| 1. |
- Alevronta, Eleftheria, et al.
(författare)
-
Dose-response relationships for an atomized symptom of fecal incontinence after gynecological radiotherapy.
- 2013
-
Ingår i: Acta oncologica (Stockholm, Sweden). - : Taylor & Francis. - 1651-226X .- 0284-186X. ; 52:4, s. 719-26
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose. The aim of this study was to investigate what bowel organ and delivered dose levels are most relevant for the development of 'emptying of all stools into clothing without forewarning' so that the related dose-responses could be derived as an aid in avoiding this distressing symptom in the future. Material and methods. Of the 77 gynecological cancer survivors treated with radiotherapy (RT) for gynecological cancer, 13 developed the symptom. The survivors were treated between 1991 and 2003. The anal-sphincter region, the rectum, the sigmoid and the small intestines were all delineated and the dose-volume histograms were exported for each patient. The dose-volume parameters were estimated fitting the data to the Relative Seriality (RS), the Lyman and the generalized Equivalent Uniform Dose (gEUD) model. Results. The dose-response parameters for all three models and four organs at risk (OARs) were estimated. The data from the sigmoid fits the studied models best: D50 was 58.8 and 59.5 Gy (RS, Lyman), γ50 was 1.60 and 1.57 (RS, Lyman), s was 0.32, n was 0.13 and a was 7.7 (RS, Lyman, gEUD). The estimated volume parameters indicate that the investigated OARs behave serially for this endpoint. Our results for the three models studied indicate that they have the same predictive power (similar LL values) for the symptom as a function of the dose for all investigated OARs. Conclusions. In our study, the anal-sphincter region and sigmoid fit our data best, but all OARs were found to have steep dose-responses for 'emptying of all stools into clothing without forewarning' and thus, the outcome can be predicted with an NTCP model. In addition, the dose to the four studied OARs may be considered when minimizing the risk of the symptom.
|
|
| 2. |
- Ashwear, Nasseradeen, 1968-
(författare)
-
Vibration Frequencies as Status Indicators for Tensegrity Structures
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Applications of vibration structural health monitoring (VHM) techniques are increasing rapidly. This is because of the advances in sensors and instrumentation during the last decades. VHM uses the vibration properties to evaluate many civil structures during the design steps, building steps and service life.The stiffness and frequencies of tensegrity structures are primarily related to the level of pre-stress. The present work investigates the possibilities to use this relation in designing, constructing and evaluating the tensegrity structures.The first part of the present work studies the improvement of current models for resonance frequency simulation of tensegrities by introducing the bending behaviour of all components, and by a one-way coupling between the axial force and the stiffness. From this, both local and global vibration modes are obtained. The resonance frequencies are seen as non-linearly dependent on the pre-stress level in the structure, thereby giving a basis for diagnosis of structural conditions from measured frequencies. The new aspects of tensegrity simulations are shown for simple, plane structures but the basic methods are easily used also for more complex structures.In the second part, the environmental temperature effects on vibration properties of tensegrity structures have been investigated, considering primarily seasonal temperature differences (uniform temperature differences). Changes in dynamic characteristics due to temperature variations were compared with the changes due to decreasing pre-tension in one of the cables. In general, it is shown that the change in structural frequencies made by temperature changes could be equivalent to the change made by damage (slacking). Different combinations of materials used and boundary conditions are also investigated. These are shown to have a significant impact on the pre-stress level and the natural frequencies of the tensegrity structures when the environment temperature is changed.
|
|
| 3. |
- Dahlblom, Ola, 1956, et al.
(författare)
-
Strukturmekanik - modellering och analys
- 2010
-
Bok (övrigt vetenskapligt/konstnärligt)abstract
- Strukturmekanik är den del av fysiken som beskriver hur olika material, som formats och sammanfogats till strukturer, bär sina laster. Kunskapen om dessa strukturers verkningssätt kan användas i en skapande process där hållbara och effektiva, funktionella och uttrycksfulla byggnadsverk utformas. Den här läroboken i strukturmekanik baseras på finita elementmetodens metodik. Förståelsen för strukturmekaniska grundelement, fjädrar, stänger, balkar och fundament, byggs successivt upp i en, två och tre dimensioner. Med hjälp av dessa element visas hur komplexa bärande konstruktioner kan modelleras och analyseras. Metoder för såväl linjär som geometriskt och materiellt ickelinjär analys presenteras. För att synliggöra den beskrivna metodikens generalitet finns ett kort avsnitt som tar upp andra områden inom tillämpad mekanik som värmeledning och elektrisk strömning. Läroboken stödjer tre centrala lärandemål: • Kunskap i grundläggande strukturmekanisk teori. • Färdighet i att modellera och analysera strukturer. • Förmåga att i en designprocess värdera och effektivisera föreslagna konstruktionsutformningar.Läroboken vänder sig till civilingenjörsstudenter på kandidatnivå och till högskoleingenjörsstudenter. Datorprogram som stöder bokens framställning finns att fritt ladda ner från hemsidan www.studentlitteratur.se/strukturmekanik.
|
|
| 4. |
- Dahlblom, Ola, et al.
(författare)
-
Strukturmekanik - Modellering och analys av ramar och fackverk
- 2010
-
Bok (övrigt vetenskapligt/konstnärligt)abstract
- Strukturmekanik är den del av fysiken som beskriver hur olika material, som formats och sammanfogats till strukturer, bär sina laster. Kunskapen om dessa strukturers verkningssätt kan användas i en skapande process där hållbara och effektiva, funktionella och uttrycksfulla byggnadsverk utformas. Den här läroboken i strukturmekanik baseras på finita elementmetodens metodik. Förståelsen för strukturmekaniska grundelement, fjädrar, stänger, balkar och fundament, byggs successivt upp i en, två och tre dimensioner. Med hjälp av dessa element visas hur komplexa bärande konstruktioner kan modelleras och analyseras. Metoder för såväl linjär som geometriskt och materiellt ickelinjär analys presenteras. För att synliggöra den beskrivna metodikens generalitet finns ett kort avsnitt som tar upp andra områden inom tillämpad mekanik som värmeledning och elektrisk strömning. Läroboken stödjer tre centrala lärandemål: • Kunskap i grundläggande strukturmekanisk teori. • Färdighet i att modellera och analysera strukturer. • Förmåga att i en designprocess värdera och effektivisera föreslagna konstruktionsutformningar. Läroboken vänder sig till civilingenjörsstudenter på kandidatnivå och till högskoleingenjörsstudenter. Datorprogram som stöder bokens framställning finns att fritt ladda ner från hemsidan www.studentlitteratur.se/strukturmekanik.
|
|
| 5. |
- Dalilsafaei, Seif
(författare)
-
Stiffness modification of tensegrity structures
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the concept of tensegrity structures was invented in the beginning of the twentieth century, the applications of these structures are limited, partially due to their low stiffness. The stiffness of tensegrities comes from topology, configuration, pre-stress and initial axial element stiffnesses. The first part of the present work is concerned with finding the magnitude of pre-stress. Its role in stiffness of tensegrity structures is to postpone the slackening of cables. A high pre-stress could result in instability of the structure due to buckling and yielding of compressive and tension elements, respectively. Tensegrity structures are subjected to various external loads such as self-weight, wind or snow loads which in turn could act in different directions and be of different magnitudes. Flexibility analysis is used to find the critical load combinations. The magnitude of pre-stress, in order to sustain large external loads, is obtained through flexibility figures, and flexibility ellipsoids are employed to ensure enough stiffness of the structure when disturbances are applied to a loaded structure. It has been seen that the most flexible direction is very much sensitive to the pre-stress magnitude and neither analytical methods nor flexibility ellipsoids are able to find the most flexible directions. The flexibility figures from a non-linear analysis are here utilized to find the weak directions. In the second part of the present work, a strategy is developed to compare tensegrity booms of triangular prism and Snelson types with a truss boom. It is found that tensegrity structures are less stiff than a truss boom when a transversal load is applied. An optimization approach is employed to find the placement of the actuators and their minimum length variations. The results show that the bending stiffness can be significantly improved, but still an active tensegrity boom is less stiff than a truss boom. Genetic algorithm shows high accuracy of searching non-structural space.
|
|
| 6. |
|
|
| 7. |
- Pettersson, Niclas, 1974, et al.
(författare)
-
A method to estimate composite doses for organs at risk in prostate cancer patients treated with EBRT in combination with HDR BT.
- 2014
-
Ingår i: Acta oncologica (Stockholm, Sweden). - 1651-226X. ; 53:6, s. 815-821
-
Tidskriftsartikel (refereegranskat)abstract
- Background. When evaluating late toxicity after combined external beam radiation therapy (EBRT) and high-dose rate brachytherapy (HDR BT) prostate cancer treatments, it is important that the composite dose distribution is taken into account. This can be challenging if organ-at-risk (OAR) dose data are incomplete, i.e. due to a limited ultrasound imaging field-of-view in the HDR BT procedure. This work proposes a method that provides estimates of composite OAR doses for such situations. Material and methods. Original EBRT, simulated HDR BT, and composite dose-volume histograms (DVHs) for 10 pelvic OARs in 30 prostate cancer cases were used for method implementation and evaluation (EBRT: 25 × 2.0 Gy + BT: 2 × 10.0 Gy). The proposed method used information from the EBRT DVH to estimate OAR BT doses (with or without fractionation correction). Coefficients of determination (R(2)) were calculated for linear relationships between several EBRT DVH parameters and a BT DVH parameter of interest. The largest R(2) value decided the relationship that best predicted the BT DVH parameter. The composite dose value was then calculated by adding the EBRT DVH and the estimated BT DVH parameter values and was compared to the reference composite value (in 1200 OAR/patient/parameter cases). Results. The linear relationships had an average R(2) of 0.68 (range 0.42-0.88). Only one ninth of the 1200 estimated composite DVH values differed more than 2 Gy from their reference values. Conclusion. Given a successful implementation, the proposed method only requires original or simulated BT plan data for a subset of patients to estimate composite doses for large study populations in a time-efficient manner. This can assist in evaluating radiation-induced late toxicity in multimodality treatments with limited OAR dose data.
|
|
| 8. |
|
|
| 9. |
- Waldenström, Ann-Charlotte, 1950, et al.
(författare)
-
Pain and mean absorbed dose to the pubic bone after radiotherapy among gynecological cancer survivors.
- 2011
-
Ingår i: International journal of radiation oncology, biology, physics. - : Elsevier. - 1879-355X .- 0360-3016. ; 80:4, s. 1171-1180
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To analyze the relationship between mean absorbed dose to the pubic bone after pelvic radiotherapy for gynecological cancer and occurrence of pubic bone pain among long-term survivors.METHODS AND MATERIALS: In an unselected, population-based study, we identified 823 long-term gynecological cancer survivors treated with pelvic radiotherapy during 1991-2003. For comparison, we used a non-radiation-treated control population of 478 matched women from the Swedish Population Register. Pain, intensity of pain, and functional impairment due to pain in the pubic bone were assessed with a study-specific postal questionnaire.RESULTS: We analyzed data from 650 survivors (participation rate 79%) with median follow-up of 6.3 years (range, 2.3-15.0 years) along with 344 control women (participation rate, 72 %). Ten percent of the survivors were treated with radiotherapy; ninety percent with surgery plus radiotherapy. Brachytherapy was added in 81%. Complete treatment records were recovered for 538/650 survivors, with dose distribution data including dose-volume histograms over the pubic bone. Pubic bone pain was reported by 73 survivors (11%); 59/517 (11%) had been exposed to mean absorbed external beam doses <52.5 Gy to the pubic bone and 5/12 (42%) to mean absorbed external beam doses ≥ 52.5 Gy. Thirty-three survivors reported pain affecting sleep, a 13-fold increased prevalence compared with control women. Forty-nine survivors reported functional impairment measured as pain walking indoors, a 10-fold increased prevalence.CONCLUSIONS: Mean absorbed external beam dose above 52.5 Gy to the pubic bone increases the occurrence of pain in the pubic bone and may affect daily life of long-term survivors treated with radiotherapy for gynecological cancer.
|
|
| 10. |
- Waldenström, Ann-Charlotte, 1950, et al.
(författare)
-
Relative importance of hip and sacral pain among long-term gynecological cancer survivors treated with pelvic radiotherapy and their relationships to mean absorbed doses.
- 2012
-
Ingår i: International Journal of Radiation Oncology, Biology, Physics. - : Elsevier. - 0360-3016 .- 1879-355X. ; 84:2, s. 428-436
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To investigate the relative importance of patient-reported hip and sacral pain after pelvic radiotherapy (RT) for gynecological cancer and its relationship to the absorbed doses in these organs.METHODS AND MATERIALS: We used data from a population-based study that included 650 long-term gynecological cancer survivors treated with pelvic RT in the Gothenburg and Stockholm areas in Sweden with a median follow-up of 6 years (range, 2-15) and 344 population controls. Symptoms were assessed through a study-specific postal questionnaire. We also analyzed the hip and sacral dose-volume histogram data for 358 of the survivors.RESULTS: Of the survivors, one in three reported having or having had hip pain after completing RT. Daily pain when walking was four times as common among the survivors compared to controls. Symptoms increased in frequency with a mean absorbed dose >37.5 Gy. Also, two in five survivors reported pain in the sacrum. Sacral pain also affected their walking ability and tended to increase with a mean absorbed dose >42.5 Gy.CONCLUSIONS: Long-term survivors of gynecological cancer treated with pelvic RT experience hip and sacral pain when walking. The mean absorbed dose was significantly related to hip pain and was borderline significantly related to sacral pain. Keeping the total mean absorbed hip dose below 37.5 Gy during treatment might lower the occurrence of long-lasting pain. In relation to the controls, the survivors had a lower occurrence of pain and pain-related symptoms from the hips and sacrum compared with what has previously been reported for the pubic bone.
|
|
