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| 2. |
- Ceberg, Crister, et al.
(author)
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Prediction of stopping-power ratios in flattening-filter free beams.
- 2010
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In: Medical Physics. - : Wiley. - 0094-2405. ; 37:3, s. 1164-1168
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Journal article (peer-reviewed)abstract
- PURPOSE: In recent years, there has been an increasing interest in flattening-filter free (FFF) beams. However, since the removal of the flattening filter will affect both the mean and the variance of the energy spectrum, current beam-quality specifiers may not be adequate for reference dosimetry in such beams. The purpose of this work was to investigate an alternative, more general beam-quality specifier. METHODS: The beam-quality specifier used in this work was a combination of the kerma-weighted mean and the coefficient of variation of the linear attenuation coefficient in water. These parameters can in theory be determined from narrow-beam transmission measurements using a miniphantom "in-air," which is a measurement condition well suited also to small and nonstandard fields. The relation between the Spencer-Attix stopping-power ratios and this novel beam-quality specifier was described by a simple polynomial. For reference, the authors used Monte Carlo calculated spectra and stopping-power data for nine different beams, with and without flattening filter. RESULTS: The polynomial coefficients were obtained by least-squares optimization. For all beams included in this investigation, the average of the differences between the predicted and the Monte Carlo calculated stopping-power ratios was 0.02 +/- 0.17% (1 SD) (including TomoTherapy and CyberKnife example beams). CONCLUSIONS: An alternative dual-parameter beam-quality specifier was investigated. The evaluation suggests that it can be used successfully to predict stopping-power ratios in FFF as well as conventional beams, regardless of filtration.
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| 4. |
- Jakobsson, Eva, 1960, et al.
(author)
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End-of-life in a Swedish population: demographics, social conditions and characteristics of places of death.
- 2006
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In: Scandinavian journal of caring sciences. - : Wiley. - 0283-9318 .- 1471-6712. ; 20:1, s. 10-7
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Journal article (peer-reviewed)abstract
- The objectives of this study were to identify and describe the demographics and social conditions as well as characteristics of the places of death in a randomly selected sample that died in a county in Sweden during 2001. The present study reports part of the findings from a larger study undertaken during 2003 using a survey design of retrospective reviews of death certificates, medical records, and nursing records. Among several noteworthy findings are: first, an examination of these individuals' living arrangements reveal not only a large and vulnerable group that lives alone at the end-of-life but also a group living separated from their partners near end-of-life; second, individuals differ with respect to residence prior to death, that is private homes versus residential care facilities, imparting highly different contexts of care at the end-of-life; and third, a high prevalence of institutionalized deaths demonstrates that places of death other than hospitals and residential care facilities are uncommon, if not rare. It is concluded that increased attention to the social circumstances of the time period surrounding individuals' at the end-of-life is essential. There is need to develop more integrated models of care for dying people. Contemporary services available are not designed to meet a wide range of peoples' needs at the end-of-life. Home-based care, residential care and hospital care must be adapted to the changing patterns of dying. The services available should be organized to the benefit of the users rather than around the providers. This is the first study of its kind of a Swedish sample and while the data are limited to one county in Sweden its findings may contribute to a deeper understanding of demographic and social patterns at the end-of-life in general.
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| 5. |
- Johnsson, Stefan, et al.
(author)
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On beam quality and stopping power ratios for high-energy x-rays
- 2000
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In: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 45:10, s. 2733-2745
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Journal article (peer-reviewed)abstract
- The aim of this work is to quantitatively compare two commonly used beam quality indices, IPR(20/10) and %dd(10)x, with respect to their ability to predict stopping power ratios (water to air), s(w,air), for high-energy x-rays. In particular, effects due to a varied amount of filtration of the photon beam will be studied. A new method for characterizing beam quality is also presented, where the information we strive to obtain is the moments of the spectral distribution. We will show how the moments enter into a general description of the transmission curve and that it is possible to correlate the moments to s(w,air) with a unique and simple relationship. Comparisons with TPR(20/10) and %dd(10), show that the moments are well suited for beam quality specification in terms of choosing the correct s(w,air).
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| 6. |
- Johnsson, Stefan, et al.
(author)
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Transmission measurements in air using the ESTRO mini-phantom
- 1999
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In: Physics in Medicine and Biology. - 1361-6560. ; 44:10, s. 2445-2450
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Journal article (peer-reviewed)abstract
- The aim of this work is to study the possibility of using the ESTRO mini-phantom for transmission measurements of primary kerma in water at a point free in air. We discuss in-air measurements in general, with special attention given to in-air equivalent measurements using a water equivalent mini-phantom. The study includes four different photon energies (4, 6, 10 and 18 MV), where scoring of dose and primary kerma inside a mini-phantom in narrow beam geometry is performed with the Monte Carlo code EGS4. The results reveal that relative measurements (i.e. with and without a water absorber present) at 10 cm depth in a mini-phantom do not represent the variation of primary kerma in water at a point free in air (deviations as large as 7% at 4 MV are observed). Minimum deviations are obtained at depths somewhat larger than the depth of dose maximum. The observed deviations are due to a considerable beam hardening in the water absorber, which changes the amount of attenuation and scatter inside the mini-phantom.
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| 7. |
- Knöös, Tommy, et al.
(author)
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Independent checking of the delivered dose for high-energy X-rays using a hand-held PC
- 2001
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In: Radiotherapy and Oncology. - 1879-0887. ; 58:2, s. 201-208
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Journal article (peer-reviewed)abstract
- Background and purpose: The requirements on the delivered dose in radical radiation therapy are extremely high. The dose should be within a few percent and also delivered with high accuracy in space. Vendors and users have successfully managed to implement radiation therapy systems, which are able to achieve these demands with high accuracy and reproducibility. These systems include computerized tomography scanners, treatment planning systems, simulators, treatment machines, and record and verify systems. More and more common are also computer networks to assure data integrity when transferring information between the systems. Even if these systems are commissioned and kept under quality assurance programs to maintain their accuracy, errors may be introduced. Especially, the human factor is an uncontrolled parameter that may introduce errors. Thus, unintentional changes or incorrect handling of data may occur during clinical use of the equipment. Having an independent dose calculation system implemented in the daily quality assurance process may assure a high quality of treatments and avoidance of severe errors.Materials and methods: To accomplish this, a system of equations for calculating the absorbed dose to the prescription point from the set-up information, has been compiled into a dose-calculation engine. The model is based on data completely independent of the treatment planning system (TPS). The fundamental parameter in the dose engine is the linear attenuation coefficient for the primary photons. This parameter can readily be determined experimentally. The dose calculation engine has been programmed into a hand-held PC allowing direct calculation of the dose to the prescription point when the first treatment is delivered to the patient.Results and conclusion: The model is validated with measurements and is shown to be within +/-1.0% (1 SD). Comparison against a state-of-the-art TPS shows an average difference of 0.3% with a standard deviation of +/-2.1%. An action level covering 95% of the cases has been chosen, i.e. +/-4.0%. Deviations larger than this are with a high probability due to erroneous handling of the patient set-up data. This system has been implemented into the daily clinical quality control program.
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| 8. |
- Swedberg, Yngve, et al.
(author)
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On longitudinal caries index data. A comparison study between cohort and cross-sectional attempts.
- 1997
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In: Swedish dental journal. - 0347-9994. ; 21:5, s. 205-11
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Journal article (peer-reviewed)abstract
- The aim of the present study was to compare registered data of caries prevalence and incidence from cross-sectional studies of specified age groups with the corresponding caries data from cohorts of individuals receiving dental health service from the same dental clinic during the years studied. The study covered two 15-19-year groups, who had been offered complete dental care from three years of age in the City of Göteborg for the time periods 1986/7-1990/1. When compared, the longitudinal cohort attempts often gave statistically significant different values to those of the cross-sectional year classes, which should be considered when presenting caries index mean values in dental health reviews. It is not indifferent to choose between longitudinal cohort and cross-sectional year class attempts when searching for dental health treatment effects. Due to the advantages of using longitudinal cohort study methods, and with regard to the differences of the study design used, as pointed out in the study, the use of longitudinal cohort patient material, extracted from cross-sectional epidemiological data bases, could favour analysis of the effects of different preventive dental care programs.
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| 9. |
- Vandoolaeghe, Pauline, et al.
(author)
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Interaction between Lamellar (Vesicles) and Nonlamellar Lipid Liquid-Crystalline Nanoparticles as Studied by Time-Resolved Small-Angle X-ray Diffraction
- 2009
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:7, s. 3999-4008
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Journal article (peer-reviewed)abstract
- The kinetics of structure change when dispersions of two different types of lipid-based liquid-crystalline phases, one lamellar and one reversed, are mixed has been investigated using synchrotron small-angle X-ray diffraction and ellipsometry. The systems studied were (i) cubic-phase nanoparticles (CPNPs) based on glycerol monooleate (GMO) stabilized with a nonionic block copolymer, Pluronic F-127; (ii) CPNPs based on phytantriol (PtOH) stabilized with D-alpha-Tocopheryl polyethylene glycol 1000 succinate (Vitamin E TPGS); and (iii) hexagonal-phase nanoparticles (HPNPs) based on a lipid mixture of diglycerol monooleate/glycerol dioleate, stabilized by Pluronic F-127. Time-resolved small-angle X-ray diffraction was used to track structural changes within nonlamellar nanoparticles when they interact with uni- and multilamellar vesicles of dioleoylphosphatidylcholine and dipalmitoylphatidylcholine. The results are very dependent on the type of nanoparticles under investigation. For GMO-based CPNPs, a strong interaction is observed on mixing with vesicular dispersions that leads to large changes in unit size dimensions as well as a later transition from cubic to lamellar structure. These results are in good agreement with previous studies on the interaction of GMO-based CPNPs with planar bilayers using neutron reflectivity, where the diffraction peak shifted with time upon mixing. The structural changes are much less prominent for the PtOH-based CPNPs and the HPNPs upon mixing with phospholipid vesicles. These results are correlated with those from measurement studying interactions between the liquid-crystalline nanoparticles and supported phospholipid bilayers by ellipsometry. Also, here the GMO-based CPNPs show more pronounced and rapid adsorption and interaction with the supported bilayer surface than do the other types of nonlamellar nanoparticles. The interaction also depends on the bilayer properties, where significantly slower lipid mixing is observed for a bilayer in the gel state compared to a bilayer in the liquid-crystalline phase. This study is not only relevant for drug-delivery applications but also shows the potential of synchrotron small-angle X-ray diffraction in studying time-dependent structural changes as a consequence of the interaction between different lipid self-assembled aggregates in complex systems.
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| 11. |
- Åberg, Maria A I, 1972, et al.
(author)
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Cardiovascular fitness is associated with cognition in young adulthood.
- 2009
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490.
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Journal article (peer-reviewed)abstract
- During early adulthood, a phase in which the central nervous system displays considerable plasticity and in which important cognitive traits are shaped, the effects of exercise on cognition remain poorly understood. We performed a cohort study of all Swedish men born in 1950 through 1976 who were enlisted for military service at age 18 (N = 1,221,727). Of these, 268,496 were full-sibling pairs, 3,147 twin pairs, and 1,432 monozygotic twin pairs. Physical fitness and intelligence performance data were collected during conscription examinations and linked with other national databases for information on school achievement, socioeconomic status, and sibship. Relationships between cardiovascular fitness and intelligence at age 18 were evaluated by linear models in the total cohort and in subgroups of full-sibling pairs and twin pairs. Cardiovascular fitness, as measured by ergometer cycling, positively associated with intelligence after adjusting for relevant confounders (regression coefficient b = 0.172; 95% CI, 0.168-0.176). Similar results were obtained within monozygotic twin pairs. In contrast, muscle strength was not associated with cognitive performance. Cross-twin cross-trait analyses showed that the associations were primarily explained by individual specific, non-shared environmental influences (>/=80%), whereas heritability explained <15% of covariation. Cardiovascular fitness changes between age 15 and 18 y predicted cognitive performance at 18 y. Cox proportional-hazards models showed that cardiovascular fitness at age 18 y predicted educational achievements later in life. These data substantiate that physical exercise could be an important instrument for public health initiatives to optimize educational achievements, cognitive performance, as well as disease prevention at the society level.
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