<p>Silicon diodes compared to other types of dosimeters have several attractive properties, such as an excellent spatial resolution, a high sensitivity, and clinically practical to use. These properties make silicon diodes a preferred dosimeter for relative dosimetry for several types of measurements in small field dosimetry, e.g., stereotactic treatments and intensity modulated radiotherapy (IMRT). Silicon diodes are, however, limited by an energy dependent response variation in photon beams, resulting in that the diode readout per dose to the phantom medium varies with photon spectral changes, thereby introducing a significant uncertainty in the measured data. The traditional solution for the energy dependent over-response caused by low-energy photons is to use diodes with a shielding filter of high atomic number. These shielded diodes, however, show an incorrect readout for small fields due to electrons scattered from the shielding (Griessbach <em>et al</em>. 2005). In regions with degraded lateral electron equilibrium (LEE) shielded diodes over-respond due to an increased degree of LEE, as a consequence of the high density shielding (Lee <em>et al</em>. 2002).</p><p>In this work a prototype software that corrects for the energy dependent response of a silicon diode is developed and validated for small field sizes. The developed software is based on the novel concept of Monte Carlo (MC) simulated fluence pencil beam kernels to calculate spectra (Eklund and Ahnesjö 2008), and the spectra based silicon diode response model proposed by Eklund and Ahnesjö (2009). The software was also extended to include correction of ionization chambers, for the energy dependent Spencer-Attix water/air stopping power ratio (<em>s</em>_w,air). The calculated <em>s</em>_w,air are shown to be in excellent agreement with published values to better than 0.1% for most values, the maximum deviation being 0.3%.</p><p>Measured relative depth doses, relative profiles, and output factors in water, for small square field sizes, for 6 MV and 15 MV clinical photon beams are presented in this work. The results show that the unshielded Scanditronix-Wellhöfer EFD^3G silicon diode response, corrected by the developed software, is in excellent agreement with reference ionization chamber measurements (corrected for change in <em>s</em>_w,air), the maximum deviation being 0.4%.</p><p>Measurements with two types of shielded diodes, namely Scanditronix-Wellhöfer PFD silicon diodes (FP1990 and FP2730), are also included in this work. The shielded diodes are shown to have an over-response as large as 2-3.5% for field sizes smaller than 5 cm x 5 cm. The presented results also suggest a difference in accuracy as large as 0.5-1% between the two types of shielded diodes, where the spectral composition at the measurement position dictates which type of diode is more accurate.</p><p>The fast correction of silicon diodes provided by the developed software is more accurate than shielded diodes for small field sizes, and can in radiotherapeutic clinical practice increase the dosimetric accuracy of silicon diodes.</p>

Silicon diodes compared to other types of dosimeters have several attractive properties, such as an excellent spatial resolution, a high sensitivity, and clinically practical to use. These properties make silicon diodes a preferred dosimeter for relative dosimetry for several types of measurements in small field dosimetry, e.g., stereotactic treatments and intensity modulated radiotherapy (IMRT). Silicon diodes are, however, limited by an energy dependent response variation in photon beams, resulting in that the diode readout per dose to the phantom medium varies with photon spectral changes, thereby introducing a significant uncertainty in the measured data. The traditional solution for the energy dependent over-response caused by low-energy photons is to use diodes with a shielding filter of high atomic number. These shielded diodes, however, show an incorrect readout for small fields due to electrons scattered from the shielding (Griessbach et al. 2005). In regions with degraded lateral electron equilibrium (LEE) shielded diodes over-respond due to an increased degree of LEE, as a consequence of the high density shielding (Lee et al. 2002). In this work a prototype software that corrects for the energy dependent response of a silicon diode is developed and validated for small field sizes. The developed software is based on the novel concept of Monte Carlo (MC) simulated fluence pencil beam kernels to calculate spectra (Eklund and Ahnesjö 2008), and the spectra based silicon diode response model proposed by Eklund and Ahnesjö (2009). The software was also extended to include correction of ionization chambers, for the energy dependent Spencer-Attix water/air stopping power ratio (sw,air). The calculated sw,air are shown to be in excellent agreement with published values to better than 0.1% for most values, the maximum deviation being 0.3%. Measured relative depth doses, relative profiles, and output factors in water, for small square field sizes, for 6 MV and 15 MV clinical photon beams are presented in this work. The results show that the unshielded Scanditronix-Wellhöfer EFD3G silicon diode response, corrected by the developed software, is in excellent agreement with reference ionization chamber measurements (corrected for change in sw,air), the maximum deviation being 0.4%. Measurements with two types of shielded diodes, namely Scanditronix-Wellhöfer PFD silicon diodes (FP1990 and FP2730), are also included in this work. The shielded diodes are shown to have an over-response as large as 2-3.5% for field sizes smaller than 5 cm x 5 cm. The presented results also suggest a difference in accuracy as large as 0.5-1% between the two types of shielded diodes, where the spectral composition at the measurement position dictates which type of diode is more accurate. The fast correction of silicon diodes provided by the developed software is more accurate than shielded diodes for small field sizes, and can in radiotherapeutic clinical practice increase the dosimetric accuracy of silicon diodes.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2002. / Härtill 5 uppsatser.

Syfte och frågeställningar: Syftet är att studera om träning på olika intensitetsnivåer påverkar upplevd stress hos kvinnor i Sverige. Denna studie kommer svara på dessa frågeställningar:  <ol type="1">Finns det någon skillnad i upplevd stress hos kvinnor som deltar på lågintensiv träning i form av promenader jämfört med kvinnor som deltar på högintensiv träning i form av löpning? Finns det någon skillnad i upplevd stress hos kvinnor som deltar på högintensiv träning i form av löpning jämfört med kvinnor som inte tränar alls? Finns det någon skillnad i upplevd stress hos kvinnor som deltar på lågintensiv träning i form av promenader jämfört med kvinnor som inte tränar alls?           Metod: Studien är en tvärsnittsstudie, genom enkätundersökningar har skillnader i upplevd stress jämförts på kvinnor med medelålder 39,03 år ( ± 14,44), som antingen tränat högintensivt eller lågintensivt. Resultaten har jämförts med en referensgrupp bestående av kvinnor som inte tränar alls. Perceived Stress Scale-10 (PSS10) inklusive tio stycken intensitets-frågor för inklusion i studien skickades ut via sociala medier, Facebook. Resultat: En signifikant skillnad sågs vid jämförandet av kvinnor som tränar högintensivt och referensgrupp, (p=0,001), poängmässig skillnad i PSS10; 7,67 poäng. Ingen signifikant skillnad redovisades mellan högintensiv och lågintensiv grupp (p=0,737), detsamma gällde lågintensiv och referensgrupp (p=0,081). Slutsats: Högintensiva kvinnor hade reducerad upplevd stress jämfört med kvinnor som inte tränade alls. Ingen skillnad i upplevd stress kunde urskiljas mellan kvinnor som tränar lågintensivt och kvinnor som tränade högintensivt. Samma gällde kvinnor som tränade på låg intensitet jämfört med kvinnor som inte tränade alls, ingen skillnad i upplevd stress. / Purpose and aims: The aim is to study if different exercise-intensities affects perceived stress in Swedish women. This study will answer the following questions: <ol type="1">Is there a difference in perceived stress in women who participate in low-intensity exercise in the form of walking compared to women who participate in high-intensity exercise in the form of running? Is there a difference in perceived stress in women who participate in high-intensity exercise in the form of running compared to women who do not exercise at all? Is there a difference in perceived stress in women who participate in low-intensity exercise in the form walking compared to women who do not exercise at all?           Method: The study is a cross-sectional study, through questionnaires, differences in perceived stress have been compared in women with a mean age of 39,03 years (± 14,44), who either exercised with high intensity or with low intensity. The results have been compared to a reference group consisting of non-training women. Perceived Stress Scale-10 (PSS10) together with ten intensity-questions for inclusion in the study was sent out via social media, Facebook. Results: A significant difference was detected in the comparison of the high intensity group and the reference group, (p=0.001), score difference in PSS10; 7,67 points. No significant difference between the high-intensity group and the low-intensity group (p=0.737), the same applied to the low-intensity group and the reference group (p=0,081). Conclusions: Women who participated in high intensity exercise had reduced percieved stress compared to women who did not exercise at all. No difference in percieved stress was observed between women who participated in low intensity exercise and women who participated in high intensity exercise. Similarly, no difference in percieved stress in women who participated in low intensity exercise and women who did not exercise at all.