<p>In this project several tests were performed to evaluate the performance of an On-Board Imager® (OBI) mounted on a clinical linear accelerator. The measurements were divided into three parts; geometric accuracy, image registration and couch shift accuracy, and image quality. A cube phantom containing a radiation opaque marker was used to study the agreement with treatment isocenter for both kV-images and cone-beam CT (CBCT) images. The long term stability was investigated by acquiring frontal and lateral kV images twice a week over a 3 month period. Stability in vertical and longitudinal robotic arm motion as well as the stability of the center-of-rotation was evaluated. Further, the agreement of kV image and CBCT center with MV image center was examined.</p><p>A marker seed phantom was used to evaluate and compare the three applications in image registration; 2D/2D, 2D/3D and 3D/3D. Image registration using kV-kV image sets were compared with MV MV and MV-kV image sets. Further, the accuracy in 2D/2D matches with images acquired at non-orthogonal gantry angles was evaluated. The image quality in CBCT images was evaluated using a Catphan® phantom. Hounsfield unit (HU) uniformity and linearity was compared with planning CT. HU accuracy is crucial for dose verification using CBCT data.</p><p>The geometric measurements showed good long term stability and accurate position reproducibility after robotic arm motions. A systematic error of about 1 mm in lateral direction of the kV-image center was detected. A small difference between kV and CBCT center was observed and related to a lateral kV detector offset. The vector disagreement between kV- and MV-image centers was  2 mm at some gantry angles. Image registration with the different match applications worked sufficiently. 2D/3D match was seen to correct more accurately than 2D/2D match for large translational and rotational shifts. CBCT images acquired with full-fan mode showed good HU uniformity but half fan images were less uniform. In the soft tissue region the HU agreement with planning CT was reasonable while a larger disagreement was observed at higher densities. This work shows that the OBI is robust and stable in its performance. With regular QC and calibrations the geometric precision of the OBI can be maintained within 1 mm of treatment isocenter.</p>

<p>Magnetic Resonance Imaging, MRI, is a diagnostic tool in progress which has been available at major hospitals since the mid eighties. Today almost all hospitals world wide may depict the human body with their own MRI scanner. MRI is dependent on a uniform magnetic field inside the scanner tunnel and Radio frequent (RF) waves used for excitation of the magnetic dipole moments in the body. These properties along with the magnetic field surrounding the scanner are associated with dangerous effects - when interacting with medical implants made of metals. These dangerous effects are twisting forces or torques, heating and translational forces respectively. A database containing information about known implants behaviour regarding these effects among with earlier documentation and information concerning MRI patient safety at Karolinska hospital, Huddinge was constructed.</p><p>Also a phantom used for heating effect measurements was constructed and heating effect measurements were performed at a SPC4129 locking titanium Peritoneal Dialysis (PD) catheter adapter and a Deep Brain Stimulator (DBS) in order to test the phantom and confirm the theory about RF induced heating on medical implants. Evidence for heating effects caused by the implants was found.</p><p>A torque measurement apparatus was constructed and measurements were performed. All measurements where performed in order to investigate the functionality of the apparatus and also the theory behind dangerous magnetically induced torques (twisting movements). Substantial torque were measured on the ferromagnetic device used for the test.</p><p>The heating phantom and torque measurement apparatus is slightly modified models of those proposed by ASTM (American Society for Testing and Materials).</p>

<p>Since 1986 patients with ocular malignant melanoma have been treated with Ru-106 plaques at S:t Erik Eye Hospital. In 1998 I-125 radioactive seed plaques was presented as an alternative to Ru-106 when treating tumors with an apical height greater than 7 mm. Until June 2005 the doseplanning of these plaques was based on a depth-dose curve made in the dose planning system Cadplan supplied by Varian Medical Systems. In the recent years the capabilities of computerized 3D dose planning system has increased greatly. The number of types of seeds on the market has also increased.</p><p>In order to implement the modern 3D dose planning system Brachy Vision 7.3.10 in planning the I-125 plaques, a review of the dose planning process have been done.</p><p>The ultra sound equipment used by the ophthalmologist to determine the apical height of the tumor has been investigated in terms of accuracy. A phantom has been developed for this task.</p><p>As new seeds entered the market a comparision have been made comparing the Amersham 6711 seed with the Bebig I25.S06 seed. A method for measuring the activity of the single seeds has also been developed.</p><p>The dose planning system Brachy Vision 7.3.10 have been compared to the old dose planning method, and an implementation of the plaques into Brachy Vision have been made.</p><p>The ultra sound equipment was accurate in the regions of interest. It was also discovered that the Bebig I25.S06 seed gave slightly higher dose compared to the Amersham 6711 with the same activity. The difference between the seeds is however small. The results indicate that the old dose planning method gave a slight underdosage.</p>

<p>The aim of this work is to characterize the beam of the 60Co therapy unit “Siemens Gammatron 1”, used at the Swedish Radiation Protection Authority (SSI) to calibrate therapy level ionization chambers. SSI wants to know the spectra in the laboratory’s reference points and a verified, virtual model of the 60Co unit to be able to compare current and future experiments to Monte Carlo simulations.</p><p>EGSnrc is a code for performing Monte Carlo simulations. By using BEAMnrc, which is an additional package that simplifies the building process of a geometry in the EGS-code, the whole Gammatron at SSI was defined virtually. In this work virtual models for two experimental setups were built: the Gammatron irradiating in air to simulate the air-kerma calibration geometry and the Gammatron irradiating a water phantom similar to that used for the absorbed dose to water calibrations.</p><p>The simulations are divided into two different substeps: one for the fixed part of the Gammatron and one for the variable part to be able to study different entities and to shorten simulation times.</p><p>The virtual geometries are verified by comparing Monte Carlo results with measurements. When it was verified that the virtual geometries were to be trusted, they were used to generate the Gammatron photon spectra in air and water with different field sizes and at different depths. The contributions to the photon spectra from different regions in the Gammatron were also collected. This is something that is easy to achieve with Monte Carlo calculations, but difficult to obtain with ordinary detectors in real life measurements.</p><p>The results from this work give SSI knowledge of the photon spectra in their reference points for calibrations in air and in water phantom. The first step of the virtual model (fixed part of Gammatron) can be used for future experimental setups at SSI.</p>

<p>Interventional radiological procedures often require long fluoroscopic exposure times and high levels of radiation exposure to patients, which often are higher than most radiological examinations except for computed tomography (CT) whose effective doses can be higher, and in addition to having radiation risks that are higher for both patient and medical staff. Therefore it is important to monitor and map the radiation entrance exposure to the patients, to minimize the probability of skin injury, and to detect areas of overlapping radiation fields. The aim of this thesis is to evaluate patient doses in interventional radiology procedures using a new GAFCHROMIC-XR TYPE R DOSIMETER MEDIA X-ray Dosimetry film, which allows mapping of the skin dose distribution, when placed closer to the skin. These radiochromic films can be characterized by a power response dose function when plotting pixel value versus air kerma and have been calibrated up to 5 Gy when using a flatbed scanner. Image analysis was performed using the red channel component of standard the RGB (Red, Green, and Blue) color space image. The association between the Maximum Entrance Skin Doses (MESD) and Dose Area Product (DAP) values for two interventional procedures; coronary angiography (CA), and percutaneous transluminal coronary angiography (PTCA) is investigated.</p>

<p>A commercially available amorphous silicon electronic portal imaging device (EPID) was studied with regard to its dosimetric properties and to determine its usefulness as a tool for dosimetric pre-treatment verification of radiotherapy treatment fields. The dosimetric properties that were studied include reproducibility over time, linearity with dose, dose rate dependence and ghosting effects. The pre-treatment verification is performed by acquiring dosimetric images with the EPID and comparing these images with predicted images, calculated by the treatment planning system. This method for verification was evaluated. Also, the calibration and configuration of the treatment planning system and of the EPID for dosimetric verification was performed and is presented here.</p><p>The dosimetric properties of the EPID were found to be suitable for the measurements for which it is intended. It is linear with dose and does not show significant dose rate dependence or ghosting effects. As a pre-treatment verification system it is accurate within 3% and 3mm for ~99% of a region around the irradiated area of the image.</p>

<p>The use of MRI for patient examinations has constantly increased as technical development has lead to faster image acquisitions and higher image quality. Nevertheless, an MR-examination still takes relatively long time and yet another way of speeding up the process is to employ parallel imaging. In this thesis, one of these parallel imaging techniques, called SENSE, is described and examined more closely.</p><p>When SENSE is employed, the number of spatial encoding steps can be reduced thanks to the use of several receiving coils. A reduction of the number of phase encoding steps not only leads to faster image acquisition, but also to superimposed pixel values in image space. In order to be able to separate the aliased pixels, knowledge about the spatial sensitivity of the coils is required.</p><p>There are several different alternatives to how and when information about the sensitivities of the coils should be collected, but in this thesis, focus is on the method of performing a reference measurement before the actual scan. The reference measurement consists of a fast, low-resolution sequence which either is collected with both the body coil and the parallel imaging coil or only with the parallel imaging coil. A comparison of these two methods by simulations in program written MATLAB leads to the conclusion that even if the scan time of the reference measurement is doubled it seems like there are numerous advantages of also collecting data with the body coil:</p><p>• the images are more homogeneous which facilitates the establishment of a diagnose</p><p>• the noise levels in the reconstructed images are somewhat lower</p><p>• images collected with a reduced sampling density show better agreement with those collected without reduction.</p><p>Furthermore, it is shown that the reference measurement preferably should be a 3D sequence covering all the volume of interest. If a 2D sequence is used it is absolutely necessary that it can be performed in any plane and it has to be repeated for every plane that is imaged.</p>

<p>A method to establish the boundaries of the sensitive volume for a chosen detector to within 50µm (as specified by Elekta Instuments AB) was investigated and is presented in this project. The detector studied was fixed to a positioning system with possibility to move with sub micrometer increments, and scanned in a narrow photon field. The detectors used for the experiment were silicon diodes and a pair of diamond detectors. The silicon diodes showed great promise for future study; two radiotherapy silicon diodes and one electrical component silicon diode were used. The electrical component silicon diode produced a surprisingly sharp dose profile compared with the medical silicon diodes. The diamond detectors gave no stable results at all.</p><p>As a radiation source 60Co proved most feasible, but a diagnostic x-ray source was also tested as well as a 99mTc source. These radiation sources were also examined with a modified Penelope code, i.e. Monte Carlo simulations. What became very obvious with the Monte Carlo simulations was the importance of the line up, which was never satisfactory.</p><p>To limit the sensitive volume of these detectors to within the desired boundaries showed great difficulty and was not achieved in this project.</p>

<p>Purpose: The aim of this thesis is to study the European (ESTRO/EAU/EORTC) and American (ABS) guidelines how to report the permanent seed implant and the most significant dosimetric parameters. It will also report on the permanent seed implant at Södersjukhuset, Karolinska University Hospital according to the guidelines. A large number of studies on pre- and post-implant dosimetry on permanent seed implants have recently been published but none is considered a standard. This makes it difficult, if not impossible, to compare data from different centres. The differences in reporting will also be discussed in this thesis. Another part of the study is to investigate how the morbidity correlates with the dose. The results in this report will give an overview of the experience at Södersjukhuset.</p><p>Matherials and Methods: This study includes 198 patients who received implants between 2004-2007 with I-125 seeds under transperineal ultrasound at Södersjukhuset (to a prescribed dose of 145 Gy). The dose-planning system VariSeed 7.1 was used with an online connection to the ultrasound system with real-time verification. Dose constraints for the planning system are V(100)>99%, V(150)>60%, V(200)>25%, UrD(10)<130% and UrD(30)<125%. Outer and inner wall of rectum was outlined for 55 patients as recommended by ESTRO/EAU/EORTC and doses to rectum were also computed.</p><p>Results: The median value for dosimetric parameters at Södersjukhuset, Karolinska University Hospital are for the prostate; D(90)=174Gy (153-194Gy), V(100)= 99% (93-100%), V(150)= 57% (40-74%), for the urethra; UrD(30) = 130% (112-147%), UrD(10) = 124% (107-142%) and for the rectum; RD2cc= 98Gy (73-128Gy), RD0.1cc=164Gy (119-240Gy), RV(100)=0.3cc (0.0-1.3cc), RV(150)=0.0cc (0.0-0.2cc). These values correspond to recommended data, except for the V(150) value. Regarding the clinically observed results, 3 patients had a relapse in their cancer, 2 patients had mild proctitis and 15 patients had urinary problems.</p><p>Discussion and Conclusions: The significant dosimetric parameters for reporting according to ESTRO/EAU/EORTC and ABS for prostate are D90[Gy], V(100)[%] and V(150)[%], for urethra are D(30) and D(10), and for rectum RD2cc and RD0.1cc. These parameters consider as a minimum to use and they further recommend secondary parameters to report. Other authors have also recommended to report RV(100) and RV(150) for rectum. This study did not show any relationship between UrD(10), UrD(30) and urinary morbidity. According to the recommendations every patient should undergo a CT-based evaluation. Further investigations are needed on whether a post-implant CT-study is necessary for real-time implantation, as there is not enough published data on this aspect.</p>

<p>One of the most used irradiation techniques in modern radiation therapy is step-and-shoot IMRT. The accuracy of this technique when delivering complex dose distributions strongly depends on the size of the subfields. The aims of this study is to determine the minimum size of subfields that can be used efficiently in Step-and-Shoot IMRT, to investigate the validation process for beam delivery and treatment planning dose calculations, and to find recommendations for practical clinical implementations.</p><p>Two different detectors, a CC04 ion chamber and a SFD stereotactic diode, have been used for measuring head scatter factors in air (Sc), total output factors (Scp) and dose profiles in water for a wide range of field sizes. The measurements were compared to calculations done with a pre-release version of the Nucletron MasterPlanTM v 3.1 treatment planning system that employs a novel, high resolution fluence modelling for both its pencil beam and collapsed cone dose calculation algorithms. Collimator settings were explicitly checked using FWHM film measurements with a build-up sheet of tungsten placed close to the treatment head to reduce the influence from lateral electron transport and geometrical penumbra. An analysis of the influence and sensitivity of Scp for small fields with respect to the linear accelerator source size and shape was also made.</p><p>The measurements with the ionization chamber and the stereotactic diode showed good agreements with each other and with the treatment planning system calculations for field sizes larger than 2×2 cm2. For small field sizes, measurements with different detectors yielded different results. Calculations showed agreements with measurements with the smallest detector, provided careful field size calibration and commissioning of calculation parameters. Uncertainties in collimator settings and source characteristics were shown to yield large uncertainties in Scp for fields smaller than 2×2 cm2.</p><p>The treatment planning system was found to properly handle small subfields but results were very sensitive to uncertainties in source size, as well as calibration and reproducibility of the collimator settings. Therefore if subfields smaller than 2×2 cm2 are to be used in IMRT extra care should be taken to determine the source characteristics and to calibrate the collimators. The volume of the detectors used for validation of such small fields and the loss of charged particle equilibrium conditions also have to be taken into consideration.</p>