ABSTRACT
Background: South Africa has high tobacco-attributable mortality and a smoking prevalence of 32.5% in males and 25.6% in females. There are limited data on smoking prevalence and desire to quit in hospitalised patients, who have limited access to smoking cessation services. Objectives: To determine smoking prevalence and the extent of nicotine withdrawal symptoms, using a hospital-wide inpatient survey. Methods: A 1-day point prevalence survey was conducted at Groote Schuur Hospital, Cape Town. All wards except the haematology isolation, active labour and psychiatry lock-up wards were evaluated. Smoking status, withdrawal symptoms and desire to quit were established. Results: Smoking status was confirmed in 85.8% of inpatients (n=501/584), of whom 31.9% (n=160) were current smokers; 43.5% (n=101/232) of male and 21.9% (n=59/269) of female inpatients were smokers. Documentation and confirmation of smoking status was highest in the maternity wards (100%) and lowest in the surgical wards (79.6%) and intensive care units (70.0%). Smoking prevalence ranged from 47.6% in male surgical patients to 15.2% in maternity patients. Of the smokers, 54.5% reported being motivated to quit, with a median (interquartile range) Fagerström test for nicotine dependence score of 4 (2 - 6), and 31.4% reported moderate to severe cravings to smoke, highest in the surgical wards. Conclusion: Smoking prevalence was higher in hospitalised patients than in the local general population. Many inpatients were not interested in quitting; however, a third had significant nicotine withdrawal symptoms. All inpatients who are active smokers should be identified and given universal brief smoking cessation advice. Patients with severe withdrawal symptoms should be allowed to smoke outside, and nicotine withdrawal pharmacotherapy should be provided to those who are bedbound or express a desire to stop smoking during the current admission. Study synopsis: What the study adds. A single data point prevalence study of active smokers at Groote Schuur Hospital, Cape Town, was conducted. The prevalence of smoking was higher in the hospitalised patients than in the general community, but not all smokers were identified by the clinicians. Although symptoms of nicotine withdrawal were severe in some patients, motivation to quit smoking was not related to the degree of withdrawal being experienced. Many patients were not motivated to quit smoking.Implications of the findings. Better identification of inpatient smokers is required, and all should be given smoking cessation advice. Withdrawal symptoms can be severe in some patients, and those who are not interested in stopping smoking should allowed to smoke outside or be provided with nicotine withdrawal pharmacotherapy while in hospital. Those who are willing to quit should be supported as well as possible, including provision of nicotine replacement therapy or varenicline, and followed up after discharge as best practice.
ABSTRACT
INTRODUCTION: Microscopically positive resection margins (R1) are associated with poorer outcomes in patients with colorectal cancer. However, different definitions of R1 margins exist. It is unclear to what extent the definitions used in everyday clinical practice differ within and between nations. This study sought to investigate variations in the definition of R1 margins in colorectal cancer and the importance of margin status in clinical decision-making. MATERIALS AND METHODS: A 14-point survey was developed by members of The European Society of Surgical Oncology (ESSO) Youngs Surgeons and Alumni Club (EYSAC) Research Academy targeting all members of the multidisciplinary team (MDT) treating patients with colorectal cancer. The survey was distributed on social media, in ESSO's monthly newsletter and via national societies. RESULTS: In total, 137 responses were received. Most respondents were from Europe (89.7%), with the majority from Denmark (56.9%). Less than 2/3 of respondents defined R1 margins as the presence of viable cancer cells ≤1 mm of the margin. Only 60% reported that subdivisions of R1 margins (primary tumour vs tumour deposit vs metastatic lymph node) are routinely available. More than 20% of respondents reported that pathology reports are not routinely reviewed at MDT meetings. Less than half of respondents considered margin status in decision-making for type and duration of adjuvant chemotherapy in Stage III colon cancer. CONCLUSION: The definitions and perceived clinical importance of microscopically positive margins in patients with colorectal cancer appear to vary. Adoption of an international dataset for pathology reporting may help to standardise current practices.
Subject(s)
Colonic Neoplasms , Surgical Oncology , Humans , Margins of Excision , Surveys and Questionnaires , Europe , Retrospective StudiesABSTRACT
A thermodynamic analysis is performed for an aero derivative gas turbine engine which utilizes steam injection to increase its efficiency. The target was to explore the performance of a high efficiency gas turbine unit for electric power generation without downstream Rankine cycle. A Rankine cycle for exhaust heat recovery is unattractive because of its large response time and cost of investment. The main purpose of this research was to develop a better understanding of how the optimal cycle efficiency is reached, when the steam for injection is generated by use of the turbine exhaust heat. The STIG cycle becomes attractive for grid stabilization because of its low CAPEX and small footprint and response time. A thermodynamic model has been developed to simulate the simple cycle gas turbine, steam generation and effects of steam injection. Reference input parameters for the model are taken for the GE LM6000 turbine as publicly available. The performance of the engine without steam injection as predicted by the model is compared with literature for validation and compares well. The performance of the STIG cycle as a function of operation parameter steam mass flow and design parameters pressure ratio and turbine inlet temperature is investigated and the optimal parameter settings determined. It is found that this type of cycle shows a very specific parameter setting for optimal efficiency. By using steam injection for the chosen turbine and its parameters an efficiency gain of around 11% points and an output power augmentation of 45% can be achieved.
ABSTRACT
Enteroviruses (EV) commonly cause hand, foot and mouth disease (HFMD), and can also cause potentially fatal neurological and systemic complications. In our laboratory, sequencing 5' untranslated region (UTR) of the viral genome has been the routine method of genotyping EVs. During a recent localised outbreak of aseptic meningitis, sequencing the 5'UTR identified the causative virus as EV-A71, which did not fit with the clinical syndrome or illness severity. When genotyped using a different target gene, VP1, the result was different. This led us to evaluate the accuracy of the two different target genome regions and compare them against whole genome sequencing (WGS). We aimed to optimise the algorithm for detection and characterisation of EVs in the diagnostic laboratory. We hypothesised that VP1 and WGS genotyping would provide different results than 5'UTR in a subset of samples. Clinical samples from around New South Wales which were positive for EV by commercial polymerase chain reaction (PCR) assays were genotyped by targeting three different viral genome regions: the 5'UTR, VP1 and WGS. Sequencing was performed by Sanger and next generation sequencing. The subtyping results were compared. Of the 74/118 (63%) samples that were successfully typed using both the 5'UTR and the VP1 method, the EV typing result was identical for 46/74 (62%) samples compared to WGS as the gold standard. The same EV group but different EV types were found in 22/74 (30%) samples, and 6/74 (8%) samples belonged to different EV groups depending on typing method used. Genotyping with WGS and VP1 is more accurate than 5'UTR. Genotyping by the 5'UTR method is very sensitive, but less specific.
Subject(s)
Enterovirus Infections , Enterovirus , 5' Untranslated Regions/genetics , Enterovirus/genetics , Enterovirus Infections/diagnosis , Humans , Molecular Typing , Whole Genome SequencingABSTRACT
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) genomic surveillance has been vital in understanding the spread of coronavirus disease 2019 (COVID-19), the emergence of viral escape mutants, and variants of concern. However, low viral loads in clinical specimens affect variant calling for phylogenetic analyses and detection of low-frequency variants, important in uncovering infection transmission chains. We systematically evaluated three widely adopted SARS-CoV-2 whole-genome sequencing methods for their sensitivity, specificity, and ability to reliably detect low-frequency variants. Our analyses reveal that the ARTIC v3 protocol consistently displays high sensitivity for generating complete genomes at low viral loads compared with the probe-based Illumina Respiratory Viral Oligo panel and a pooled long-amplicon method. We show substantial variability in the number and location of low-frequency variants detected using the three methods, highlighting the importance of selecting appropriate methods to obtain high-quality sequence data from low-viral-load samples for public health and genomic surveillance purposes.
Subject(s)
COVID-19 , SARS-CoV-2 , Base Sequence , Genome, Viral , Humans , Phylogeny , Whole Genome SequencingABSTRACT
Studies investigating neighborhood walkability and physical activity in people with type 2 diabetes (T2D) mainly used self-report measures, and only few studies assessed the association with glycemic control. This study assessed the associations between objectively measured (i.e. GIS based) and subjectively measured (i.e. questionnaire-based) neighborhood walkability and changes in glycemic markers in people with T2D, and whether this association was mediated by device-measured physical activity (PA), in the Diabetes Care System Cohort (n = 1230). Neither objective or subjectively measured walkability was associated with glycemic control. In mediation analyses we observed no overall mediation by PA.
Subject(s)
Diabetes Mellitus, Type 2 , Environment Design , Exercise , Humans , Residence Characteristics , WalkingABSTRACT
The first laboratory confirmed case of Coronavirus disease 2019 (COVID-19) in Australia was in Victoria on 25 January 2020 in a man returning from Wuhan city, Hubei province, the People's Republic of China. This was followed by three cases in New South Wales the following day. The Australian Government activated the Australian Health Sector Emergency Response Plan for Novel Coronavirus on 27 February 2020 in anticipation of a pandemic. Subsequently, the World Health Organization declared COVID-19 to be a Public Health Emergency of International Concern followed by a pandemic on 30 January 2020 and 11 March 2020, respectively. Laboratory testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, is key in identifying infected persons to guide timely public health actions of contact tracing and patient isolation to limit transmission of infection. This article aims to provide a comprehensive overview of current laboratory diagnostic methods for SARS-CoV-2, including nucleic acid testing, serology, rapid antigen detection and antibody tests, virus isolation and whole genome sequencing. The relative advantages and disadvantages of the different diagnostic tests are presented, as well as their value in different clinical, infection control and public health contexts. We also describe the challenges in the provision of SARS-CoV-2 diagnostics in Australia, a country with a relatively low COVID-19 incidence in the first pandemic wave but in which prevalence could rapidly change.
Subject(s)
COVID-19 Testing/methods , COVID-19/diagnosis , SARS-CoV-2/isolation & purification , Australia , Clinical Laboratory Techniques/methods , HumansABSTRACT
INTRODUCTION: There is limited data on the analytical performance of commercial nucleic acid tests (NATs) for laboratory confirmation of COVID-19 infection. METHODS: Nasopharyngeal, combined nose and throat swabs, nasopharyngeal aspirates and sputum was collected from persons with suspected SARS-CoV-2 infection, serial dilutions of SARS-CoV-2 viral cultures and synthetic positive controls (gBlocks, Integrated DNA Technologies) were tested using i) AusDiagnostics assay (AusDiagnostics Pty Ltd); ii) in-house developed assays targeting the E and RdRp genes; iii) multiplex PCR assay targeting endemic respiratory viruses. Discrepant SARS-CoV-2 results were resolved by testing the N, ORF1b, ORF1ab and M genes. RESULTS: Of 52 clinical samples collected from 50 persons tested, respiratory viruses were detected in 22 samples (42 %), including SARS CoV-2 (nâ¯=â¯5), rhinovirus (nâ¯=â¯7), enterovirus (nâ¯=â¯5), influenza B (nâ¯=â¯4), hMPV (nâ¯=â¯5), influenza A (nâ¯=â¯2), PIV-2 (nâ¯=â¯1), RSV (nâ¯=â¯2), CoV-NL63 (nâ¯=â¯1) and CoV-229E (nâ¯=â¯1). SARS-CoV-2 was detected in four additional samples by the AusDiagnostics assay. Using the in-house assays as the "gold standard", the sensitivity, specificity, positive and negative predictive values of the AusDiagnostics assay was 100 %, 92.16 %, 55.56 % and 100 % respectively. The Ct values of the real-time in-house-developed PCR assay targeting the E gene was significantly lower than the corresponding RdRp gene assay when applied to clinical samples, viral culture and positive controls (mean 21.75 vs 28.1, pâ¯=â¯0.0031). CONCLUSIONS: The AusDiagnostics assay is not specific for the detection SARS-CoV-2. Any positive results should be confirmed using another NAT or sequencing. The case definition used to investigate persons with suspected COVID-19 infection is not specific.
Subject(s)
Betacoronavirus/isolation & purification , Coronavirus Infections/diagnosis , Molecular Diagnostic Techniques/methods , Nasopharynx/virology , Pneumonia, Viral/diagnosis , Adolescent , Adult , Aged , Aged, 80 and over , COVID-19 , Child , Child, Preschool , Female , Humans , Infant , Infant, Newborn , Male , Middle Aged , Pandemics , SARS-CoV-2 , Sensitivity and Specificity , Young AdultABSTRACT
AIMS: The application of essential oils (EOs) and their components as food preservatives is promising but requires a deeper understanding of their mechanisms of action. This study aims to evaluate the effects of thyme EO, carvacrol, citral and 2-(E)-hexenal, on whole-genome gene expression (the transcriptome), as well as the fatty acid (FA) composition of the cell membranes of Escherichia coli K12. METHODS AND RESULTS: Therefore, we studied the response against 1 h of exposure to sublethal concentrations of natural antimicrobials, of exponentially growing E. coli K12, using DNA microarray technology and a gas chromatographic method. The results show that treatment with a sublethal concentration of the antimicrobials strongly affects global gene expression in E. coli for all antimicrobials used. Major changes in the expression of genes involved in metabolic pathways as well as in FA biosynthesis and protection against oxidative stress were evidenced. Moreover, the sublethal treatments resulted in increased levels of unsaturated and cyclic FAs as well as an increase in the chain length compared to the controls. CONCLUSIONS: The down-regulation of genes involved in aerobic metabolism indicates a shift from respiration to fermentative growth. Moreover, the results obtained suggest that the cytoplasmic membrane of E. coli is the major cellular target of EOs and their components. In addition, the key role of membrane unsaturated FAs in the response mechanisms of E. coli to natural antimicrobials has been confirmed in this study. SIGNIFICANCE AND IMPACT OF THE STUDY: The transcriptomic data obtained signify a further step to understand the mechanisms of action of natural antimicrobials also when sublethal concentrations and short-term exposure. In addition, this research goes in deep correlating the transcriptomic modification with the changes in E. coli FA composition of cell membrane identified as the main target of the natural antimicrobials.
Subject(s)
Aldehydes , Escherichia coli , Monoterpenes , Oils, Volatile , Thymus Plant , Transcriptome/drug effects , Acyclic Monoterpenes , Aldehydes/chemistry , Aldehydes/pharmacology , Cell Membrane/chemistry , Cell Membrane/drug effects , Cymenes , Escherichia coli/cytology , Escherichia coli/drug effects , Escherichia coli/genetics , Escherichia coli/metabolism , Fatty Acids/analysis , Gene Expression Profiling , Monoterpenes/chemistry , Monoterpenes/pharmacology , Oils, Volatile/chemistry , Oils, Volatile/pharmacology , Phytochemicals/chemistry , Phytochemicals/pharmacologyABSTRACT
A generic formalism is proposed for reference dosimetry in the presence of a magnetic field. Besides the regular correction factors from the conventional reference dosimetry formalisms, two factors are used to take into account magnetic field effects: (1) a dose conversion factor to correct for the change in local dose distribution and (2) a correction of the reading of the dosimeter used for the reference dosimetry measurements. The formalism was applied to the Elekta MRI-Linac, for which the 1.5 T magnetic field is orthogonal to the 7 MV photon beam. For this setup at reference conditions it was shown that the dose decreases with increasing magnetic field strength. The reduction in local dose for a 1.5 T transverse field, compared to no field is 0.51% ± 0.03% at the reference point of 10 cm depth. The effect of the magnetic field on the reading of the dosimeter was measured for two waterproof ionization chambers types (PTW 30013 and IBA FC65-G) before and after multiple ramp-up and ramp-downs of the magnetic field. The chambers were aligned perpendicular and parallel to the magnetic field. The corrections of the readings of the perpendicularly aligned chambers were 0.967 ± 0.002 and 0.957 ± 0.002 for respectively the PTW and IBA ionization chambers. In the parallel alignment the corrections were small; 0.997 ± 0.001 and 1.002 ± 0.003 for the PTW and IBA chamber respectively. The change in reading due to the magnetic field can be measured by individual departments. The proposed formalism can be used to determine the correction factors needed to establish the absorbed dose in a magnetic field. It requires Monte Carlo simulations of the local dose and measurements of the response of the dosimeter. The formalism was successfully implemented for the MRI-Linac and is applicable for other field strengths and geometries.
Subject(s)
Magnetic Fields , Photons , Radiation Dosimeters/standards , Humans , Monte Carlo Method , Radiometry/standards , Reference StandardsABSTRACT
The transverse magnetic field of an MRI-linac sweeps contaminant electrons away from the radiation beam. Films oriented perpendicular to the magnetic field and 5 cm from the radiation beam edge show a projection of the divergent beam, indicating that contaminant electrons spiral along magnetic field lines and deposit dose on surfaces outside the primary beam perpendicular to the magnetic field. These spiraling contaminant electrons (SCE) could increase skin doses to protruding regions of the patient along the cranio-caudal axis. This study investigated doses from SCE for an MRI-linac comprising a 7 MV linac and a 1.5 T MRI scanner. Surface doses to films perpendicular to the magnetic field and 5 cm from the radiation beam edge showed increased dose within the projection of the primary beam, whereas films parallel to the magnetic field and 5 cm from the beam edge showed no region of increased dose. However, the dose from contaminant electrons is absorbed within a few millimeters. For large fields, the SCE dose is within the same order of magnitude as doses from scattered and leakage photons. Doses for both SCE and scattered photons decrease rapidly with decreasing beam size and increasing distance from the beam edge.
Subject(s)
Electrons , Magnetic Fields , Magnetic Resonance Imaging/methods , Photons , Skin/radiation effects , Humans , Particle AcceleratorsABSTRACT
As a prerequisite for clinical treatments it was necessary to characterize the Elekta 1.5 T MRI-linac 7 MV FFF radiation beam. Following acceptance testing, beam characterization data were acquired with Semiflex 3D (PTW 31021), microDiamond (PTW 60019), and Farmer-type (PTW 30013 and IBA FC65-G) detectors in an Elekta 3D scanning water phantom and a PTW 1D water phantom. EBT3 Gafchromic film and ion chamber measurements in a buildup cap were also used. Special consideration was given to scan offsets, detector effective points of measurement and avoiding air gaps. Machine performance has been verified and the system satisfied the relevant beam requirements of IEC60976. Beam data were acquired for field sizes between 1 × 1 and 57 × 22 cm2. New techniques were developed to measure percentage depth dose (PDD) curves including the electron return effect at beam exit, which exhibits an electron-type practical range of 1.2 ± 0.1 cm. The Lorentz force acting on the secondary charged particles creates an asymmetry in the crossline profiles with an average shift of +0.24 cm. For a 10 × 10 cm2 beam, scatter from the cryostat contributes 1% of the dose at isocentre. This affects the relative output factors, scatter factors and beam profiles, both in-field and out-of-field. The average 20%-80% penumbral width measured for small fields with a microDiamond detector at 10 cm depth is 0.50 cm. MRI-linac penumbral widths are very similar to that of the Elekta Agility linac MLC, as is the near-surface dose PDD(0.2 cm) = 57%. The entrance surface dose is â¼36% of Dmax. Cryostat transmission is quantified for inclusion within the treatment planning system. As a result, the 1.5 T MRI-linac 7 MV FFF beam has been characterised for the first time and is suitable for clinical use. This was a key step towards the first clinical treatments with the MRI-linac, which were delivered at University Medical Center Utrecht in May 2017 (Raaymakers et al 2017 Phys. Med. Biol. 62 L41-50).
Subject(s)
Magnetic Resonance Imaging/methods , Particle Accelerators , Phantoms, Imaging , Radiometry/methods , Electrons , Humans , Magnetic Fields , Patient Positioning , WaterABSTRACT
Knowledge concerning the normal aging of cerebral white matter will improve our understanding of abnormal changes in neurodegenerative diseases. The microstructural basis of white matter maturation and aging can be investigated using diffusion tensor imaging (DTI). Generally, diffusion anisotropy increases during childhood and adolescence followed by a decline in middle age. However, this process is subject to spatial variations between tracts. The aim of this study was to investigate to what extent age-related variations also occur within tracts. DTI parameters were compared between segments of two white matter tracts, the cingulate bundle (CB) and the inferior fronto-occipital fasciculus (IFO), in 257 healthy individuals between 13 and 84years of age. Segments of the CB and the IFO were extracted and parameters for each segment were averaged across the hemispheres. The data was analysed as a function of age. Results show that age-related changes differ both between and within individual tracts. Different age trajectories were observed in all segments of the analysed tracts for all DTI parameters. In conclusion, aging does not affect white matter tracts uniformly but is regionally specific; both between and within white matter tracts.
Subject(s)
Aging/physiology , Diffusion Magnetic Resonance Imaging/methods , Diffusion Tensor Imaging/methods , White Matter/diagnostic imaging , White Matter/physiopathology , Adolescent , Adult , Aged , Aged, 80 and over , Female , Humans , Male , Middle Aged , Young AdultABSTRACT
Accurate small-field dosimetry is critical for a magnetic resonance linac (MRI-linac). The PTW 60019 microDiamond is close to an ideal detector for small field dosimetry due to its small physical size, high signal-to-noise ratio and approximate water equivalence. It is important to fully characterise the performance of the detector in a 1.5 T magnetic field prior to its use for MRI-linac commissioning and quality assurance. Standard techniques of detector testing have been implemented, or adapted where necessary to suit the capabilities of the MRI-linac. Detector warmup, constancy, dose linearity, dose rate linearity, field size dependence and leakage were within tolerance. Measurements with the detector were consistent with ion chamber measurements for medium sized fields. The effective point of measurement of the detector when used within a 1.5 T magnetic field was determined to be 0.80 ± 0.23 mm below the top surface of the device, consistent with the existing vendor recommendation and alignment mark at 1.0 mm. The angular dependence was assessed. Variations of up to 9.7% were observed, which are significantly greater than in a 0 T environment. Within the expected range of use, the maximum effect is approximately 0.6% which is within tolerance. However for large beams within a magnetic field, the divergence and consequent variation in angle of photon incidence means that the microDiamond would not be ideal for characterising the profiles and it would not be suitable for determining large-field beam parameters such as symmetry. It would also require a correction factor prior to use for patient-specific QA measurements where radiation is delivered from different gantry angles. The results of this study demonstrate that the PTW 60019 microDiamond detector is suitable for measuring small radiation fields within a 1.5 T magnetic field and thus is suitable for use in MRI-linac commissioning and quality assurance.
Subject(s)
Magnetic Resonance Imaging/methods , Particle Accelerators/instrumentation , Phantoms, Imaging , Radiometry/instrumentation , Humans , Magnetic Fields , Photons , Radiometry/methods , WaterABSTRACT
The integration of 1.5 T MRI functionality with a radiotherapy linear accelerator (linac) has been pursued since 1999 by the UMC Utrecht in close collaboration with Elekta and Philips. The idea behind this integrated device is to offer unrivalled, online and real-time, soft-tissue visualization of the tumour and the surroundings for more precise radiation delivery. The proof of concept of this device was given in 2009 by demonstrating simultaneous irradiation and MR imaging on phantoms, since then the device has been further developed and commercialized by Elekta. The aim of this work is to demonstrate the clinical feasibility of online, high-precision, high-field MRI guidance of radiotherapy using the first clinical prototype MRI-Linac. Four patients with lumbar spine bone metastases were treated with a 3 or 5 beam step-and-shoot IMRT plan. The IMRT plan was created while the patient was on the treatment table and based on the online 1.5 T MR images; pre-treatment CT was deformably registered to the online MRI to obtain Hounsfield values. Bone metastases were chosen as the first site as these tumors can be clearly visualized on MRI and the surrounding spine bone can be detected on the integrated portal imager. This way the portal images served as an independent verification of the MRI based guidance to quantify the geometric precision of radiation delivery. Dosimetric accuracy was assessed post-treatment from phantom measurements with an ionization chamber and film. Absolute doses were found to be highly accurate, with deviations ranging from 0.0% to 1.7% in the isocenter. The geometrical, MRI based targeting as confirmed using portal images was better than 0.5 mm, ranging from 0.2 mm to 0.4 mm. In conclusion, high precision, high-field, 1.5 T MRI guided radiotherapy is clinically feasible.
Subject(s)
Bone Neoplasms/radiotherapy , Lumbosacral Region/radiation effects , Magnetic Resonance Imaging/instrumentation , Particle Accelerators/instrumentation , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Image-Guided/methods , Spinal Neoplasms/radiotherapy , Aged , Bone Neoplasms/secondary , Humans , Middle Aged , Phantoms, Imaging , Radiometry , Radiotherapy Dosage , Spinal Neoplasms/pathologyABSTRACT
PURPOSE: A protocol for reference dosimetry for the MR-linac is under development. The 1.5 T magnetic field changes the mean path length of electrons in an air-filled ionization chamber but has little effect on the electron trajectories in a surrounding phantom. It is therefore necessary to correct the response of an ionization chamber for the influence of the magnetic field. Solid phantoms are used for dosimetry measurements on the MR-linac, but air is present between the chamber wall and phantom insert. This study aimed to determine if this air influences the ion chamber measurements on the MR-linac. The absolute response of the chamber and reproducibility of dosimetry measurements were assessed on an MR-linac in solid and water phantoms. The sensitivity of the chamber response to the distribution of air around the chamber was also investigated. METHODS: Measurements were performed on an MR-linac and replicated on a conventional linac for five chambers. The response of three waterproof chambers was measured with air and with water between the chamber and the insert to measure the influence of the air volume on absolute chamber response. The distribution of air around the chamber was varied indirectly by rotating each chamber about the longitudinal chamber axis in a solid phantom and a water phantom (waterproof chambers only) and measuring the angular dependence of the chamber response, and varied directly by displacing the chamber in the phantom insert using a paper shim positioned at different orientations between the chamber casing and the insert. RESULTS: The responses of the three waterproof chambers measured on the MR-linac were 0.7%-1.2% higher with water than air in the chamber insert. The responses of the chambers on the conventional linac changed by less than 0.3% when air in the insert was replaced with water. The angular dependence of the chambers ranged from 0.6% to 1.9% in the solid phantom on the MR-linac but was less than 0.5% in water on the MR-linac and less than 0.3% in the solid phantom on the conventional linac. Inserting a shim around the chamber induced changes of the chamber response in a magnetic field of up to 2.2%, but the change in chamber response on the conventional linac was less than 0.3%. CONCLUSIONS: The interaction between the magnetic field and secondary electrons in the air around the chamber reduces the charge collected from 0.7% to 1.2%. The large angular dependence of ion chambers measured in the plastic phantom in a magnetic field appears to arise from a change of air distribution as the chamber is moved within the insert, rather than an intrinsic isotropy of the chamber sensitivity to radiation. It is recommended that reference dosimetry measurements on the MR-linac can be performed only in water, rather than in existing plastic phantoms.
Subject(s)
Air , Magnetic Resonance Imaging/instrumentation , Particle Accelerators/instrumentation , Phantoms, Imaging , Radiometry/instrumentation , Radiometry/methods , Equipment Design , Magnetic Resonance Imaging/methods , Radiotherapy, Image-Guided/instrumentation , Radiotherapy, Image-Guided/methods , WaterABSTRACT
AIM: Various early intervention programmes have been developed in response to the high rate of neurodevelopmental problems in very preterm infants. We investigated longitudinal effects of the Infant Behavioral Assessment and Intervention Program on cognitive and motor development of very preterm infants at the corrected ages of six months to five and a half years. METHODS: This randomised controlled trial divided 176 infants with a gestational age <32 weeks or birthweight <1500 g into intervention (n = 86) and control (n = 90) groups. Cognitive development and motor development were assessed with the Bayley Scales of Infant Development at the CAs of six, 12 and 24 months and at five and a half years with the Wechsler Preschool and Primary Scale of Intelligence and the Movement Assessment Battery for Children. RESULTS: We found significant longitudinal intervention effects (0.4 SD, p = 0.006) on motor development, but no significant impact on cognitive development (p = 0.063). Infants with bronchopulmonary dysplasia showed significant longitudinal intervention effects for cognitive (0.7 SD; p = 0.019) and motor (0.9 SD; p = 0.026) outcomes. Maternal education had little effect on intervention effects over time. CONCLUSION: The Infant Behavioral Assessment and Intervention Program led to long-term developmental improvements in the intervention group, especially in infants with BPD.
Subject(s)
Infant, Premature/growth & development , Infant, Very Low Birth Weight/growth & development , Neurodevelopmental Disorders/prevention & control , Bronchopulmonary Dysplasia/complications , Cognition , Educational Status , Female , Humans , Infant , Infant, Newborn , Male , Motor Skills , Neurodevelopmental Disorders/etiologyABSTRACT
At the UMC Utrecht, a linear accelerator with integrated magnetic resonance imaging (MRI) has been developed, the MR-linac. Patient-specific quality assurance (QA) of treatment plans for MRI-based image guided radiotherapy requires QA equipment compatible with this 1.5 T magnetic field. The purpose of this study was to examine the performance characteristics of the ArcCHECK-MR in a transverse 1.5 T magnetic field. To this end, the short-term reproducibility, dose linearity, dose rate dependence, field size dependence, dose per pulse dependence and inter-diode dose response variation of the ArcCHECK-MR diode array were evaluated on a conventional linac and on the MR-linac. The ArcCHECK-MR diode array performed well for all tests on both linacs, no significant differences in performance characteristics were observed. Differences in the maximum dose deviations between both linacs were less than 1.5%. Therefore, we conclude that the ArcCHECK-MR can be used in a transverse 1.5 T magnetic field.