Search for dissertations about: "scattered radiation"

Showing result 1 - 5 of 43 swedish dissertations containing the words scattered radiation.

2. 1. Development of optimized radiation therapy using external electron and photon beams

   Author : Mats Åsell; Henk Huizenga; Stockholms universitet; []
   Keywords : Target design; Collimator Scattered Radiation; Collimator Scatter Kernel; Treatment Planning; Radiation Therapy Optimization; Intensity Modulation; Energy Modulation; Beam Modality Combinations; medicinsk strålningsfysik; Medical Radiation Physics;

   Abstract : The development of new intensity modulated radiation therapy (IMRT) techniques and treatment optimization tools makes it desirable to further improve modulation methods by using scanned photon and electron beams. It is shown that the narrowest possible photon beams have the potential to improve the flexibility in dose delivery, speed up the dose delivery and improve the treatment outcome. READ MORE

4. 2. Digital Mammography with a Photon Counting Detector in a Scanned Multislit Geometry

   Author : Magnus Åslund; Mats Danielsson; Ehsan Samei; KTH; []
   Keywords : NATURVETENSKAP; NATURAL SCIENCES; mammography; digital; photon counting; scanning; detective quantum effciency; scattered radiation; automatic exposure control; Physics; Fysik;

   Abstract : Mammography screening aims to reduce the number of breast cancer deaths by early detection of the disease, which is one of the leading causes of deaths for middle aged women in the western world. The risk from the x-ray radiation in mammography is relatively low but still a factor in the benefit-risk ratio of screening. READ MORE

5. 3. Absorbed Dose Determination and Characteristics of Degraded Electron Beams: Application to Intraoperative Radiation Therapy

   Author : Peter Björk; Internmedicin - epidemiologi; []
   Keywords : MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; Clinical physics; radiology; tomography; medical instrumentation; Klinisk fysiologi; radiologi; tomografi; medicinsk instrumentering; absorbed dose distribution; output factor; stopping-power ratio; beam characteristics; Monte Carlo calculation; electron beam dosimetry; applicator system; radiation therapy; linear accelerator; intraoperative radiotherapy;

   Abstract : The aim of this work was to quantify limitations of and uncertainties in commonly used dosimetric techniques for relative absorbed dose determination in degraded electron beams, such as those encountered in intraoperative radiation therapy (IORT) and small-electron-field radiotherapy. Three different detector types were investigated with regard to measurements of output factors and relative absorbed dose distributions: (1) a parallel-plate ionization chamber, (2) a p-type silicon diode detector and (3) a diamond detector. READ MORE

6. 4. On ionising radiation and breast cancer risk

   Author : Anders Mattsson; Karolinska Institutet; Karolinska Institutet; []
   Keywords : ionising radiation; breast cancer induction; cancer induction; risk models; risk modification; pooled analysis; mammmographic screening; gained lost years of life;

   Abstract : Background: It is well known that exposure to ionising radiation increases the risk for breast cancer occurrence. However, better understanding of breast cancer risks in terms of dose-response relationships formulated according to radiobiological target theories, age-at-exposure patterns and temporal dependence are important for the understanding of the underlying biological mechanism of radiation carcinogenesis as well as for the concern about possible risks associated with the very low doses received from routine mammographic screening. READ MORE

7. 5. Online power transformer diagnostics using multiple modes of microwave radiation

   Author : Mariana Dalarsson; Martin Norgren; Sven Nordebo; KTH; []
   Keywords : TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; inverse problem; multiple modes; power transformers;

   Abstract : In the present thesis, we propose and investigate a new approach to diagnose the effects of the various degradation mechanisms, including thermal degradation at hot spots, winding deformations due to the mechanical forces from short circuit currents, partial discharges due to local electric field surges, and increased moisture levels in the cellulose insulation due to decomposition, that affect electric power transformers during their normal operation in an electric power grid.Although the proposed diagnostics method can in principle be used to detect various degradation mechanisms mentioned above, we focus in the present thesis on mechanical deformations of transformer winding structures. READ MORE