Effect of CT electron density identification on Monte Carlo simulations of radiotherapeutic treatments

Introduction: The accurate identification of tissue electron densities is of great importance for Monte Carlo (MC) dose calculations. When converting patient CT data into a voxelised format suitable for MC simulations, however, it is common to simplify the assignment of electron densities so that the complex tissues existing in the human body are categorized into a few basic types. This study examines the effects that the assignment of tissue types and the calculation of densities can have on the results of MC simulations, for the particular case of a Siemen’s Sensation 4 CT scanner located in a radiotherapy centre where QA measurements are routinely made using 11 tissue types (plus air). Methods: DOSXYZnrc phantoms are generated from CT data, using the CTCREATE user code, with the relationship between Hounsfield units (HU) and density determined via linear interpolation between a series of specified points on the ‘CT-density ramp’ (see Figure 1(a)). Tissue types are assigned according to HU ranges. Each voxel in the DOSXYZnrc phantom therefore has an electron density (electrons/cm3) defined by the product of the mass density (from the HU conversion) and the intrinsic electron density (electrons /gram) (from the material assignment), in that voxel. In this study, we consider the problems of density conversion and material identification separately: the CT-density ramp is simplified by decreasing the number of points which define it from 12 down to 8, 3 and 2; and the material-type-assignment is varied by defining the materials which comprise our test phantom (a Supertech head) as two tissues and bone, two plastics and bone, water only and (as an extreme case) lead only. The effect of these parameters on radiological thickness maps derived from simulated portal images is investigated. Results & Discussion: Increasing the degree of simplification of the CT-density ramp results in an increasing effect on the resulting radiological thickness calculated for the Supertech head phantom. For instance, defining the CT-density ramp using 8 points, instead of 12, results in a maximum radiological thickness change of 0.2 cm, whereas defining the CT-density ramp using only 2 points results in a maximum radiological thickness change of 11.2 cm. Changing the definition of the materials comprising the phantom between water and plastic and tissue results in millimetre-scale changes to the resulting radiological thickness. When the entire phantom is defined as lead, this alteration changes the calculated radiological thickness by a maximum of 9.7 cm. Evidently, the simplification of the CT-density ramp has a greater effect on the resulting radiological thickness map than does the alteration of the assignment of tissue types. Conclusions: It is possible to alter the definitions of the tissue types comprising the phantom (or patient) without substantially altering the results of simulated portal images. However, these images are very sensitive to the accurate identification of the HU-density relationship. When converting data from a patient’s CT into a MC simulation phantom, therefore, all possible care should be taken to accurately reproduce the conversion between HU and mass density, for the specific CT scanner used. Acknowledgements: This work is funded by the NHMRC, through a project grant, and supported by the Queensland University of Technology (QUT) and the Royal Brisbane and Women's Hospital (RBWH), Brisbane, Australia. The authors are grateful to the staff of the RBWH, especially Darren Cassidy, for assistance in obtaining the phantom CT data used in this study. The authors also wish to thank Cathy Hargrave, of QUT, for assistance in formatting the CT data, using the Pinnacle TPS. Computational resources and services used in this work were provided by the HPC and Research Support Group, QUT, Brisbane, Australia.

The development of Monte Carlo techniques for the verification of radiotherapy treatments

Introduction: Recent advances in the planning and delivery of radiotherapy treatments have resulted in improvements in the accuracy and precision with which therapeutic radiation can be administered. As the complexity of the treatments increases it becomes more difficult to predict the dose distribution in the patient accurately. Monte Carlo (MC) methods have the potential to improve the accuracy of the dose calculations and are increasingly being recognised as the ‘gold standard’ for predicting dose deposition in the patient [1]. This project has three main aims: 1. To develop tools that enable the transfer of treatment plan information from the treatment planning system (TPS) to a MC dose calculation engine. 2. To develop tools for comparing the 3D dose distributions calculated by the TPS and the MC dose engine. 3. To investigate the radiobiological significance of any errors between the TPS patient dose distribution and the MC dose distribution in terms of Tumour Control Probability (TCP) and Normal Tissue Complication Probabilities (NTCP). The work presented here addresses the first two aims. Methods: (1a) Plan Importing: A database of commissioned accelerator models (Elekta Precise and Varian 2100CD) has been developed for treatment simulations in the MC system (EGSnrc/BEAMnrc). Beam descriptions can be exported from the TPS using the widespread DICOM framework, and the resultant files are parsed with the assistance of a software library (PixelMed Java DICOM Toolkit). The information in these files (such as the monitor units, the jaw positions and gantry orientation) is used to construct a plan-specific accelerator model which allows an accurate simulation of the patient treatment field. (1b) Dose Simulation: The calculation of a dose distribution requires patient CT images which are prepared for the MC simulation using a tool (CTCREATE) packaged with the system. Beam simulation results are converted to absolute dose per- MU using calibration factors recorded during the commissioning process and treatment simulation. These distributions are combined according to the MU meter settings stored in the exported plan to produce an accurate description of the prescribed dose to the patient. (2) Dose Comparison: TPS dose calculations can be obtained using either a DICOM export or by direct retrieval of binary dose files from the file system. Dose difference, gamma evaluation and normalised dose difference algorithms [2] were employed for the comparison of the TPS dose distribution and the MC dose distribution. These implementations are spatial resolution independent and able to interpolate for comparisons. Results and Discussion: The tools successfully produced Monte Carlo input files for a variety of plans exported from the Eclipse (Varian Medical Systems) and Pinnacle (Philips Medical Systems) planning systems: ranging in complexity from a single uniform square field to a five-field step and shoot IMRT treatment. The simulation of collimated beams has been verified geometrically, and validation of dose distributions in a simple body phantom (QUASAR) will follow. The developed dose comparison algorithms have also been tested with controlled dose distribution changes. Conclusion: The capability of the developed code to independently process treatment plans has been demonstrated. A number of limitations exist: only static fields are currently supported (dynamic wedges and dynamic IMRT will require further development), and the process has not been tested for planning systems other than Eclipse and Pinnacle. The tools will be used to independently assess the accuracy of the current treatment planning system dose calculation algorithms for complex treatment deliveries such as IMRT in treatment sites where patient inhomogeneities are expected to be significant. Acknowledgements: Computational resources and services used in this work were provided by the HPC and Research Support Group, Queensland University of Technology, Brisbane, Australia. Pinnacle dose parsing made possible with the help of Paul Reich, North Coast Cancer Institute, North Coast, New South Wales.

The role of perceived usefulness and attitude on electronic health record acceptance : an empirical investigation using response surface analysis

Information and communications technologies are a significant component of the healthcare domain and electronic health records play a major role within it. As a result, it is important that they are accepted en masse by healthcare professionals. How healthcare professionals perceive the usefulness of electronic health records and their attitudes towards them have been shown to have significant effects on their overall acceptance. This paper investigates the role of perceived usefulness and attitude on the intention to use electronic health records by future healthcare professionals using polynomial regression with response surface analysis. Results show that the relationship is more complex than predicted in prior research. The paper concludes that the predicting properties of the above determinants must be further investigated to clearly understand their role in predicting the intention to use electronic health records and in designing systems that are better adopted by healthcare professionals of the future.

The effect of hydroxyl groups and surface area of hematite derived from annealing goethite for phosphate removal

Synthetic goethite and thermally treated goethite at different temperatures were used to remove phosphate from sewage. The effect of annealing temperature on phosphate removal over time was investigated. X-ray diffraction(XRD), transmission electron microscopy (TEM), N2 adsorption and desorption (BET), and infrared emission spectrum (FT-IES) were utilized to characterize the phase, morphology, specific surface area, pore distribution, and the surface groups of samples. The results show that annealed products of goethite at temperatures over 250 °C are hematite with the similar morphology as the original goethite with different hydroxyl groups and surface area. Increasing temperature causes the decrease in hydroxyl groups, consequential increase in surface area at first and then experiences a decrease (14.8–110.4–12.6 m2/g) and the subsequent formation of nanoscale pores. The variation rate of hydroxyl groups and surface area based on FT-IES and BET, respectively, are used to evaluate the effect of annealing temperature on phosphate removal. By using all of the characterization techniques, it is concluded that the changes of phosphate removal basically result from the total variation rate between hydroxyl groups and surface area.

Investigation of ultra trace detection in functionalised-surface enhanced Raman spectroscopy (SERS)

We have developed an explanation for ultra trace detection found when using Au/Ag SERS nanoparticles linked to biochemical affinity tags, e.g. antibodies. The nanoparticle structure is not as usually assumed and the aggregated nanoparticles constitute hot spots that are indispensable for these very low levels of analyte detection, even more so when using a direct detection method.

Mesenchymal stem cells and nano-structured surfaces

Mesenchymal stem cells (MSCs) represent multipotent stromal cells that can differentiate into a variety of cell types, including osteoblasts (bone cells), chondrocytes (cartilage cells), and adipocytes (fat cells). Their multi-potency provides a great promise as a cell source for tissue engineering and cell-based therapy for many diseases, particularly bone diseases and bone formation. To be able to direct and modulate the differentiation of MSCs into the desired cell types in situ in the tissue, nanotechnology is introduced and used to facilitate or promote cell growth and differentiation. These nano-materials can provide a fine structure and tuneable surface in nanoscales to help the cell adhesion and promote the cell growth and differentiation of MSCs. This could be a dominant direction in future for stem cells based therapy or tissue engineering for various diseases. Therefore, the isolation, manipulation, and differentiation of MSCs are very important steps to make meaningful use of MSCs for disease treatments. In this chapter, we have described a method of isolating MSC from human bone marrow, and how to culture and differentiate them in vitro. We have also provided research methods on how to use MSCs in an in vitro model and how to observe MSC biological response on the surface of nano-scaled materials.

Comprehensive study of surface chemistry of MCM-41 using 29Si CP/MAS NMR, FTIR, pyridine-TPD, and TGA

A comprehensive study was conducted on mesoporous MCM-41. Spectroscopic examinations demonstrated that three types of silanol groups, i.e., single, (SiO)3Si-OH, hydrogen-bonded, (SiO)3Si-OH-OH-Si(SiO)3, and geminal, (SiO)2Si(OH)2, can be observed. The number of silanol groups/nm2, ?OH, as determined by NMR, varies between 2.5 and 3.0 depending on the template-removal methods. All these silanol groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol-1, respectively. However, only free silanol groups (involving single and geminal silanols) are highly accessible to the silylating agent, chlorotrimethylsilane. Silylation can modify both the physical and chemical properties of MCM-41.

Quantitative morphometric examination of the human pubic symphyseal surface of Australian individuals with age using computed tomography

Current forensic practice in age estimation relies on the application of morphological standards as a means to characterize complex threedimensional skeletal surfaces. Research in our laboratory has demonstrated that the application of the morphologically based Suchey-Brooks method to a contemporary Queensland, Australian population demonstrated significant inaccuracy in age-estimation. Consequently, this study presents preliminary results to quantify age-related skeletal changes of the pubic symphysis in Queensland individuals using novel geometric and micro-architectural protocols that have the potential of improving age estimation in the forensic context. Computed tomography scans of the right and left pubis were obtained from Caucasian individuals aged 15–70 years (n=195) from the Queensland Health Forensic and Scientific Services. Morphometric variables including surface area, circumference, maximum height and width of the symphyseal surface, and micro-architectural assessment of cortical and trabecular bone structure were conducted in Rapidform XOS and Osteomeasure, respectively. Morphometric analysis demonstrated increases in maximum height and width of the surface with age independent of gender, with most significant (P<0.05) changes between the 25–34 and 55–64 year subsets. Sexual dimorphism and bilateral asymmetry were prominent features in the Queensland population. Micro-architectural analysis demonstrated degradation of cortical composition with age, with differential bone resorption between the medial, ventral and dorsal aspects of the symphysis. The ability to quantitatively model age-related changes to the pubic symphysis provides potential for future methodological refinement, where rigor and robust geometric assessment of the surface may remove the subjectivity associated with aging the pubic symphysis.

Evaluation of the Suchey-Brooks method for aging Australian Caucasian Populations using multislice Computed Tomography reconstructions of the Pubic Symphyseal Surface

Establishing age-at-death for skeletal remains is a vital component of forensic anthropology. The Suchey-Brooks (S-B) method of age estimation has been widely utilised since 1986 and relies on a visual assessment of the pubic symphyseal surface in comparison to a series of casts. Inter-population studies (Kimmerle et al., 2005; Djuric et al., 2007; Sakaue, 2006) demonstrate limitations of the S-B method, however, no assessment of this technique specific to Australian populations has been published. Aim: This investigation assessed the accuracy and applicability of the S-B method to an adult Australian Caucasian population by highlighting error rates associated with this technique. Methods: Computed tomography (CT) and contact scans of the S-B casts were performed; each geometrically modelled surface was extracted and quantified for reference purposes. A Queensland skeletal database for Caucasian remains aged 15 – 70 years was initiated at the Queensland Health Forensic and Scientific Services – Forensic Pathology Mortuary (n=350). Three-dimensional reconstruction of the bone surface using innovative volume visualisation protocols in Amira® and Rapidform® platforms was performed. Samples were allocated into 11 sub-sets of 5-year age intervals and changes associated with the surface geometry were quantified in relation to age, gender and asymmetry. Results: Preliminary results indicate that computational analysis was successfully applied to model morphological surface changes. Significant differences in observed versus actual ages were noted. Furthermore, initial morphological assessment demonstrates significant bilateral asymmetry of the pubic symphysis, which is unaccounted for in the S-B method. These results propose refinements to the S-B method, when applied to Australian casework. Conclusion: This investigation promises to transform anthropological analysis to be more quantitative and less invasive using CT imaging. The overarching goal contributes to improving skeletal identification and medico-legal death investigation in the coronial process by narrowing the range of age-at-death estimation in a biological profile.

Inhibition of platelet aggregation and 5-HT release by extracts of Australian plants used traditionally as headache treatments

To identify potential migraine therapeutics, extracts of eighteen plants were screened to detect plant constituents affecting ADP induced platelet aggregation and [14C]5-hydroxytryptamine (5-HT) release. Extracts of the seven plants exhibiting significant inhibition of platelet function were reanalysed in the presence of polyvinyl pyrrolidone (PVP) to remove polyphenolic tannins that precipitate proteins. Two of these extracts no longer exhibited inhibition of platelet activity after removal of tannins. However, extracts of Crataegus monogyna, Ipomoea pes-caprae, Eremophila freelingii, Eremophila longifolia, and Asteromyrtus symphyocarpa still potently inhibited ADP induced human platelet [14C]5-HT release in vitro, with levels ranging from 62 to 95% inhibition. I. pes-caprae, and C. monogyna also caused significant inhibition of ADP induced platelet aggregation. All of these plants have been previously used as traditional headache treatments, except for C. monogyna which is used primarily for protective effects on the cardiovascular system. Further studies elucidating the compounds that are responsible for these anti-platelet effects are needed to determine their exact mechanism of action.

NSAM-derived total surface area vs. SMPS-derived "mobility equivalent" surface area for different environmentally relevant aerosols

The surface area of inhaled particles deposited in the alveolar region, as reported by the TSI nanoparticle surface area monitor (NSAM), was compared with the corresponding value estimated by a TSI scanning mobility particle sizer (SMPS) for a range of environmentally relevant aerosols, including petrol emissions, ETS, laser printer emissions, cooking emissions and ambient aerosols. The SMPS values were based on a mobility size distribution assuming spherical particles using the appropriate size-dependent alveolar-deposition factors provided by the ICRP. In most cases, the two instruments showed good linear agreement. With petrol emissions and ETS, the linearity extended to over 103 μm2 cm-3. With printer emissions, there was good linearity up to about 300 μm2 cm-3 while the NSAM increasingly overestimated the surface area at higher concentrations. The presence of a nucleation event in ambient air caused the NSAM to over-estimate the surface area by a factor of 2. We summarize these results and conclude that the maximum number concentration up to which the NSAM is accurate clearly depends on the type of aerosol being sampled and provide guidance for the use of the instrument.

Bending properties of Ag nanowires with pre-existing surface defects

Materials used in the engineering always contain imperfections or defects which significantly affect their performances. Based on the large-scale molecular dynamics simulation and the Euler–Bernoulli beam theory, the influence from different pre-existing surface defects on the bending properties of Ag nanowires (NWs) is studied in this paper. It is found that the nonlinear-elastic deformation, as well as the flexural rigidity of the NW is insensitive to different surface defects for the studied defects in this paper. On the contrary, an evident decrease of the yield strength is observed due to the existence of defects. In-depth inspection of the deformation process reveals that, at the onset of plastic deformation, dislocation embryos initiate from the locations of surface defects, and the plastic deformation is dominated by the nucleation and propagation of partial dislocations under the considered temperature. Particularly, the generation of stair-rod partial dislocations and Lomer–Cottrell lock are normally observed for both perfect and defected NWs. The generation of these structures has thwarted attempts of the NW to an early yielding, which leads to the phenomenon that more defects does not necessarily mean a lower critical force.

The effect of surface tension and kinetic undercooling on a radially-symmetric melting problem

The addition of surface tension to the classical Stefan problem for melting a sphere causes the solution to blow up at a finite time before complete melting takes place. This singular behaviour is characterised by the speed of the solid-melt interface and the flux of heat at the interface both becoming unbounded in the blow-up limit. In this paper, we use numerical simulation for a particular energy-conserving one-phase version of the problem to show that kinetic undercooling regularises this blow-up, so that the model with both surface tension and kinetic undercooling has solutions that are regular right up to complete melting. By examining the regime in which the dimensionless kinetic undercooling parameter is small, our results demonstrate how physically realistic solutions to this Stefan problem are consistent with observations of abrupt melting of nanoscaled particles.

Effects of hyperbaric oxygen and inducible nitric oxide synthase inhibitor treatment on femoral head osteonecrosis in a rat model

Introduction: Apoptosis is the final destiny of many cells in the body, though this process has been observed in some pathological processes. One of these pathological processes is femoral head non-traumatic osteonecrosis. Among many pro/anti-apoptotic factors, nitric oxide has recently been an area of further interest. Osteocyte apoptosis and its relation to pro-apoptotic action invite further research, and the inducible form of nitric oxide synthase (iNOS)—which produces a high concentration of nitric oxide—has been flagged. The aim of this study was to investigate the effect of hyperbaric oxygen (HBO) and inducible NOS suppressor (Aminoguanidine) in prevention of femoral head osteonecrosis in an experimental model of osteonecrosis in spontaneous hypertensive rats (SHRs). Methods: After animal ethic approval 34 SHR rats were divided into four groups. Ten rats were allocated to the control group without any treatment, and eight rats were allocated to three treatment groups namely: HBO, Aminoguanidine (AMG), and the combination of HBO and AMG treatments (HBO+AMG). The HBO group received 250 kPa of oxygen via hyperbaric chamber for 30 days started at their 5th week of life; the AMG group received 1mg/ml of AMG in drinking water from the fifth week till the 17th week of life; and the last group received a combination of these treatments. Rats were sacrificed at the end of the 17th week of life and both femurs were analysed for evidence of osteonecrosis using Micro CT scan and H&E staining. Also, osteocyte apoptosis and the presence of two different forms of NOS (inducible (iNOS) and endothelial (eNOS)) were analysed by immunostaining and apoptosis staining (Hoechst and TUNEL). Results: Bone morphology of metaphyseal and epiphyseal area of all rats were investigated and analysed. Micro CT findings revealed significantly higher mean fractional trabecular bone volume (FBV) of metaphyseal area in untreated SHRs compared with all other treatments (HBO, P<0.05, HBO+AMG, P<0.005, and AMG P<0.001). Bone surface to volume ratio also significantly increased with HBO+AMG and AMG treatments when compared with the control group (18.7 Vs 20.8, P<0.05, and 18.7 Vs 21.1, P<0.05). Epiphyseal mean FBV did not change significantly among groups. In the metaphyseal area, trabecular thickness and numbers significantly decreased with AMG treatment, while trabecular separation significantly increased with both AMG and HBO+AMG treatment. Histological ratio of no ossification and osteonecrosis was 37.5%, 43.7%, 18.7% and 6.2% of control, HBO, HBO+AMG and AMG groups respectively with only significant difference observed between HBO and AMG treatment (P<0.01). High concentration of iNOS was observed in the region of osteonecrosis while there was no evidence of eNOS activity around that region. In comparison with the control group, the ratio of osteocyte apoptosis significantly reduced in AMG treatment (P<0.005). We also observed significantly fewer apoptotic osteocytes in AMG group comparing with HBO treatment (P<0.05). Conclusion: None of our treatments prevents osteonecrosis at the histological or micro CT scan level. High concentration of iNOS in the region of osteonecrosis and significant reduction of osteocyte apoptosis with AMG treatment were supportive of iNOS modulating osteocyte apoptosis in SHRs.

Correcting radiation survey data to account for increased leakage during intensity modulated radiotherapy treatments

Purpose Intensity modulated radiotherapy (IMRT) treatments require more beam-on time and produce more linac head leakage to deliver similar doses to conventional, unmodulated, radiotherapy treatments. It is necessary to take this increased leakage into account when evaluating the results of radiation surveys around bunkers that are, or will be, used for IMRT. The recommended procedure of 15 applying a monitor-unit based workload correction factor to secondary barrier survey measurements, to account for this increased leakage when evaluating radiation survey measurements around IMRT bunkers, can lead to potentially-costly over estimation of the required barrier thickness. This study aims to provide initial guidance on the validity of reducing the value of the correction factor when applied to different radiation barriers (primary barriers, doors, maze walls and other walls) by 20 evaluating three different bunker designs. Methods Radiation survey measurements of primary, scattered and leakage radiation were obtained at each of five survey points around each of three different radiotherapy bunkers and the contribution of leakage to the total measured radiation dose at each point was evaluated. Measurements at each survey point were made with the linac gantry set to 12 equidistant positions from 0 to 330o, to 25 assess the effects of radiation beam direction on the results. Results For all three bunker designs, less than 0.5% of dose measured at and alongside the primary barriers, less than 25% of the dose measured outside the bunker doors and up to 100% of the dose measured outside other secondary barriers was found to be caused by linac head leakage. Conclusions Results of this study suggest that IMRT workload corrections are unnecessary, for 30 survey measurements made at and alongside primary barriers. Use of reduced IMRT workload correction factors is recommended when evaluating survey measurements around a bunker door, provided that a subset of the measurements used in this study are repeated for the bunker in question. Reduction of the correction factor for other secondary barrier survey measurements is not recommended unless the contribution from leakage is separetely evaluated.