GATE Monte Carlo Code Research Articles

Artificial High- and Low-density Materials in Bone Mineral Densitometry Using Dual-energy X-ray Absorptiometry: A GATE Monte Carlo Simulation of "Black-hole" Artifact.

The objective of the study was to evaluate the effect of artificial high- and low-density materials on Bone mineral density (BMD)scans in dual-energy X-ray absorptiometry (DXA) method and emergence of black-hole artifact through GATE Monte Carlo simulation. GATE Monte Carlo code was utilized to simulate the artifact encountered in clinical scans acquired by HOLOGIC® bone densitometer. Two simplified phantoms were designed. The first one was a rectangular box with six smaller cubes inside and the second one was a body torso. Materials of cubes were spine bone, polymethyl methacrylate (PMMA), barium sulfate suspension in water, stainless steel, titanium alloy, and gold. The torso phantom contained objects of 5 vertebrae, bowel and 3 small spherical objects near the surface of the torso as piercing objects on the abdominal wall, each overlying the vertebrae. Using 100 and 140 kVp, spectral X-rays were generated to simulate DXA. For both phantoms, two simulations were carried out. The pair of projections acquired for each phantom were then subtracted and analyzed by curve fitting techniques. Except for spine bone, in which radio-opacity decreases with increasing spectral X-ray energy (from 100 to 140 kVp), other squares exhibit little changes over different energies. PMMA shows consistently very low radio-opacity. Four other materials (barium sulfate in water, stainless steel alloy, titanium alloy, and gold), all attenuate the X-ray photons substantially. Except for spine bone, other materials are barely noticeable in pairwise subtracted images. In torso phantom, piercing objects are visualized as "holes" in vertebrae. Both artificial high- and low-density materials, compared to bone, are eliminated during the subtraction of dual-energy X-ray profiles and therefore, can create black-hole artifact.

PET/SPECT/spectral-CT/CBCT imaging in a small-animal radiation therapy platform: A Monte Carlo study-Part I: Quad-modal imaging.

In spite of the tremendous potential of game-changing biological image- and/or biologically guided radiation therapy (RT) and adaptive radiation therapy for cancer treatment, existing limited strategies for integrating molecular imaging and/or biological information with RT have impeded the translation of preclinical research findings to clinical applications. Additionally, there is an urgent need for a highly integrated small-animal radiation therapy (SART) platform that can seamlessly combine therapeutic and diagnostic capabilities to comprehensively enhance RT for cancer treatment. We investigated a highly integrated quad-modal on-board imaging configuration combining positron emission tomography (PET), single-photon emission computed tomography (SPECT), photon-counting spectral CT, and cone-beam computed tomography (CBCT) in a SART platform using a Monte Carlo model as a proof-of-concept. The quad-modal on-board imaging configuration of the SART platform was designed and evaluated by using the GATE Monte Carlo code. A partial-ring on-board PET imaging subsystem, utilizing advanced semiconductor thallium bromide detector technology, was designed to achieve high sensitivity and spatial resolution. On-board SPECT, photon-counting spectral-CT, and CBCT imaging were performed using a single cadmium zinc telluride flat detector panel. The absolute peak sensitivity and scatter fraction of the PET subsystem were estimated by using simulated phantoms described in the NEMA NU-4 standard. The spatial resolution of the PET image of the platform was evaluated by imaging a simulated micro-Derenzo hot-rod phantom. To evaluate the quantitative imaging capability of the system's spectral CT, the Bayesian eigentissue decomposition (ETD) method was utilized to quantitatively decompose the virtual noncontrast (VNC) electron densities and iodine contrast agent fractions in the Kidney1 inserts mixed with the iodine contrast agent within the simulated phantoms. The performance of the proposed quad-model imaging in the platform was validated by imaging a simulated phantom with multiple imaging probes, including an iodine contrast agent and radioisotopes of 18F and 99mTc. The PET subsystem demonstrated an absolute peak sensitivity of 18.5% at the scanner center, with an energy window of 175-560KeV, and a scatter fraction of only 3.5% for the mouse phantom, with a default energy window of 480-540KeV. The spatial resolution of PET on-board imaging exceeded 1.2mm. All imaging probes were identified clearly within the phantom. The PET and SPECT images agreed well with the actual spatial distributions of the tracers within the phantom. Average relative errors on electron density and iodine contrast agent fraction in the Kidney1 inserts were less than 3%. High-quality PET images, SPECT images, spectral-CT images (including iodine contrast agent fraction images and VNC electron density images), and CBCT images of the simulated phantom demonstrated the comprehensive multimodal imaging capability of the system. The results demonstrated the feasibility of the proposed quad-modal imaging configuration in a SART platform. The design incorporates anatomical, molecular, and functional information about tumors, thereby facilitating successful translation of preclinical studies into clinical practices.

Optimized Monte Carlo simulations for voxel-based internal dosimetry

Objective. The scientific community has considered internal dosimetry by the Monte Carlo method the gold standard. However, there is a trade-off between simulation processing time and the statistical quality of the results that makes it a challenge to obtain accurate absorbed dose values in some situations, such as dose estimation in organs affected by cross-irradiation or limited computing power. Variance reduction techniques are used to reduce computational processing time without impairing the statistical quality of the results, such as tracking energy cutoff, secondary particle production threshold, and parallelism of different types of emissions from radionuclides. Approach. In this work, GATE Monte Carlo code and its variance reduction techniques were evaluated to calculate S values of organs from the international commission on radiological protection (ICRP) report 110 male phantom for the lutetium-177, iodine-131, yttrium-90, and radium-223 radionuclides. The results are compared with the data from the OpenDose collaboration. Main results. A cutoff of 5 MeV for local electron deposition and 2.0 mm of secondary particle production range resulted in a computational efficiency increase of 7.9 and 1.05 times, respectively. Simulation of ICRP 107 spectra-based source proved to be about 5 times more efficient when compared to a decay simulation using G4RadioactiveDecay (Geant4-based radioactive decay processes). Track length estimator (TLE) and split exponential track length estimator (seTLE) techniques were used to calculate the absorbed dose of photon emissions, resulting in computational efficiency up to 29.4 and 62.5 times higher when compared to traditional simulations, respectively. In particular, the seTLE technique accelerates the simulation time by up to 1426 times, achieving a statistical uncertainty of 10% in volumes affected by cross-irradiation. Significance. The variance reduction techniques used in this work drastically reduced the simulation time and maintained the statistical quality of the calculated absorbed dose values, proving the feasibility of the use of the Monte Carlo method in internal dosimetry under challenging situations and making it viable for clinical routine or web applications.

The Feasibility of Quad-Modal PET/SPECT/Spectral-CT/CBCT On-Board Imaging in a Small-Animal Radiation Therapy Platform

<h3>Purpose/Objective(s)</h3> While radiation therapy (RT) paradigms have evolved rapidly, preclinical RT techniques, especially molecular/functional imaging guidance techniques, are still far behind, which hampers successful translation of novel RT techniques to bedside practices. In this study, we firstly investigated the feasibility of a highly integrated quad-modal on-board imaging configuration, including positron emission tomography (PET), single-photon emission computed tomography (SPECT), spectral CT, and cone-beam computed tomography (CBCT), in a small animal radiation therapy (SART) platform, which presents a near ideal one-stop comprehensive platform for preclinical RT studies. <h3>Materials/Methods</h3> The quad-modal imaging configuration in a SART platform was modeled by using the GATE Monte Carlo code as a proof-of-concept. A partial-ring on-board PET imaging subsystem was designed using a semiconductor thallium bromide detector. A single cadmium zinc telluride flat panel detector was utilized to obtain on-board SPECT, spectral-CT, and CBCT images of small animals. A preclinical SART workflow based on the quad-modal imaging guidance was designed, with image-guided RT and emission-guided radiation therapy (EGRT) incorporated as biologically guided RT modalities. The spatial resolution, sensitivity, and scatter fraction of the PET subsystem were measured using the simulated phantoms. To demonstrate the quad-model imaging performance of the platform, a simulated phantom with multiple imaging probes, including iodine and radioisotopes of ¹⁸F and ^99mTc, was imaged. In spectral CT imaging of the phantom, the virtual non-contrast (VNC) electron density and iodine uptake fractions in Kidney1 inserts, mixed with an iodine contrast agent at electron fractions of 0.02 and 0.03, were decomposed and imaged quantitatively by using the Bayesian eigentissue decomposition (ETD) method. <h3>Results</h3> For the PET subsystem, the spatial resolution was better than 1.2 mm, the absolute peak sensitivity at the platform center with an energy window of 175–560 KeV was 18.5%, and the measured scatter fraction was 3.5% for the mouse phantom described in the NEMA NU-4 standard with a default energy window of 480–540 KeV. In quad-model imaging of the phantom, all imaging probes, including iodine uptake fractions, were imaged clearly within the phantom. The PET and SPECT images of the phantom agreed well with the actual spatial distributions of the tracers within the phantom. The quantitative spectral-CT images of iodine uptake fraction and VNC electron density matched well with the ground truth values within a reasonable error range. <h3>Conclusion</h3> The results demonstrated the feasibility of the proposed quad-modal imaging configuration in a SART platform. With the anatomical, molecular, and functional information of tumors being accounted for, this novel design can improve the accuracy of preclinical RT studies, thereby facilitating the successful translation of preclinical studies to clinical practices.

Simulation of Slot-Scan imaging system with GATE and images quality evaluation

Interest in slot scanning imaging system has been increased recently because of its advantages such as high image resolution, reduction in patient dose and reduction in image distortion. The purpose of this study is to simulate a slot scanning imaging system using GATE multi-purpose Monte Carlo code and design an object phantom to evaluate image quality. The energy spectrum of X-ray in the radiological diagnostic range was simulated by GATE Monte Carlo code. An object phantom consisting of stripes with different thicknesses of copper was then designed to determine CNR and line pairs per millimeter to determine spatial resolution.The results showed that the simulated energy spectrum were in accordance with experiment. The evaluated parameters of image quality obtained from the simulations were compared with X-ray images using standard image quality criteria to determine the capabilities of the slot scanning imaging method. The spatial resolution of the simulated images was obtained to be 1.6 lp / mm for the slot scanning method, which is in the range of clinical radiology images. Therefore, this simulated model can be used to investigate and optimize other influential parameters such as filtration effect and collimator slit width effect, object distance to the detector ... in slot scanning imaging system.

Nanoscale energy deposition frequencies evaluation using GATE simulation tools

Over the last decade, cancer treatment with radiation therapy has evolved significantly due to the improvements in Treatment Planning Systems (TPS). Ideally, these algorithms can determine the dose distribution at the macroscopic scale. However, due to the lack of knowledge, these approaches remain impractical to model radiation side effects at the nanometric scale. This study presents the validation of Monte Carlo (MC) algorithms as a novel approach to model the nanodosimetric effects of radiation therapy particles on real DNA molecule models. A simulation of two simple volumes irradiated by a proton beam is performed to demonstrate the ability of the mixed Geant4-DNA physics model to describe extremely low-energy particle interactions compared to the simple standard Electromagnetic options three physic list. Furthermore, the nanodosimetric effects on the DNA molecule are simulated based on the calculations of the energy frequency deposited by both electron and proton beams in cylinders of three distinct nanometric diameters sizes corresponding to the block elements of the nucleus cell (10 bp, nucleosome, and chromatin fiber). Finally, following the results of this study, the energy deposition frequency in nanoscale cylinders simulated based on the Gate MC code is in good agreement with the results of the series of MOCA codes previously published in the literature.

Investigation of the dosimetric parameters of 125I BEBIG IsoSeed® I25.S06 source: GATE 8.2 Monte Carlo code

Permanent implantation of the iodine-125 brachytherapy sources is an irradiation technique for the treatment of the localized cancer. As described by the American Association of Physicists in Medicine (AAPM) Task group 43 (TG-43U1), it is crucial to determine the dose distribution around the brachytherapy seed before its effective clinical practice or even before releasing the sources for the treatment. In the present work, according to TG-43U1 report, the dosimetric parameters of BEBIG iodine-125 Low Dose Rate brachytherapy IsoSeed® I25.S06 source model was investigated. To perform the dose calculations, we have used GEANT4 Application for Emission Tomography (GATE) Monte Carlo simulations. Interesting results have been found. In particular, the dosimetric quantities like the radial dose function gL(r), the anisotropy function F(r,θ) and the dose rate constant Λ have been obtained. In addition, our data are in good agreement with the previous published works. It is also remarked that, GATE Monte Carlo code reproduces accurate dosimetric parameters results.

BEBIG 60Co HDR brachytherapy source dosimetric parameters validation using GATE Geant4-based simulation code

PurposeThis study aims to validate the dosimetric characteristics of High Dose Rate (HDR) 60Co source (Co0.A86 model) using GATE Geant4-based Monte Carlo code. According to the recommendation of the American Association of Physicists in Medicine (AAPM) task group report number 43, the dosimetric parameters of a new brachytherapy source should be verified either experimentally or by Monte Carlo calculation before clinical applications. The validated 60Co source in this study will be used for the simulation of intensity-modulated brachytherapy (IMBT) of vaginal cancer using the same GATE Geant4-based Monte Carlo code in the future. Materials and methodsGATE (version 9.0) simulation code was used to model and calculate the required TG-43U1 dosimetric data of the 60Co HDR source. DoseActors were defined for calculation of dose rate constant, radial dose function, and anisotropy function in a water phantom with an 80 cm radius. ResultsThe dose rate constant was obtained as 1.070±0.008cGy.h−1.U−1 which shows a relative difference of 2.01% compared to the consensus value, 1.092 ​cGy.h−1.U−1. The calculated results of anisotropy and radial dose functions starting from 0.1 cm to 10 cm around the source showed excellent agreement with the results of published studies. The mean variation of the radial dose and anisotropy functions values from the consensus data were 1% and 0.9% respectively. ConclusionFindings from this investigation revealed that the validation of the HDR 60Co source is feasible by the GATE Geant4-based Monte Carlo code. As a result, the GATE Monte Carlo code can be used for the verification of the brachytherapy treatment planning system.

Developing a protocol for 90Y bremsstrahlung imaging after Transarterial Radioembolization

Yttrium-90 (90Y) is an almost pure beta emitter used in Transarterial Radioembolization (TARE). Post-TARE 90Y bremsstrahlung imaging is employed for quantification of the delivered dose. 90Y bremsstrahlung imaging is the most challenging issue in nuclear medicine because of the low photon yield, the continuous and non-pronounced peak of the bremsstrahlung spectrum. GATE Monte Carlo code was employed to find the most proper imaging protocol for 90Y bremsstrahlung imaging. Images were acquired using Medium-Energy Medium-Resolution (MEMR) and High-Energy Medium-Resolution (HEMR) in nine energy windows widths (50 to 500 keV). The quality of images was evaluated using contrast, resolution, sensitivity, Signal-to-Background Ratio (SBR), percentage of total counts in useful field of view, and Contrast-to-Noise Ratio (CNR). The HEMR collimator performed better than the MEMR collimator on all imaging criteria except for the sensitivity. The CNR values were equal in both collimators. Based on the measured parameters, images acquired by the HEMR collimator with the energy window of 50–200 keV are the best protocol for 90Y bremsstrahlung imaging. The findings in this study suggest the imaging protocol for 90Y bremsstrahlung imaging that can be practically used in the clinic.

Development of GATE Monte Carlo Code for Simulation and Dosimetry of New I-125 Seeds in Eye Plaque Brachytherapy.

Dose distributions are calculated by Monte Carlo (MC) simulations for two low-energy models 125I brachytherapy source-IrSeed-125 and IsoAid Advantage (model IAI-125A)-loaded in the 14-mm standardized plaque of the COMS during treatment of choroid melanoma. In this study, at first, the radial dose function in water around 125I brachytherapy sources was calculated based on the recommendations of the Task Group No. 43 American Association of Physicists in Medicine (TG-43U1 APPM) using by GATE code. Then, brachytherapy dose distribution of a new model of the human eye was investigated for a 14-mm COMS eye plaque loaded with these sources with GATE Monte Carlo simulation. Results show that there are good agreements between simulation results of these sources and reporting measurements and simulations. Dosimetry results in the designed eye phantom for two types of iodine seeds show that the ratios of average dose of tumor to sclera, vitreous, and retina for IrSeed (IsoAid) source are 3.7 (3.7), 6.2 (6.1), and 6.3 (6.3), respectively, which represents the dose saving to healthy tissues. The maximum percentage differences between DVH curve of IsoAid and IrSeed seeds was about 8%. Our simulation results show that although new model of the 125I brachytherapy source having a slightly larger dimension than IAI-125A, it can be used for eye melanoma treatment because the COMS eye plaque loaded with IrSeed-125 could produce similar results to the IsoAid seeds, which is applicable for clinical plaque brachytherapy for uveal melanoma.

Dosimetry of Bone-Seeking Radiopharmaceuticals for Palliative Therapy of Bone Metastases: A Simulation Study Using GATE Monte Carlo Code

Purpose: Radiopharmaceutical Therapy (RPT) is one of the effective methods for pain palliation of bone metastases. Bone marrow is a critical organ in bone structure whose absorbed dose should be kept below a certain threshold. The purpose of this study was to calculate and compare absorbed doses of bone-seeking radiopharmaceuticals used in the palliative treatment of bone metastases. Materials and Methods: In this study, the GATE Monte Carlo code was used to simulate a femur bone, which consists of bone marrow, endosteal layer, bone, and soft tissue phantom model. Absorbed doses of the 153Sm-EDTMP, 89SrCl2, 177Lu-EDTMP, 188Re-HEDP, and 223RaCl2 radiopharmaceuticals were calculated in the femur phantom compartments. Results: bone absorbed doses per disintegration from alpha particles of 223RaCl2 is approximately 24 times higher than absorbed doses from beta particles of 89SrCl2. Also, absorbed dose per disintegration from beta particles of 89SrCl2 in the bone is approximately 12, 6 and 1.5 times higher than 177Lu-EDTMP, 153Sm-EDTMP, and 188Re-HEDP, respectively. Moreover, the bone and bone marrow absorbed dose from beta particles of 153Sm-EDTMP is 1.9 times higher than 177Lu-EDTMP. Besides, absorbed dose per disintegration from beta particles of 188Re-HEDP in the bone marrow is approximately 40, 30, 7, and 4 times higher than 223RaCl2, 89SrCl2, 177Lu-EDTMP and 153Sm-EDTMP, respectively. Conclusion: Our results show that 223RaCl2 could be a more efficient radiopharmaceutical for radionuclide therapy of bone metastases. Also, 177Lu-EDTMP, due to low marrow toxicity and comparable bone absorbed dose with 153Sm-EDTMP, can be used for achieving bone pain palliation. Moreover, significantly high bone marrow absorbed dose of 188Re-HEDP should be considered for palliative therapy of metastatic bone patients.

Bragg peak characteristics of proton beams within therapeutic energy range and the comparison of stopping power using the GATE Monte Carlo simulation and the NIST data

AbstractPurpose:To examine detail depth dose characteristics of ideal proton beams using the GATE Monte Carlo technique.Methods:In this study, in order to improve simulation efficiency, we used pencil beam geometry instead of parallel broad-field geometry. Depth dose distributions for beam energies from 5 to 250 MeV in a water phantom were obtained. This study used parameters namedRpeak,R90,R80,R73,R50, full width at half maximum (FWHM), width of 80–20% distal fall-off (W(80–20)) and peak-to-entrance ratio to represent Bragg peak characteristics. The obtained energy–range relationships were fitted into third-order polynomial formulae. The present study also used the GATE Monte Carlo code to calculate the stopping power of proton pencil beams in a water cubic phantom and compared results with the National Institute of Standards and Technology (NIST) standard reference database.Results:The study results revealed deeper penetration, broader FWHM and distal fall-off and decreased peak-to-entrance dose ratio with increasing beam energy. Study results for monoenergetic proton beams showed thatR73can be a good indicator to characterise a range of incident beams. These also suggest FWHM is more sensitive thanW(80–20)distal fall-off in finding initial energy spread. Furthermore, the difference between the obtained stopping power from simulation and NIST data almost in all energies was lower than 1%.Conclusion:Detail depth dose characteristics for monoenergetic proton beams within therapeutic energy ranges were reported. These results can serve as a good reference for clinical practitioners in their daily practice.

A GATE Monte Carlo model for a newly developed small animal PET scanner: the IRI-microPET

Abstract Monte Carlo simulation is widely used in emission tomography, in order to assess image reconstruction algorithms and correction techniques, for system optimization, and study the parameters affecting the system performance. In the current study, the performance of the IRI-microPET system was simulated using the GATE Monte Carlo code and a number of performance parameters, including spatial resolution, scatter fraction, sensitivity, RMS contrast, and signal-to-noise ratio, evaluated and compared to the corresponding measured values. The results showed an excellent agreement between simulated and measured data: The experimental and simulated spatial resolutions (radial) for 18F in the center of the AFOV were 1.81 mm and 1.65 mm, respectively. The difference between the experimental and simulated sensitivities of the system was &lt;7%. Simulated and experimental scatter fractions differed less than 9% for the mouse phantom in different timing windows. The validation study of the image quality indicated a good agreement in RMS contrast and signal-to-noise ratio. Also, system performance was compared with the two available commercial scanners which were simulated using GATE code. In conclusion, the assessment of the Monte Carlo modeling of the IRI-microPET system reveals that the GATE code is a flexible and accurate tool for describing the response of an animal PET system.

Radiation interaction parameters of commercial building glasses at energies of interest for potential nuclear accidents

AbstractElemental composition, mass attenuation coefficients (MACs), effective atomic numbers (EANs), and effective electron densities (EEDs) give information about the nuclear applications of materials (dosimetry, shielding, etc.). In this work, MAC of some commercial building glasses were determined using the WinXCom computer program and GATE Monte Carlo code; additionally,EAN and EED of these glasses were also determined using related formulas, after the elemental compositions of the samples were determined by energy dispersive X‐ray spectroscopy (EDS) technique. These properties were determined at 59.5 keV (Am‐241), 380 keV (Ir‐192), 662 keV (Cs‐237), 1173 keV (Co‐60), and 1332 keV (Co‐60). These energies are of interest for any potential nuclear accident. The elemental compositions show the presence of C, O, Na, Mg, Si, and Ca in various percentages; MAC values ranged from about 0.05 to 0.225 cm2/g; EAN also ranged from about 9 to 11and EED is almost constant at all energies considered except at 59.5 keV where higher values were shown. The radiation interaction properties of the investigated glasses showed that they could be used as a dosimeters during emergency radiation exposure situations.

Rabbit internal dosimetry for iodine-131 using GATE Monte Carlo simulation code: a preclinical trial

Introduction: One of the main concerns in administration of radiotracers, especially in therapeutic arm, is the amount of delivered dose to the different organs. Individual variations of anatomy, physiology and underlying pathology in the patients lead to alteration of administered activity. In the current study we preclinically applied internal dosimetry using an animal model Materials and Methods: The SPECT/CT imaging of a rabbit 24 hours after administration of 288μci Iodine-131 was done. Biodistribution of radiotracer was obtained from SPECT, and the CT was used to define attenuation map and the target volume of interest (VOIs). Dosimetry calculations were performed with GATE Monte Carlo code and S-values for beta and gamma radiation of different organs were calculated. Results: The S-values of thyroid as target organ are 1.09×10-4(mGy/MBq/sec) for beta and 1.05×10- 5 for gamma radiation. And S-values of kidneys, lungs, spine, and heart as critical organs are 1.10×10-5, 1.58×10-5, 7.62×10-6, 6.75×10-6 for beta, respectively and 3.9×10-6, 2.69×10-6, 2.63×10-6, 3.27×10-6 for gamma, respectively Conclusion: The internal dosimetry is applicable clinically. The response to therapy would be increased and the side effect would be minimized if the prescription using patient specific dosimetry is optimized.

Abstract ID: 118 Internal dosimetry of 68Ga-DOTATATE using Monte Carlo GATE simulation for XCAT phantom

Introduction Widespread use of FDG PET/CT imaging leads to improvement in non-FDG- avid somatostatin receptor imaging of tumor tissue. These synthetic somatostatin analogs can be labeled with β -emitting radionuclides, such as 68 Ga [1] , but estimating the absorbed dose in critical organs is important. The aim of this research is to calculate absorbed dose in all organs especially pituitary gland and thymus in 68 Ga-DOTATATE dosimetry. Materials and Methods Two total body male and female XCAT phantoms with 128 × 128 matrix size and 600 slices containing 1 mCi activity of 68 Ga was simulated. GATE Monte-Carlo code was employed for dosimetry calculations. Based on MIRD schema, we reported s-values of self-absorption and cross-irradiation in spleen, bladder, kidneys and liver, as well as cross-irradiation in pituitary gland and thymus. Results We reported the S-value for spleen, the most critical organ in 68 Ga-DOTATATE to be 13.7e−004 mGy/MBq-s and 15.6e−004 mGy/MBq-s in male and female phantom respectively. The highest amount of cross-irradiation in spleen is from kidney with the amount of 0.097e−004 mGy/MBq-s. The amount of self-absorption is in Bladder with 42.1e−004 mGy/MBq-s and 50e−004 mGy/MBq-s in male and female phantom respectively. The absorbed dose in thymus from spleen is 2.3710e−006 mGy/MBq-s in male and 3.1138e−006 mGy/MBq-s in female. Absorbed dose of pituitary gland from spleen is 0.53e−007 mGy/MBq-s. Conclusion We performed internal dosimetry using XCAT phantoms and GATE Monte-Carlo code for 68 Ga. Our results could be helpful in estimating absorbed dose in critical organs specially those not being considered in conventional methods.

The importance of BMI in dosimetry of 153Sm-EDTMP bone pain palliation therapy: A Monte Carlo study

Using digital phantoms as an atlas compared to acquiring CT data for internal radionuclide dosimetry decreases patient overall radiation dose and reduces the required analysis effort and time for organ segmentation. The drawback is that the phantom may not match exactly with the patient. We assessed the effect of varying BMIs on dosimetry results for a bone pain palliation agent, 153Sm-EDTMP.The simulation was done using the GATE Monte Carlo code. Female XCAT phantoms with the following different BMIs were employed: 18.6, 20.8, 22.1, 26.8, 30.3 and 34.7kg/m2. S-factors (mGy/MBq.s) and SAFs (kg−1) were calculated for the dosimetry of the radiation from major source organs including spine, ribs, kidney and bladder into different target organs as well as whole body dosimetry from spine. The differences in dose estimates from different phantoms compared to those from the phantom with BMI of 26.8kg/m2 as the reference, were calculated for both gamma and beta radiations. The relative differences (RD) of the S-factors or SAFs from the values of reference phantom were calculated.RDs greater than 10% and 100% were frequent in radiations to organs for photon and beta particles, respectively. The relative differences in whole body SAFs from the reference phantom were 15.4%, 7%, 4.2%, −9.8% and −1.4% for BMIs of 18.6, 20.8, 22.1, 30.3 and 34.7kg/m2, respectively. The differences in whole body S-factors for the phantoms with BMIs of 18.6, 20.8, 22.1, 30.3 and 34.7kg/m2 were 39.5%, 19.4%, 8.8%, −7.9% and −4.3%, respectively.The dosimetry of the gamma photons and beta particles changes substantially with the use of phantoms with different BMIs. The change in S-factors is important for dose calculation and can change the prescribed therapeutic dose of 153Sm-EDTMP. Thus a phantom with BMI better matched to the patient is suggested for therapeutic purposes where dose estimates closer to those in the actual patient are required.

A 3D Monte Carlo Method for Estimation of Patient-specific Internal Organs Absorbed Dose for (99m)Tc-hynic-Tyr(3)-octreotide Imaging.

Single-photon emission computed tomography (SPECT)-based tracers are easily available and more widely used than positron emission tomography (PET)-based tracers, and SPECT imaging still remains the most prevalent nuclear medicine imaging modality worldwide. The aim of this study is to implement an image-based Monte Carlo method for patient-specific three-dimensional (3D) absorbed dose calculation in patients after injection of 99mTc-hydrazinonicotinamide (hynic)-Tyr3-octreotide as a SPECT radiotracer. 99mTc patient-specific S values and the absorbed doses were calculated with GATE code for each source-target organ pair in four patients who were imaged for suspected neuroendocrine tumors. Each patient underwent multiple whole-body planar scans as well as SPECT imaging over a period of 1-24 h after intravenous injection of 99mhynic-Tyr3-octreotide. The patient-specific S values calculated by GATE Monte Carlo code and the corresponding S values obtained by MIRDOSE program differed within 4.3% on an average for self-irradiation, and differed within 69.6% on an average for cross-irradiation. However, the agreement between total organ doses calculated by GATE code and MIRDOSE program for all patients was reasonably well (percentage difference was about 4.6% on an average). Normal and tumor absorbed doses calculated with GATE were slightly higher than those calculated with MIRDOSE program. The average ratio of GATE absorbed doses to MIRDOSE was 1.07 ± 0.11 (ranging from 0.94 to 1.36). According to the results, it is proposed that when cross-organ irradiation is dominant, a comprehensive approach such as GATE Monte Carlo dosimetry be used since it provides more reliable dosimetric results.

Validation of the gate Monte Carlo code for radiation therapy and application to inhomogeneities

Introduction The treatment planning system (TPS), used in most cases, is based on fast and accurate analytical algorithms for dose estimation. However, limitations appear in inhomogeneous environments with strong gradient of density, as in the lungs. Monte Carlo solutions exist for complicated treatment with high inhomogeneity, such as the gold-standard BEAMnrc/EGSnrc. Nevertheless, the computation times are too long for routine use. In order to implement other Monte Carlo codes for external radiation therapy, our study focuses on the validation of GATE/ GEANT4. Materials and methods The linear medical accelerator CLINAC 2100C (Varian) from Belfort-Montbeliard hospital is modelised in GATE 6.2 for a 6 MV photon beam. The reference measurements are determined by two types of ionization chambers (PTW 31002 and PTW 31014) and are compared with the results of the both Monte Carlo codes (GATE and BEAMnrc). Once GATE has been validated, the performance of both codes will be evaluated in the inhomogeneities (dentures). Results The simulation parameters of GATE were adjusted to validate the accelerator modeling from percentage depth dose and profiles in the reference conditions. The results of the both codes with high density inhomogeneities are close. Conclusion The accelerator model was validated using GATE. The first analyses about the inhomogeneities give promising results. Thereafter, the evaluation of the code will go on more complex models (anthropomorphic phantom, breathing 4D phantom) always using BEAMnrc as a reference.

Investigation of the potential use of LaBr 3:Ce scintillators for scintimammography imaging

The motivation of this study is to exploit the high light yield and excellent energy resolution of LaBr 3:Ce scintillators compared with NaI(Tl) crystal in scintimammograpic imaging systems. A dedicated gamma camera and 3D phantom were modelled using GATE Monte Carlo code under a variety of imaging situations including lession sizes, tumour activity-to-background ratios and tumour depths. The major finding of the present study is that LaBr 3:Ce crystal-based cameras have the potential to detect small lesions (≤10 mm) at clinical TBR.