Despite their unmatched soft-tissue contrast, Magnetic Resonance (MR) images suffer from wide-ranging image distortions; this has raised questions about their suitability as an imaging modality upon which to base conformal radiation therapy treatment plans. This thesis addresses image distortion as it relates to the implementation of MR-based radiation therapy treatment planning (MR-RTP). A grid phantom was imaged at 3T to determine the 3D distortion field using in-house software. Using multiple images, both machine- and object-related sources of distortion were separated such that individual evaluation of distortion sources is possible. Over the imaging volume, nonlinearities in the gradients led to peak-to-peak image distortions of up to 11 mm. For in-vivo distortion quantification, the method was augmented with a modified gradient echo sequence which measures the phase evolution due to underlying field inhomogeneities. The amount of distortion measured using this technique is dependent upon both patient anatomy and sequence parameters, but was found to contribute 5.7 mm at maximum. The methods presented can be combined to provide comprehensive distortion rectification such that mean residual image distortion is reduced to well below the pixel resolution. Finally, distortion quantification and correction methods were applied to a clinical MR-RTP study of prostate patients. The dosimetric consequences of distortion correction were investigated by comparing 3D conformal and intensity modulated radiation therapy plans developed based on both uncorrected and corrected MRI data sets. Total image distortions and those directly affecting the prostate and organs at risk (OARs) were assessed and target doses, OAR doses, and dose volume histograms were compared. Maximum distortion (from all sources) was 7.8 mm. With the exception of two patients, changes in plan dosimetry were insignificant (<2% / <1Gy). Two patients who were poorly position suffered larger distortions in the target region which led to dosimetric differences of up to 4.2%. / Medical Physics

External radiotherapy with proton and ion beams needs accurate tools for the dosimetric characterization of treatment fields. Monte Carlo (MC) particle transport codes, such as FLUKA and GEANT4, can be a valuable method to increase accuracy of dose calculations and to support various aspects of ion beam therapy (IBT), such as treatment planning and monitoring. One of the prerequisites for such applications is however that the MC codes are able to model reliably and accurately the relevant physics processes. As a first focus of this thesis work, physics models of MC codes with importance for IBT are developed and validated with experimental data. As a result suitable models and code configurations for applications in IBT are established. The accuracy of FLUKA and GEANT4 in describing nuclear fragmentation processes and the production of secondary charged nuclear fragments is investigated for carbon ion therapy. As a complementary approach to evaluate the capability of FLUKA to describe the characteristics of mixed radiation fields created by ion beams, simulated microdosimetric quantities are compared with experimental data. The correct description of microdosimetric quantities is also important when they are used to predict values of relative biological effectiveness (RBE). Furthermore, two models describing Compton scattering and the acollinearity of two-quanta positron annihilation at rest in media were developed, validated and integrated in FLUKA. The detailed description of these processes is important for an accurate simulation of positron emission tomography (PET) and prompt-γ imaging. Both techniques are candidates to be used in clinical routine to monitor dose administration during cancer treatments with IBT. The second objective of this thesis is to contribute to the development of a MC-based treatment planning tool for protons and ions with atomic number Z ≤ 8 using FLUKA. In contrast to previous clinical FLUKA-based MC implementations for IBT which only re-calculate a given treatment plan, the developed prototype features inverse optimization of absorbed dose and RBE-weighted dose for single fields and simultaneous multiple-field optimization for realistic treatment conditions. In a study using this newly-developed tool, the robustness of IBT treatment fields to uncertainties in the prediction of RBE values is investigated, while comparing different optimization strategies. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Submitted. Paper 6: Manuscript.</p>

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No description available.

The modern day radiotherapy treatments are almost exclusively based on computed tomography (CT) images. The CT images are acquired using x-rays, and therefore reflect the radiation interaction properties of the material. This information is used to perform accurate dose calculation by the treatment planning system, and the data is also well suited for creating digitally reconstructed radiographs for comparing patient set up at the treatment machine where x-ray images are routinely acquired for this purpose. The magnetic resonance (MR) scanner has many attractive features for radiotherapy purposes. The soft tissue contrast as compared to CT is far superior, and it is possible to vary the sequences in order to visualize different anatomical and physiological properties of an organ. Both of these properties may contribute to an increase in accuracy of radiotherapy treatment. Using the MR images by themselves for treatment planning is, however, problematic. MR data reflects the magnetic properties of protons, and thus have no connection to the radiointeraction properties of the material. MRI also has inherent difficulty in imaging bone, which will appear in images as areas of no signal similar to air. This makes both dose calculation and patient positioning at the treatment machine troublesome. There are several clinics that use MR images together with CT images to perform treatment planning. The images are registered to a common coordinate system, a process often described as image fusion. In these cases, the MR images are primarily used for target definition and the CT images are used for dose calculations. This method is now not ideal, however, since the image fusion may introduce systematic uncertainties into the treatment due to the fact that the tumor is often able to move relatively freely with respect to the patients’ bony anatomy and outer contour, especially when the image registration algorithms take the entire patient anatomy in the volume of interest into account. The work presented in the thesis “Integration of MRI into the radiotherapy workflow” aim towards investigating the possibilities of workflows based entirely on MRI without using image registration, as well as workflows using image registration methods that are better suited for targets that can move with respect to surrounding bony anatomy, such as the prostate. / Modern strålterapi av cancer baseras nästan helt på datortomografiska (CT) bilder. CT bilder tas med hjälp av röntgenfotoner, och återger därför hur det avbildade materialet växelverkar med strålning. Denna information används för att utföra noggranna dosberäkningar i ett dosplaneringssystem, och data från CT bilder lämpar sig också väl för att skapa digitalt rekonstruerade röntgenbilder vilka kan användas för att verifiera patientens position vid behandling. Bildgivande magnetresonanstomografi (MRI) har många egenskaper som är intressanta för radioterapi. Mjukdelskontrasten i MR bilder är överlägsen CT, och det är möjligt att i stor utstäckning variera sekvensparametrar för att synliggöra olika anatomiska och funktionella attribut hos ett organ. Dessa bägge egenskaper kan bidra till ökad noggrannhet i strålbehandling av cancer. Att använda enbart MR bilder som planeringsunderlag för radioterapi är dock problematiskt. MR data reflekterar magnetiska attribut hos protoner, och har därför ingen koppling till materialets egenskaper då det gäller strålningsväxelverkan. Dessutom är det komplicerat att avbilda ben med MR; ben uppträder som områden av signalförlust i bilderna, på samma sätt som luft gör. Detta gör det svårt att utföra noggranna dosberäkningar och positionera patienten vid behandling. Många moderna kliniker använder redan idag MR tillsammans med CT under dosplanering. Bilderna registreras till ett gemensamt koordinatsystem i en process som kallas bildfusion. I dessa fall används MR bilderna primärt som underlag för utlinjering av tumör, eller target, och CT bilderna används som grund för dosberäkningar. Denna metod är dock inte ideal, då bildregistreringen kan införa systematiska geometriska fel i behandlingen. Detta på grund av att tumörer ofta är fria att röra sig relativt patientens skelett och yttre kontur, och många bildregistreringsalgoritmer tar hänsyn till hela bildvolymen. Arbetet som presenteras i denna avhandling syftar till att undersöka möjligheterna med arbetsflöden som baseras helt på MR data utan bildregistrering, samt arbetsflöden som använder bildregistrerings-algoritmer som är bättre anpassade för tumörer som kan röra sig i förhållande till patientens övriga anatomi, som till exempel prostatacancer.

Positron emission tomography (PET) is a molecular imaging technique that provides a direct and accurate evaluation of tissue function in vivo. PET of the glucose analogue 18F-fluoro-deoxy-glucose, is increasingly in use to aid in gross target volume delineation in radiotherapy treatment planning (RTP) where it shows reduced inter-observer variability. The aim of this thesis was to develop and investigate a new technique for delineating PET-GTV with sufficient accuracy for RTP. A new technique, volume and contrast adjusted thresholding (VCAT), has been developed to automatically determine the optimum threshold value that measures the true volume on PET images. The accuracy was investigated in spherical and irregular lesions in phantoms using both iterative and filtered back-projection reconstructions and different image noise levels. The accuracy of delineation for the irregular lesions was assessed by comparison with CT using the Dice Similarity Coefficient and Euclidean Distance Transformation. A preliminarily investigation of implementing the newly developed technique in patients was carried out. VCAT proved to determine volumes and delineate tumour boundaries on PET/CT well within the acceptable errors for radiotherapy treatment planning irrespective of lesion contrast, image noise level and reconstruction technique.

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No description available.

Objectives: The purpose of this study was to evaluate whether differences exist in: (1) orthodontists’ aesthetic analysis of treatment need from profile and frontal view photos of the same patient; (2) orthodontists’ proposed treatment type and their aesthetic analysis of treatment need from the frontal view, and (3) orthodontists’ treatment plans when given a frontal photo versus no frontal photo. A survey questionnaire was designed to test the utility of the frontal view in orthodontic treatment planning. Materials And Methods: The survey was dispersed through the Schulman Orthodontic Group utilizing SurveyMonkey. Part 1 of the survey implemented a Likert scale rating of the aesthetics of 5 patients’ frontal and profile photos. In part 2, SurveyMonkey randomly allocated participants into two groups. Survey-takers could proceed through any of the 20 customized pathways of the survey depending on their proposed treatment plans. Groups 1 and 2 were presented the same example patients; Group 1 was presented all diagnostic information and asked to formulate a treatment plan and Group 2 was given all diagnostic information minus the frontal view and asked to formulate a treatment plan, and subsequently presented with the frontal view photos to determine whether the newly revealed diagnostics changed their proposed treatment. Results: Data collection included seventy-three completed surveys from the Schulman Group composed of 140 orthodontists. A paired sample T-Test revealed significant differences in orthodontists’ analyses of need for treatment based on facial aesthetics from the frontal and profile view in all patients (p≤0.05). A Kruskal-Wallis non-parametric ANOVA test revealed no differences in proposed treatment type and orthodontists’ assessment of need for treatment based on facial view photos (p>0.05). A chi-squared analysis revealed no differences exist between treatment type proposed when a frontal view photo was provided versus not provided in 3 of 5 patients (p>0.05). Conclusion: Despite being heavily weighted from an aesthetic analysis of treatment need, the frontal view photo failed to affect significant differences in proposed treatment intervention and type. A stronger emphasis should be placed on information gained from the frontal view photos such as smile arc, buccal corridors, and incisor display, which are not being adequately considered in orthodontic treatment planning. / Oral Biology

Irreversible electroporation (IRE) is a non-thermal ablation technique that allows for eradication of unresectable tumors in a minimally invasive procedure. While IRE will preferentially kill larger cells over smaller ones, it does not discriminate between cells with larger and small nuclei. Given that one of the hallmarks of cancer cell morphology is larger, more abundant nuclei, our team set out to explore the possibility of preferentially targeting this physical and geometrical characteristic. / Master of Science