Mathematical Phantom Research Articles

Gold nanoparticle effect on dose and DNA damage enhancement in the vicinity of gold nanoparticles

This study uses Monte Carlo simulations to examine the dose enhancement effect of gold nanoparticles (AuNPs) in radiation therapy and its effects on DNA damage. Using the GATE- 9.0 and Geant4-DNA packages, Monte Carlo simulations were used to simulate a mathematical phantom and determine the energy deposition in the vicinity of AuNP. The simulations were conducted for various photon beam energies (50, 100, 250, and 6000 keV) with and without the presence of different-size AuNPs (10, 30, 50 and 100 nm). The dose enhancement factor (DER) was evaluated using Geant4-DNA to examine the effects AuNP sizes and photon beam energies on DNA damage. A multi-scale Monte Carlo simulation was conducted to evaluate enhanced DNA damage owing to nanoparticles in the proximity of cancer cells. The Monte Carlo simulations indicated that AuNPs boost the dose delivery, resulting in enhanced energy deposition and subsequent DNA damage. The DER analysis revealed a significant increase in the dose deposition within DNA, leading to single or double-strand breaks. Geant4-DNA simulations revealed information on the dosage enhancement factor for various AuNP sizes and photon beam intensities, enabling a deeper comprehension of the underlying mechanics. The outcomes of this study emphasize the potential of AuNPs as effective radiosensitizers in radiation therapy and contribute to the growing body of research on the use of nanotechnology in enhancing cancer treatment outcomes. Further investigations and experimental validations are necessary to optimize the usage of AuNPs for improved radiation therapy.

A Monte Carlo simulation-based decision support system for radiation oncologists in the treatment of glioblastoma multiforme.

In the present research, we have developed a model-based crisp logic function statistical classifier decision support system supplemented with treatment planning systems for radiation oncologists in the treatment of glioblastoma multiforme (GBM). This system is based on Monte Carlo radiation transport simulation and it recreates visualization of treatment environments on mathematical anthropomorphic brain (MAB) phantoms. Energy deposition within tumour tissue and normal tissues are graded by quality audit factors which ensure planned dose delivery to tumour site thereby minimising damages to healthy tissues. The proposed novel methodology predicts tumour growth response to radiation therapy from a patient-specific medicine quality audit perspective. Validation of the study was achieved by recreating thirty-eight patient-specific mathematical anthropomorphic brain phantoms of treatment environments by taking into consideration density variation and composition of brain tissues. Dose computations accomplished through water phantom, tissue-equivalent head phantoms are neither cost-effective, nor patient-specific customized and is often less accurate. The above-highlighted drawbacks can be overcome by using open-source Electron Gamma Shower (EGSnrc) software and clinical case reports for MAB phantom synthesis which would result in accurate dosimetry with due consideration to the time factors. Considerable dose deviations occur at the tumour site for environments with intraventricular glioblastoma, haematoma, abscess, trapped air and cranial flaps leading to quality factors with a lower logic value of 0. Logic value of 1 depicts higher dose deposition within healthy tissues and also leptomeninges for majority of the environments which results in radiation-induced laceration.

A study on out-of-field leakage of an accelerator-based neutron beam for boron neutron capture therapy.

More and more accelerator-based boron neutron capture therapy (AB-BNCT) facilities are under the construction or commissioning stage, and the neutron beam characteristic measurements at each facility will start soon. In addition to the in-field neutron beam properties, the leakage of neutron beam is also important, which is related to the side effects of the patient. In the Virtual Technical Meeting on Advances in Boron Neutron Capture Therapy held by International Atomic Energy Agency (IAEA) in July 2020, the issue of the out-of-field leakage in BNCT was addressed. Heron Neutron Medical Corporation has been working on the beam design for China Medical University Hsinchu Hospital AB-BNCT research center. To evaluate the out-of-field leakage, both beam profile analysis and whole-body dose calculation are performed. An Oak Ridge National Laboratory (ORNL) Medical Internal Radiation Dose (MIRD) mathematical phantom is used to calculate the whole-body dose. For the estimated irradiation time which is set to be the time required for 80% of tumor dose to reach 20 Gy-w, the relative biological effectiveness weighted dose of abdomen region is less than 40 mGy-w and the whole-body dose is 104 mSv. The beam profile calculational result shows that the neutron ambient dose equivalent at 15 cm from the field edge is 11 mSv/Gy-w and drops to 5 mSv/Gy-w at 26 cm from the field edge. The gamma ray ambient dose equivalent is less than 1 mSv/Gy-w starting from 10 cm from the field edge. Although the neutron out-of-field leakage of the beam design is higher than that of the initially proposed guideline by IAEA in 2020, the whole-body dose, however, is reasonably low. Both the whole-body dose evaluation and the beam profile analysis are useful in the beam design consideration. The whole-body dose calculation together with the beam profile analysis can also be helpful in reaching an acceptable recommendation for the out-of-field leakage for BNCT neutron beam, a job wished to be accomplished in the near future as proposed in the 2023 IAEA's report on Advances in Boron Neutron Capture Therapy.

Computing thickness of irregularly-shaped thin walls using a locally semi-implicit scheme with extrapolation to solve the Laplace equation: Application to the right ventricle

Cardiac Magnetic Resonance (CMR) Imaging is currently considered the gold standard imaging modality in cardiology. However, it is accompanied by a tradeoff between spatial resolution and acquisition time. Providing accurate measures of thin walls relative to the image resolution may prove challenging. One such anatomical structure is the cardiac right ventricle. Methods for measuring thickness of wall-like anatomical structures often rely on the Laplace equation to provide point-to-point correspondences between both boundaries. This work presents limex, a novel method to solve the Laplace equation using ghost nodes and providing extrapolated values, which is tested on three different datasets: a mathematical phantom, a set of biventricular segmentations from CMR images of ten pigs and the database used at the RV Segmentation Challenge held at MICCAI’12. Thickness measurements using the proposed methodology are more accurate than state-of-the-art methods, especially with the coarsest image resolutions, yielding mean L1 norms of the error between 43.28% and 86.52% lower than the second-best methods on the different test datasets. It is also computationally affordable. Limex has outperformed other state-of-the-art methods in classifying RV myocardial segments by their thickness.

РАЗРАБОТКА ПРОГРАММНЫХ СРЕДСТВ МАТЕМАТИЧЕСКОГО ИМИТАЦИОННОГО МОДЕЛИРОВАНИЯ НА ОСНОВЕ КЛИНИЧЕСКИХ ДАННЫХ И ФАНТОМНЫХ ИССЛЕДОВАНИЙ ДЛЯ ОЦЕНКИ ПЕРФУЗИИ ГОЛОВНОГО МОЗГА И ПОВЫШЕНИЯ КАЧЕСТВА ИЗОБРАЖЕНИЙ ПРИ ОФЭКТ/КТ С 99MTC-ГМПАО

Purpose: To develop a software package Virtual examination of brain perfusion by the method of SPECT/CT with 99mTc-HMPAO (Teoxime) and its practical application to study the conditions for achieving the best image quality in clinical studies of patients. Material and methods: The studies were performed using clinical data and the method of computer simulation. Clinical data of single-photon emission computed tomography combined with X-ray computed tomography (SPECT/CT) with 99mTc-hexamethylpropyleneamine oxime (99mTc-Teoxime, produced by DIAMED LLC) of a patient with an ischemic stroke of the right frontal cortex were obtained on a two-detector gamma-camera NM/CT 670 DR GE Discovery (USA) using high-resolution low-energy collimators (LEHR). The measured data were processed using specialized software Q.Brain and Q.Volumetrix MI on a Xeleris 4.0 DR workstation from GE Healthcare (USA) to obtain reconstructed axial tomographic slices. To carry out simulation computer simulation of the procedure of examination of perfusion of GM by the method of SPECT/CT has developed a software package that includes a mathematical Hoffman phantom with the ability to simulate clinical cases of hypoperfusion of different localization and size (Virtual Patient), modeling the collection of “raw” projection data and an image reconstruction program based on the OSEM algorithm (Ordered Subset Expectation Maximization). An important advantage of the mathematical modeling method is the ability to assess the quality of the reconstructed image by calculating the root-mean-square error when compared with a given phantom. In numerical experiments, the dependence of the reconstruction error on the parameters of the OSEM algorithm (on the number of subgroups – subsets, and on the number of iterations) was investigated in order to determine the conditions for achieving the best image quality. A statistical stop criterion was developed and tested. Results: For the first time, a software package was developed and tested that allows us to investigate errors in the reconstruction algorithm, which is a great difficulty when using clinical research methods. A criterion for stopping iterations is proposed when using the OSEM reconstruction algorithm – minimizing the functional deviation of the chi-square function from the target value, while the detector pixels with non-zero values are combined into blocks according to the 2×2 scheme. There is a reliable good correlation between the proposed stop criterion and the minimum of the root-mean-square error of image reconstruction. This makes it possible to introduce this criterion into the clinical practice of using computational tools for reconstructing sections of the SPECT to obtain the best image. The simulation results demonstrated the possibility of reducing the time of data recording, during which the patient must remain motionless, at least twice. Conclusion: The method of computer simulation developed in this work is a practically useful technology that helps optimize the use of SPECT to achieve the best possible results of brain imaging in patients.

Digital reference objects for evaluating algorithm performance in MR image formation

PurposeDigital Reference Objects (DROs) are mathematical phantoms that can serve as a basis for evaluating MR image quality (IQ) in an objective way. Their main purpose is to facilitate the establishment of fully automated and perfectly reproducible IQ metrics to objectively compare different algorithms in MR image formation in a standardized manner. They also allow to re-build parts of standard phantoms. MethodsWe sample DROs directly in k-space, using analytical formulas for the continuous Fourier transform of primitive shapes. We demonstrate this DRO approach by applying a state-of-the-art CNN-based denoising algorithm that is robust to varying noise levels to noisy images of the resolution section of the well-known ACR phantom for IQ assessment, reconstructed from both measured and simulated k-space data. ResultsApplying the CNN-based denoising algorithm to the measured and simulated version of the ACR phantom resolution section produced virtually identical results, as confirmed by visual and quantitative comparison. ConclusionsDROs can help guide technology selection during the development of new algorithms in MR image formation, e.g., via deep learning. This could be an important step towards reproducible MR image formation.

Evaluation of organ and effective doses using anthropomorphic phantom: A comparison between experimental measurement and a commercial dose calculator

IntroductionThe aim of this study was to experimentally measure organ doses for computed tomography (CT) procedures using thermoluminescence dosimeters (TLDs) on a RANDO anthropomorphic phantom and verify the measured doses using CT-Expo software. MethodsThe phantom was irradiated using clinical CT scan protocols routinely used for specific procedures in the radiology department. Fifty TLD chips were used in this study. The scanning parameters (kVp, mA, s) used to scan the phantom were used as input parameters for CT-Expo dose estimations. ResultsThe TLD measured organ doses varied between 3.97 mGy for the esophagus and 56.22 mGy for the brain. High doses were recorded in the brain (37.80–56.22 mGy) and the eye lens (29.94–36.16 mGy). Comparing the organ dose measurements between TLD and CT-Expo, the maximum organ dose difference was obtained for the eye lens. A comparison between the two methods for the other organs were all less than 32 %. The effective doses from the TLD measurements for the head, chest, and abdominopelvic CT examinations were 2.78, 6.67, and 17 mSv, respectively and CT-Expo were 2.20, 10.30, and 16.70 mSv, respectively. ConclusionThe experimental and computational results are comparable, and the reliability of the TLD measurements and CT-Expo dose calculator has been proven. Implications for studyA reason for the difference in dose measurements between the two methods has been attributed to the dissimilarity in the organ position in the Rando anthropomorphic phantom and the standard mathematical phantom used by CT-Expo. The experimental and computational results have been found to be comparable.

Detection Limit of a NaI(Tl) Survey Meter to Measure <sup>131</sup>I Accumulation in Thyroid Glands of Children after a Nuclear Power Plant Accident

Background: This study examined the detection limit of thyroid screening monitoring conducted at the time of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 using a Monte Carlo simulation.Materials and Methods: We calculated the detection limit of a NaI(Tl) survey meter to measure 131I accumulation in the thyroid gland of children. Mathematical phantoms of 1- and 5-year-old children were developed in the simulation of the Particle and Heavy Ion Transport code System code. Contamination of the body surface with eight radionuclides found after the FDNPP accident was assumed to have been deposited on the neck and shoulder area.Results and Discussion: The detection limit was calculated as a function of ambient dose rate. In the case of 40 Bq/cm2 contamination on the body surface of the neck, the present simulations showed that residual thyroid radioactivity corresponding to thyroid dose of 100 mSv can be detected within 21 days after intake at the ambient dose rate of 0.2 μSv/hr and within 11 days in the case of 2.0 μSv/hr. When a time constant of 10 seconds was used at the dose rate of 0.2 μSv/hr, the estimated survey meter output error was 5%. Evaluation of the effect of individual differences in the location of the thyroid gland confirmed that the measured value would decrease by approximately 6% for a height difference of ±1 cm and increase by approximately 65% for a depth of 1 cm.Conclusion: In the event of a nuclear disaster, simple measurements carried out using a NaI(Tl) scintillation survey meter remain effective for assessing 131I intake. However, it should be noted that the presence of short-half-life radioactive materials on the body surface affects the detection limit.

A comparison of different detection techniques for 137Cs measurements of cattle in vivo.

Agricultural lands with farm animals (e.g. cattle) can be significantly affected by radioactive contamination following nuclear or radiation accidents. In order to optimise the techniques for measuring 137Cs in contaminated cattle, selected radiation detectors have been tested and calibrated using volumetric radiation sources. In addition, a mathematical phantom of a cow was created within Monte Carlo simulations. The main aim of the research was to propose a method for making rapid measurements of 137Cs in cattle in vivo/in situ and to select the most suitable measurement set-up. Measurements of contaminated cattle in vivo were carried out in Belarus with one selected detector, and were then compared with measurements of meat in a laboratory and with measurements of a control group of cows. The proposed measurement method was also tested on measurements of 137Cs in wild boars in Czechia with higher levels of the 137Cs activity.

New operational quantities (RBE × D p lens/Φ) for eye lens neutron dosimetry as a function of energy and angle of incidence in the ICRU 95 formalism

This paper is a continuation of a study published recently by the authors. It presents and discusses computed personal absorbed dose in the lens of the eye (D p lens/Φ), and a relative biological effectiveness (RBE)-weighted absorbed dose (in terms of an newly proposed operational quantity RBE × D p lens/Φ), conversion coefficients for the lens of the eye for neutron exposure at incident energies from thermal to ∼20 MeV and at angles of incidence from 0° to 90° in 15° increments, at 180° and for rotational incidence irradiation geometry (from 0° to 360° in 5° increments). These conversion coefficients were obtained from a simulation model developed for this study that contains the stylised eye model, embedded in the adult UF-ORNL mathematical phantom, whereby the previously stated RBE-weighted absorbed dose was obtained using the proposed RBE versus neutron energy distribution compiled in a previous paper by the authors. The simulations carried out for this study using the Monte Carlo N-Particle transport code version 6.2, were conducted in a realistic human eye model, for the left and right sensitive and whole volume of the lens of the eye, considering the recent proposed redefinition of the operational quantities for external radiation exposure in International Commission on Radiation Units and Measurements (ICRU) report 95. A comprehensive set of tabulated data for neutron fluence-to-dose conversion coefficients (D p lens/Φ in pGy cm2) and RBE-weighted absorbed dose (RBE × D p lens/Φ in pGy cm2) conversion coefficients is included in this paper as a function of incident neutron energy and angle of incidence. Data for D p lens/Φ (pGy cm2) are compared to similar data from the literature for validation of our model. Data for RBE × D p lens/Φ (in pGy cm2), were also compared to the equivalent operational quantity H p(3,α)/Φ (in pSv cm2) conversion coefficients calculated at 3 mm depth in a cylindrical phantom for different incident neutron energies and angles of incidence from 0° to 75° in 15° increments to demonstrate the relevance of this newly proposed operational quantity for doses resulting in tissue reactions (deterministic effects) which should be quoted in Gray (RBE-weighted absorbed dose, RBE × D (Gy)), rather than Sievert (Sv) which is reserved for stochastic effects. The current neutron weighted absorbed dose (RBE × D p lens) is proposed for the tissue reactions in the eye-lens for neutron radiation as per National Council on Radiation Protection and Measurements report 180 and in line with the recent proposal for the review and revision of the System of Radiological Protection to Keeping the International Commission on Radiological Protection (ICRP) recommendations fit for purpose. This method would bring better alignment between the dose limits in ICRP 118 and the new operational quantity consistent with the units of the new eye-lens dose limits without being overly conservative. The utilization of the proposed new operational quantities, as outlined in ICRU 95, has the potential to address the ongoing challenge in enforcing regulatory limits for neutron eye dose, specifically the use of Gy instead of Sv. It should be noted that the applicability of this will vary from country to country as in many countries the legislation is likely to mandate the use of H p(3) until the regulation is amended. This approach can serve as an interim solution while awaiting the issuance of the new ICRP general recommendations, which is expected to take several years. Implementing the new operational quantities can contribute to enhancing the accuracy and effectiveness of neutron eye dose limit enforcement.

Quantitative analysis of small coronary artery calcium detectability with an accurate simulation and validation on a clinical CT scanner.

The absence of coronary artery calcium (CAC) measured via CT is associated with very favorable prognosis, and current guidelines recommend low-density lipoprotein cholesterol (LDL-c) lowering therapy for individuals with any CAC. This motivates early detection of small granules of CAC; however, calcium scan sensitivity for detecting very low levels of calcium has not been quantified. In this work, the size limit of detectability of small calcium hydroxyapatite (CaHA) granules with clinical CAC scanning was assessed using validated simulations. CT projections of digital 3D mathematical phantoms containing small CaHA granules were simulated analytically; images were reconstructed using a filter designed to reproduce the point spread function of a specific commercial scanner, and a relationship of HU number versus diameter was derived. These simulation results were validated with experimental measurements of HU versus diameter from phantoms containing small granules of CaHA on a GE Revolution CT scanner in the clinic; ground truth measurements of the CaHA granule diameters were obtained using a Zeiss Xradia 510 Versa high-resolution 3D micro-CT imaging system. Using experimental measurements on the clinical CT scanner, detectability was quantified with a detectability index (d') using a non-prewhitened matched filter. The effect of changes to reconstruction slice thickness and reconstruction kernel on granule detectability was evaluated. Under typical clinical calcium scanning and reconstruction conditions, the minimum detectable diameter of a simulated spherical calcium granule with a clinically relevant CaHA density was 0.76mm. The minimum detectable volume was 2.4 times smaller on images reconstructed at a slice thickness of 0.625mm compared to 2.5mm. The detectability index d' increased by a factor of 1.7 when images were reconstructed with 0.625mm slices compared to 2.5mm slices. d' did not change when images were reconstructed with the high-resolution BONE filter compared to the less sharp STANDARD resolution filter on the GE Revolution CT. We have quantified detectability versus size of small calcium granules at the resolution limit of a widely available clinical CT scanner. Detectability increased significantly with reduced slice thickness and did not change with a sharper reconstruction kernel. The simulation can be used to calculate the trade-off between dose and CAC detectability.

An iterative reconstruction algorithm based on total nuclear variation for multi-channel EPRI

Oxygen concentration in tumor is a key information for effective radiation therapy. Electron paramagnetic resonance imaging (EPRI) is an advanced oxygen imaging technique. However, in the case of multi-channel EPRI， traditional imaging methods including filtered back-projection (FBP) and optimization algorithm related to total variation (TV) only consider the features of individual channel images and ignore the similarities among images of each channel. Total nuclear variation encourages shared edge positions and consistent gradient directions across multi-channel images. In this study, we propose a data divergence constrained, total nuclear variation minimization model and its Chambolle-Pock solving algorithm. We validate the accuracy of the algorithm and analyze its convergence through simulation studies using mathematical phantoms that simulate T1-weighted EPRI. Furthermore, we investigate the influence of algorithm parameters on convergence rate and evaluate the algorithm’s capability for sparse reconstruction and noise suppression. The experimental results show that the total nuclear variation minimization algorithm promotes edge structure information and gradient direction within individual channels of images. As a result, this algorithm successfully preserves essential image features while achieving accurate image reconstruction.

A Novel Method to Model Image Creation Based on Mammographic Sensors Performance Parameters: A Theoretical Study.

Mammographic digital imaging is based on X-ray sensors with solid image quality characteristics. These primarily include (a) a response curve that yields high contrast and image latitude, (b) a frequency response given by the Modulation Transfer Function (MTF), which enables small detail imaging and (c) the Normalize Noise Power Spectrum (NNPS) that shows the extent of the noise effect on image clarity. In this work, a methodological approach is introduced and described for creating digital phantom images based on the measured image quality properties of the sensor. For this purpose, a mathematical phantom, simulating breast tissue and lesions of blood, adipose, muscle, Ca and Ca(50%)-P(50%) was created by considering the corresponding X-ray attenuation coefficients. The simulated irradiation conditions of the phantom used four mammographic spectra assuming exponential attenuation. Published data regarding noise and blur of a commercial RadEye HR CMOS imaging sensor were used as input data for the resulting images. It was found that the Ca and Ca(50%)-P(50%) lesions were visible in all exposure conditions. In addition, the W/Rh spectrum at 28 kVp provided more detailed images than the corresponding Mo/Mo spectrum. The presented methodology can act complementarily to image quality measurements, leading to initial optimization of the X-ray exposure parameters per clinical condition.

In silico analysis of optimum photon energy spectra and beam parameters for iodine nanoparticle–aided orthovoltage radiation therapy of brain tumors

In this study, the effect of photon energy spectra on the dose enhancement factor (DEF) and other influencing parameters such as skull–tumor dose ratios were estimated for a confined tumor loaded with iodine nanoparticles (INPs). A mathematical brain phantom with a brain tumor was simulated by the MCNP6 Monte Carlo code. A validated commercial computed tomography model consisting of an X-ray tube, Al–Cu filters, and collimators was used to simulate the rotational conformal treatment of the tumor. INPs with a diameter of 20 nm and concentrations of 10–50 mg/g were introduced inside the tumor as homogenously distributed spherical particles. The dose distribution inside the phantom was scored for several orthovoltage beams with the peak voltages of 140, 200, and 320 kVp as well as two 3.5 and 6 MV megavoltage beams. A significant rise of DEF values with nanoparticle (NP) concentration for orthovoltage beams is revealed; no significant dose enhancement was obtained for megavoltage beams. The highest DEF and skull–tumor dose ratio were obtained for the 140 kVp beam which decreased with the number of directional fields. The clinically optimal plan for a brain tumor, with high DEFs of 2.81–2.24 and acceptable skull–tumor dose ratios of 0.61–0.51, would be feasible for treatment using 200 and 320 kVp beams, an iodine concentration of 20 mg/g, and 8–15 fields. Our calculations show that clinically significant radiation dose enhancements can be obtained for tumors loaded with INPs using orthovoltage beams. Optimal treatment regimens are feasible using a proper selection of photon beam spectrum and sufficient numbers of cross-firing beams. The limiting effect of skull bone could be minimized by increasing the number of radiation fields and the use of higher quality of orthovoltage beams.

Radiation hazard assessments of natural radioactivity in clay-based cosmetic products in Malaysia

Natural sources such as clays, plant extracts, and raw materials containing naturally occurring radioactive material (NORM) have been used as ingredients for medicinal and cosmetic purposes since ancient times. Nowadays, a variety of commercially available cosmetics products used clay minerals containing NORMs as the main formulation, which poses unknown radiation risks to the consumer. In this study, 11 samples of clay-based cosmetic products were used to conduct dose assessments on members of the public for various usage scenarios to evaluate the external exposure dose. Gamma-ray spectroscopy was utilised to measure the activity concentrations of 238U, 232Th, and 40K in the sample. Meanwhile, doses to skin and other organs from these cosmetic products were modelled using Geant4 Monte Carlo simulations and the MIRD5 mathematical phantom, incorporating dose conversion factors (DCFs). The results revealed that the activity concentration for 238U, 232Th, and 40K ranged from 0.1 – 1.3, 0.06–15.6, and 0.22–6.9 Bq g−1, respectively, which were lower than the reference provided by the international regulation. The analysis for heavy metals showed that sample 9 contained a high amount of Cd, which gave an immediate alert to that particular product. Furthermore, the effective doses in the skin estimated in this study with the range of 2.7–240 μSv y−1, were significantly lower than the International Commission on Radiological Protection (ICRP) reference limit of 50 mSv per year for members of the general public. Based on the few μSv of effective dose exposure, it is sufficient to conclude that the dose from these products poses no radiological risk to the user. The addition of NORMs in cosmetic products should be done with caution because higher concentrations can raise the dose.

On the operational quantity for eye lens neutron dosimetry considering ICRU 95 report

For planned occupational exposure situations, the International Commission on Radiological Protection (ICRP) publication 118 recommends an equivalent dose limit for the lens of the eye of 20 mSv yr−1 averaged over 5 yr with no single year exceeding 50 mSv. Regulatory authorities of various jurisdictions worldwide followed some or all, of the ICRP recommendations and implemented reduced occupational lens of eye dose limits in their legislation. As compliance with the eye-lens dose limit will be based on the summation of doses received from all types of radiation, applicable to a variety of workplaces, the contribution of neutrons to eye lens dose will be important where it contributes a significant fraction of the total dose to the eye lens. This work presents and discusses computed personal absorbed dose (D lens/Φ), and personal dose equivalent (H p(3)/Φ) as well as a newly proposed relative biological effectiveness (RBE)-weighted absorbed dose (RBE × D lens/Φ) conversion coefficients for the lens of the eye for neutron exposure at incident energies from thermal to ∼20 MeV. The D lens/Φ coefficients were obtained from a simulation model developed for this study that contains the stylised eye model embedded in the adult UF-ORNL mathematical phantom. The modelling techniques used in these simulations were also used to calculate H p(3)/Φ for the International Commission on Radiation Units and Measurements (ICRU) slab and cylinder phantoms. All simulations carried out for this study utilised the Monte Carlo N-Particle (MCNP) series of codes. The results are compared with the related published data. The issue of compliance with the current equivalent dose limit for the lens of the eye is addressed from a neutron perspective considering the recent proposed redefinition of the operational quantities for external radiation exposure in ICRU report 95. The use of a radiation weighted absorbed dose (RBE × D lens, in Gy) is proposed for the tissue reactions in the eye-lens for neutron radiation as per the National Council on Radiation Protection and Measurements report 180, and in line with the recent review and revision of the System of Radiological Protection To Keeping the ICRP Recommendations Fit for Purpose, which states that RBE weighted dose should be used for high-Linear energy transfer (LET) radiations such as neutrons. This confirms the earlier statement in ICRP publication 92, paragraph 297 and reiterated in the Executive summary, paragraph (q) of ICRP publication 118. The proposed approach would provide an operational quantity consistent with the units of the new eye-lens dose limits without being overly conservative.

Development of anthropomorphic mathematical phantoms for simulations of clinical cases in diagnostic nuclear medicine

ABSTRACT We seek to propose a new generation of mathematically stylised phantoms with high levels of anatomical detail for the purposes of SPECT and PET simulations. Two basic phantoms were created: a mathematical model of the torso (MMT) and a mathematical model of the whole body (MMB). The phantoms can be manipulated by varying the position, size and shape of bones and organs to simulate patients with anatomical variants. Verification of the developed phantoms was performed by comparing simulated planar images for MMT and MMB with clinical data. Both phantoms did produce realistic planar images, which closely mimic real clinical planar images. Images obtained in computer simulation of myocardial perfusion SPECT with virtual patient (MMT) demonstrate the same errors and interpretation problems that exist in clinical routine. These phantoms can be used for simulations of clinical cases to help medical experts to understand the causes of artefacts and bias in PET and SPECT images.

On the caregiver effective dose analysis during I‑131 therapy in different situations using two mathematical phantoms and Monte Carlo code

On the caregiver effective dose analysis during I‑131 therapy in different situations using two mathematical phantoms and Monte Carlo code

Pixel-driven computation of parallel and fan-beam projections of a digital image based on pixel-representation using a new formula

BackgroundThe computation of the projections of a digital image – modelled as a superposition of square pixels – is essential in several algorithms in computed tomography, and also in many machine vision applications. Projections of digital images are computed through the ray-driven approach. Current pixel-driven methods, though simpler, involve interpolation kernels in the projection-domain – not based on the exact Radon transform (RT) of a square. MethodsA new analytical formula – for the line-integral of the unit pixel – simpler than that published previously, is derived. The formula allows easy, pixel-driven computation of the RT of a digital image based on the pixel model i.e., Riemann-sum approximation to the line integral. The method naturally allows pixel-driven backprojection, based on the same (pixel) model. The approach is extended to computing projections over divergent (fan-) beams, and its application as a generalized version of the traditional Hough transform, is discussed. ResultsThe Radon transform of the unit-pixel match that of a digital square image. The RT, of a mathematical phantom consisting of a superposition of elliptical disks, compares well with that based on analytical formula. A comparative study with the pixel driven approach with interpolation in the projection-domain, and its important variant, is included. The fan-beam projections of the square image and the phantom are presented. The applicability of the RT in estimating the Hough transform over precise lines, is shown. ConclusionThe new formula, a simplified version of that of Deans, is useful in pixel-driven computation of parallel and fan-beam projections based on Riemann-sum approximation, which is exact in the case of the common pixel-based image model. Pixel-driven approach is amenable to parallel, and also region-of-interest computation. The method is useful in CT as well as machine vision applications.

Foam-like phantoms for comparing tomography algorithms.

Tomographic algorithms are often compared by evaluating them on certain benchmark datasets. For fair comparison, these datasets should ideally (i) be challenging to reconstruct, (ii) be representative of typical tomographic experiments, (iii) be flexible to allow for different acquisition modes, and (iv) include enough samples to allow for comparison of data-driven algorithms. Current approaches often satisfy only some of these requirements, but not all. For example, real-world datasets are typically challenging and representative of a category of experimental examples, but are restricted to the acquisition mode that was used in the experiment and are often limited in the number of samples. Mathematical phantoms are often flexible and can sometimes produce enough samples for data-driven approaches, but can be relatively easy to reconstruct and are often not representative of typical scanned objects. In this paper, we present a family of foam-like mathematical phantoms that aims to satisfy all four requirements simultaneously. The phantoms consist of foam-like structures with more than 100000 features, making them challenging to reconstruct and representative of common tomography samples. Because the phantoms are computer-generated, varying acquisition modes and experimental conditions can be simulated. An effectively unlimited number of random variations of the phantoms can be generated, making them suitable for data-driven approaches. We give a formal mathematical definition of the foam-like phantoms, and explain how they can be generated and used in virtual tomographic experiments in a computationally efficient way. In addition, several 4D extensions of the 3D phantoms are given, enabling comparisons of algorithms for dynamic tomography. Finally, example phantoms and tomographic datasets are given, showing that the phantoms can be effectively used to make fair and informative comparisons between tomography algorithms.