pixelated SPECT Camera.

OBJECTIVE: To investigate the influence of collimator hole shape, size, and material on the performance of the high-resolution SPECT camera to find the optimal collimator design using the GEANT4 application for the tomographic emission Monte Carlo platform. METHODS AND MATERIALS: The geometry of the dual head camera equipped with a pixelated CsI(Na) crystal, lead hexagonal-hole collimator, and two flat-panel H8500 position-sensitive photomultipliers were accurately described in the GEANT4 application for the tomographic emission. The basic features of the scanner were calculated by using 2 mCi 99mTc sources. RESULTS: The simulated average spatial resolutions of lead hexagonal-, square-, and round-hole collimators were 2.68, 2.96, and 3.06 mm at 2.5 cm from the collimator surface, respectively. The sensitivity of the lead hexagonal-hole collimator was 10.86% and 18.84%, greater than that of the square and round holes, respectively, on the collimator surface. The measured averages of spatial resolution using gold were 16.14%, 11.39%, and 5.1% better than those of lead, tantalum, and tungsten hexagonal-hole collimators, respectively, at 2.5 cm from the collimator. The sensitivities of the tungsten, gold, tantalum, depleted uranium, and lead hexagonal-hole collimators were 0.74, 0.48, 1.127, 0.32, and 1.38 cps/µCi on the collimator surface, respectively. CONCLUSIONS: The hexagonal-hole collimator was preferred over the square- and round-hole collimators because of the optimum sensitivity and spatial resolution offered by its regular arrangement of apertures. Also, the lower-absorption and stopping-power materials such as lead revealed relatively better characteristics at specific sensitivity, whereas higher-absorption materials such as gold showed the best spatial resolution. The collimator with finer hole size had the superior spatial resolution and less sensitivity than larger holes.

An assessment of bone-seeking radionuclides for palliation of metastatic bone pain in a vertebral model.

OBJECTIVE: Bone-seeking radiopharmaceuticals have the main role in the treatment of painful bone metastases. The aim of this study was to dosimetrically compare radiopharmaceuticals in use for bone pain palliation therapy and bone scan. METHODS: The MCNPX code was used to simulate the radiation transport in a vertebral phantom. Absorbed fractions were calculated for monoenergetic electrons, photons and alpha particles. S values were obtained for radionuclides 32P, 33P, 89Sr, 90Y, 99mTc, 117mSn, 153Sm, 166Ho, 169Er, 177Lu, 186Re, 188Re, 223Ra, 224Ra and their progenies for target regions including the active marrow and the bone endosteum. RESULTS: The results demonstrated the dependence of dosimetric parameters on the source or target size, particle energy and location of the source. The electron emitters including 33P, 117mSn, 169Er and 177Lu and 223Ra as an α-emitter gave the lower absorbed dose to the active marrow. These radionuclides gave the highest values of the Relative Advantage Factor (RAF). CONCLUSIONS: According to the results, 33P, 117mSn, 169Er, 177Lu and 223Ra have fewer side effects on the active marrow than other investigated radionuclides. Therefore, these radionuclides may be a better choice for use in palliative radiotherapy.

Capabilities of the Monte Carlo Simulation Codes for Modeling of a Small Animal SPECT Camera.

PURPOSE: This study aims to compare Monte Carlo-based codes' characteristics in the determination of the basic parameters of a high-resolution single photon emission computed tomography (HiReSPECT) scanner. METHODS: The geometry of this dual-head gamma camera equipped with a pixelated CsI(Na) scintillator and lead hexagonal hole collimator were accurately described in the GEANT4 Application for the Tomographic Emission (GATE), Monte Carlo N-particle extended (MCNP-X), and simulation of imaging nuclear detectors (SIMIND) codes. We implemented simulation procedures similar to the experimental test for calculation of the energy spectra, spatial resolution, and sensitivity of HiReSPECT by using 99mTc sources. RESULTS: The energy resolutions simulated by SIMIND, MCNP-X, and GATE were 17.53, 19.24, and 18.26%, respectively, while it was calculated at 19.15% in experimental test. The average spatial resolutions of the HiReSPECT camera at 2.5 cm from the collimator surface simulated by SIMIND, MCNP-X, and GATE were 3.18, 2.9, and 2.62 mm, respectively, while this parameter was reported at 2.82 mm in the experiment test. The sensitivities simulated by SIMIND, MCNP-X, and GATE were 1.44, 1.27, and 1.38 cps/µCi, respectively, on the collimator surface. CONCLUSIONS: Comparison between simulation and experimental results showed that among these MC codes, GATE enabled to accurately model realistic SPECT system and electromagnetic physical processes, but it required more time and hardware facilities to run simulations. SIMIND was the most flexible and user-friendly code to simulate a SPECT camera, but it had limitations in defining the non-conventional imaging device. The most important characteristics like time and speed of simulation, preciseness of results, and user-friendliness should be considered during simulations.

Validation of GATE for bone and bone marrow with calculation specific absorbed fraction for photons.

PURPOSE: GATE/GEANT is a Monte Carlo code dedicated to nuclear medicine that allows calculation of the dose to organs (bone and bone marrow) of voxel phantoms. On the other hand, Medical Internal Radiation Dose (MIRD) is a well-developed system for estimation of the dose to human organs. In this study, results obtained from GATE/GEANT using leg of Snyder phantom is compared to published MIRD data. MATERIALS AND METHODS: For this, the mathematical leg of Snyder phantom was discretized and converted to a digital phantom of 100 × 100 × 200 voxels. The activity was considered uniformly distributed within bone and bone marrow. The GATE/GEANT Monte Carlo code was used to calculate the dose to the bone and bone marrow of the leg phantom from mono-energetic photons of 10, 15, 20, 30, 50, 100, 200, 500, and 1000 keV. The dose was converted into a specific absorbed fraction (SAF) and the results were compared to the corresponding published MIRD data. RESULTS: On average, there was a good correlation between the two series of data for self-absorption (r 2 = 0.99) and for cross-irradiation (r 2 = 0.99). However, the GATE/GEANT data were on average 1.01 ± 0.79% higher than the corresponding MIRD data for self-absorption. As for cross-irradiation, the GATE/GEANT data were on average 8.11 ± 7.95% higher than the MIRD data. CONCLUSION: In this study, the SAF values derived from GATE/GEANT and the corresponding MIRD published data were compared. On average, the SAF values derived with GATE/GEANT showed an acceptable correlation and agreement with the MIRD data for the photon energies of 50-1000 keV. For photons of 10-30 keV, there was an only poor agreement between the GATE/GEANT results and MIRD data.

Development of GATE Monte Carlo simulation for a CsI pixelated gamma camera dedicated to high resolution animal SPECT.

GATE is currently considered in scintigraphic imaging as a powerful tool to develop, design and optimize nuclear medicine modalities. This paper describes the GATE simulation of a pixelated gamma camera which is dedicated to high resolution of small animals imaging. It consists of a CsI(Na) crystal array coupled to position sensitive photomultiplier tube. The simulation model includes photon tracking through low energy high resolution hexagonal parallel holes collimator, CsI(Na) pixelated crystal, back-compartment, and camera shielding. Simulations were compared with experimental results by some criteria such as energy spectrum, energy resolution, spatial resolution, sensitivity and count profiles obtained from line and point sources imaging. The acquired energy resolution show good agreement with measured spectra. Difference between calculated and experimental values is about 0.3% for absolute sensitivity measurement. The result of the image uniformity is more consistent after implementation of non-uniformity correction. These values were about 1.3 and 1.2% for experimental and simulation study in the central field of view, respectively. Measurements showed that the spatial resolutions differences at the head surface along the long dimensions of gamma camera for simulation and experimental differed by no more than 4%.Differences along the short axis were about 6%. The FWHMs of images of point and line sources show good consistency between experimental images and corresponding simulated ones. The difference between experimental and simulated system parameters was within 11%. Our results demonstrate the ability and flexibility of the Monte Carlo simulation for modeling pixelated gamma camera with position sensitive detector by selecting the appropriate parameters for digitizer chain and collimator position on the detector surface.

Measurement of in-phantom neutron flux and gamma dose in Tehran research reactor boron neutron capture therapy beam line.

AIM: Determination of in-phantom quality factors of Tehran research reactor (TRR) boron neutron capture therapy (BNCT) beam. MATERIALS AND METHODS: The doses from thermal neutron reactions with 14N and 10B are calculated by kinetic energy released per unit mass approach, after measuring thermal neutron flux using neutron activation technique. Gamma dose is measured using TLD-700 dosimeter. RESULTS: Different dose components have been measured in a head phantom which has been designed and constructed for BNCT purpose in TRR. Different in-phantom beam quality factors have also been determined. CONCLUSIONS: This study demonstrates that the TRR BNCT beam line has potential for treatment of superficial tumors.

An Evaluation of the Organ Dose Received by Cardiologists Arising From Angiography Examinations in Educational Hospital in Rasht.

Interventional procedures, cine acquisitions and operation of fluoroscopic equipment in high-dose fluoroscopic modes, involve long fluoroscopic times which can lead to high staff doses. Also, Coronary angiography (CA) procedures require the cardiologist and assisting personnel to remain close to the patient, which is the main source of scattered radiation. Thus, radiation exposure is a significant concern for radiation workers and it is important to measure the radiation doses received by personnel and evaluate the parameters concerning total radiation burden. In this research, we investigated radiation doses to 10 cardiologists performing 120 CA procedures. Using thermo luminescent dosimeters doses to the wrists, thyroid and eyes per procedure were measured. Based on the measured dose values, maximum doses to the Left wrist, Right wrist, thyroid and eyes of cardiologist were measured 241.45 µSv, 203.17 µSv, 78.21 µSv and 44.58 µSv, respectively. The results of this study indicate that distance from the source, use of protective equipment's, procedure complexity, equipment performance, and cardiologist experience are the principal exposure-determining variables. It can be conclude that if adequate radiation protection approaches have been implemented, occupational dose levels to cardiologists would be within the regulated acceptable dose limits.

Evaluation of three scatter correction methods based on estimation of photopeak scatter spectrum in SPECT imaging: a simulation study.

Three practical methods for scatter correction of Tc-99m SPECT images are evaluated. Among these, two methods, three-energy window (TEW) methods using the trapezoidal and triangular approximations, have been described previously by investigators, and a new approximation is offered in this work. The SIMIND (SIMulation of Imaging Nuclear Detectors) Monte Carlo program is used to simulate a line source placed at on-axis and 5 cm off-axis locations, a cold-sphere/hot-background phantom, a hot-sphere/cold-background phantom, and a more clinically realistic NCAT (Nonuniform Rational B-spline-based CArdiac-Torso) phantom. For evaluation of these methods, the scatter line-spread functions and scatter fractions for the on- and off-axis line source, image contrast, signal-to-noise ratio and relative noise for the cold spheres, and recovery coefficient for the hot spheres of different diameters are compared. For the NCAT phantom, a line profile through a slice of the reconstructed image is considered before and after scatter correction, and also image contrast defined by this profile is used to compare the correction methods. The results of this study indicate that for the line source simulation the scatter fractions obtained from the proposed method are a better estimation of true scatter fractions. Also, for both the sphere simulation and NCAT simulation, the proposed method improves the image contrast as compared to the two other methods.

Evaluation of target dose based on water-equivalent thickness in external beam radiotherapy.

In vivo dosimetry was carried out for 152 patients receiving external beam radiotherapy and the treatment sites were divided into two main groups: Thorax, Abdomen, and Pelvic (120 fields) and Head and Neck (52 fields). Combined entrance and exit dose measurements were performed using LiF: Mg, Cu, P thermoluminescent dosimeters (TLDs). Water-equivalent (effective) thicknesses and target dose were evaluated using dose transmission data. The ratio of measured to expected value for each quantity was considered as an indicator for the accuracy of the parameter. The average ratio of the entrance dose was evaluated as 1.01 ± 0.07. In the diameter measurement, the mean ratio of effective depth divided by the contour depth is 1.00 ± 0.13 that shows a wide distribution which reflects the influence of contour inaccuracies as well as tissue inhomogeneities. At the target level, the mean ratio of measured to the prescribed dose is 1.00 ± 0.07. According to our findings, the difference between effective depth and patient depth has a direct relation to target dose discrepancies. There are some inevitable sources which may cause the difference. Evaluation and application of effective diameter in treatment calculations would lead to a more reliable target dose, especially for fields which involve Thorax, Abdomen, and Pelvic.

Evaluation of six scatter correction methods based on spectral analysis in (99m)Tc SPECT imaging using SIMIND Monte Carlo simulation.

Compton-scattered photons included within the photopeak pulse-height window result in the degradation of SPECT images both qualitatively and quantitatively. The purpose of this study is to evaluate and compare six scatter correction methods based on setting the energy windows in (99m)Tc spectrum. SIMIND Monte Carlo simulation is used to generate the projection images from a cold-sphere hot-background phantom. For evaluation of different scatter correction methods, three assessment criteria including image contrast, signal-to-noise ratio (SNR) and relative noise of the background (RNB) are considered. Except for the dual-photopeak window (DPW) method, the image contrast of the five cold spheres is improved in the range of 2.7-26%. Among methods considered, two methods show a nonuniform correction performance. The RNB for all of the scatter correction methods is ranged from minimum 0.03 for DPW method to maximum 0.0727 for the three energy window (TEW) method using trapezoidal approximation. The TEW method using triangular approximation because of ease of implementation, good improvement of the image contrast and the SNR for the five cold spheres, and the low noise level is proposed as most appropriate correction method.