The goal of this work is to develop an accurate and automatic tool to evaluate normal lung tissue response to radiotherapy (RT) and its correlation with local dose. Manifestation of radiation-induced lung disease (RILD)in radiography is a measurable endpoint for RT-induced normal tissue complication. Follow-up CT images from RT-received non-small-cell lung cancer patients were registered to a corresponding planning CT image. Followingimage intensity calibration, the extent of RILD was segmented based on the change in physical density during the follow-up period. Dose coverage to the RILD segmentation and healthy lung was calculated based on retrievedtreatment plans. Normal tissue response in terms of RILD volume and local dose-response showed dependency on patients and follow-up periods. Monte-Carlo dose calculation was found to be important to obtain bettercorrelation. Provided the improved accuracy in CT calibration and image registration, this tool can facilitate further normal tissue toxicity studies. / Le but de ce travail est de développer un outil automatisé de haute précision permettant d'evaluer la réponse de tissus de poumons sains à la radiothérapie (RT), ainsi que leurs corrélation avec la dose locale. Les complications de tissus de poumons sains induites par RT peuvent être mesurées à l'aide des manifestations de maladies pulmonaires induites par radiations (MPIR) en radiographie. Le suivi des images CT par des cellules de poumons cancéreuses provenant de la RT a été enregistré à leur image CT de planication correspondante. à l'aide du suivi de la calibration de l'intensité de l'image, l'etendue des MPIR a été segmentée en se basant sur le changement de densité physique durant la période de suivi. La dose reliée à la segmentation des MPIR et aux tissus de poumons sains a été calculée en se basant sur des planications de traitements établis. La réponse des tissus sains en termes de volume MPIR et la réponse de la dose locale ont démontrées une dépendance signicative par rapport aux patients et aux périodes de suivi. Le calcul de dose par simulations Monte-Carlo sest révélé être important an d'obtenir de meilleures corrélations. En tenant compte de l'amélioration de l'exactitude des calibrations CT et des enregistrements d'image, cet outil peut faciliter le déroulement des futures études de toxicité des tissus sains.

In using the internal landmark matching technique for registering brain volumes from single photon emission computed tomography (SPECT) and magnetic resonance (MR) imaging, the resulting errors are different from similar registrations of positron emission tomography (PET) and MR volumes because of the anisotropic nature of SPECT's tomographic resolution. SPECT/MR registration errors are investigated with point simulation to allow a controlled study of the dependence of the translation and rotation errors on different factors. These factors include: the number of point pairs, m, the error in point pair homology (characterised by the FWHM of a 3-D Gaussian error envelope), and the configuration of the point sets (as they depend on their radius from their centroid). The results of this study are used to interpret the results from studies based on a 3-D brain phantom fitted with external fiducials to provide the basis for true registrations. / It is found that the same error distributions may not be expected across ordinates. Based on the imaging capabilities of the sensors used in this study, (a) maximum translation errors or $ pm$2.1 mm in the anterior-posterior orientation are found to be a consequence of SPECT's anisotropic resolution and the brain's major axis in that orientation, and (b) rotation errors of about $ pm$2.1$ sp circ$ in the coronal plane are larger than in the transaxial because of the comparative dimensions in those planes.

No description available.

In this thesis, physical and biological aspects of three linear-accelerator-based stereotactic radiosurgery techniques, namely the dynamic rotation, static conformal beam, and intensity-modulated beam, are compared. Comparisons are carried out using simulated targets which include spheres, hemispheres and a C-shaped target wrapped around a critical structure, inserted within modified slabs of an Alderson Rando anthropomorphic phantom. The phantom is CT-scanned with a stereotactic frame, and the images are transferred to the treatment planning systems. The best possible treatment plans are generated for each simulated target and for each of the three techniques. Treatment plans are compared using both physical (homogeneity and conformity indices) and biological parameters (integral biologically effective dose, tumour control probability and normal tissue complication probability). Possible correlation between physical and biological parameters is investigated for the three techniques. Finally, some experiments are performed to explain the lack of correlation obtained when multiple isocenters are employed in the dynamic rotation technique for the treatment of irregular targets.

Cone beam computed tomography (CBCT) is a recent development in radiotherapy for use in image guidance. Image guided radiotherapy using CBCT allows visualization of soft tissue targets and critical structures prior to treatment. Dose escalation is made possible by accurately localizing the target volume while reducing normal tissue toxicity. The kilovoltage x-rays of the cone beam imaging system contribute additional dose to the patient. In this study a 2D reference radiochromic film dosimetry method employing GAFCHROMICTM model XR-QA film is used to measure point skin doses and dose profiles from the Elekta XVI CBCT system integrated onto the Synergy linac. The soft tissue contrast of the daily CBCT images makes adaptive radiotherapy possible in the clinic. In order to track dose to the patient or utilize on-line replanning for adaptive radiotherapy the CBCT images must be used to calculate dose. A Hounsfield unit calibration method for scatter correction is investigated for heterogeneity corrected dose calculation in CBCT images. Three Hounsfield unit to density calibration tables are used for each of four cases including patients and an anthropomorphic phantom, and the calculated dose from each is compared to results from the clinical standard fan beam CT. The dose from the scan acquisition is reported and the effect of scan geometry and total output of the x-ray tube on dose magnitude and distribution is shown. The ability to calculate dose with CBCT is shown to improve with the use of patient specific density tables for scatter correction, and for high beam energies the calculated dose agreement is within 1%. / La tomographie par faisceaux conique (CBCT) informatisée a été récemment développée en radiothérapie pour l'utilisation de guidage par imagerie. La radiothérapie guidée par imagerie (IGRT) utilisant le CBCT, permet la visualisation des cibles à tissus mous et des structures critiques avant le traitement. En localisant précisément la cible, une « escalade » de dose est rendue possible et la toxicité des tissus sains est réduite. Les rayons-X à basse énergie (kilovoltage) du system d'imagerie du CBCT, contribue à une dose additionnelle pour le patient. Dans cette étude, une méthode dosimétrique utilisant un film 2D radiochromic (Gafchromic film, model XR-QA) a été employé pour mesurer des points de dose à la peau ainsi que des profiles de dose. Cette étude a été réalisée à l'aide d'un system d'Elekta XVI CBCT installé sur un accélérateur linéaire du Synergy. Le contraste des images quotidiennes du CBCT des tissus mous rend possible au niveau clinique l'utilisation de la radiothérapie adaptive. Dans le but de suivre la dose administrée au patient ou utiliser de la replanification en ligne pour la radiothérapie adaptive, les images CBCT doivent être utilisées pour le calcul de dose. Une calibration des unités de Hounsfield par méthode de correction de dispersion est examinée dans le cas de dose calculée dans des milieux hétérogènes pour les images CBCT. Trois unités de Hounsfield par table de calibration de densité sont utilisées pour chaque des quatre cas incluant des patients et un fantôme anthropomorphique. Le calcul de dose pour chaque cas est comparé avec les résultats cliniques standards de tomographie par faisceaux en éventail. La dose acquise avec le scanner est reportée et l'effet géométrique du scanner ainsi que le débit total du tube a rayon-X sur la magnitude et la distribution de la dose sont montrés. La capacité de calculer la dose avec un CBCT est présentée dans le but d'amélio

The DICOM-conformant PACS of the MGH was subjected to a performance study. The goal was to develop the tools needed to extract meaningful, quantitative measures related to performance with a view towards establishing reliable indicators that can help identify design weaknesses and performance changes over time. Efforts focused on operational scenarios such as moving images from servers to workstations, automatic routing and prefetching tasks. The performance of each process underlying these scenarios was studied using residency timing combined with a web-based monitoring system to yield quantitative data from various low-level resources on each server. While the critical processes and hardware on the PACS were already monitored to identify faults, the tools developed in this study now provide the means to assess overall performance issues. The results have yielded insights that have helped to identify faulty and inefficient logic in certain program constructs, and suggestions for design improvement and software enhancement. / Le PACS du HGM a été soumis à des études de performance. Le but était de développer des outils qui permettent d’obtenir des mesures quantitatives reliées aux performances, afin d’établir des indicateurs fiables permettant d’identifier des points faibles du design et des variations des performances. Les efforts ont été concentrés sur des scénarios opérationnels tels que le transfer d’images des serveurs aux stations de travail, et les services automatisés de distribution d’images. La performance de chacun des procédés utilisés pour ces scénarios a été étudié en utilisant le temps de résidence combiné avec un outils de surveillance du système qui permet ainsi l’acquisition de données quantitatives pour plusieurs ressources de base de chacun des serveurs. Bien que les principaux programmes, ainsi que les équipements du PACS, soient déjà sous surveillance, les outils developpés dans cette étude permettent d’évaluer les problèmes de performance global. Les résultats ont aidé à identifier des erreurs et des inneficacités dans les algorithmes de certains programmes, et ont permis de suggérer des améliorations au design ainsi qu’aux programmes. fr

<p>Dynamic contrast-enhanced (DCE) MRI has been widely used as a quantitative imaging method for monitoring tumor response to therapy. The pharmacokinetic parameters derived from this technique have been used in more than 100 phase I trials and investigator led studies. The simultaneous challenges of increasing the temporal and spatial resolution, in a setting where the signal from the much smaller voxel is weaker, have made this MR technique difficult to implement in small-animal imaging. Existing preclinical DCE-MRI protocols acquire a limited number of slices resulting in potentially lost information in the third dimension. Furthermore, drug efficacy studies measuring the effect of an anti-angiogenic treatment, often compare the derived biomarkers on manually selected tumor regions or over the entire volume. These measurements include domains where the interpretation of the biomarkers may be unclear (such as in necrotic areas).</p><p>This dissertation describes and compares a family of four-dimensional (3D spatial + time), projection acquisition, keyhole-sampling strategies that support high spatial and temporal resolution. An interleaved 3D radial trajectory with a quasi-uniform distribution of points in k-space was used for sampling temporally resolved datasets. These volumes were reconstructed with three different k-space filters encompassing a range of possible keyhole strategies. The effect of k-space filtering on spatial and temporal resolution was studied in phantoms and in vivo. The statistical variation of the DCE-MRI measurement is analyzed by considering the fundamental sources of error in the MR signal intensity acquired with the spoiled gradient-echo (SPGR) pulse sequence. Finally, the technique was applied for measuring the extent of the opening of the blood-brain barrier in a mouse model of pediatric glioma and for identifying regions of therapeutic effect in a model of colorectal adenocarcinoma. </p><p>It is shown that 4D radial keyhole imaging does not degrade the system spatial and temporal resolution at a cost of 20-40% decrease in SNR. The time-dependent concentration of the contrast agent measured in vivo is within the theoretically predicted limits. The uncertainty in measuring the pharmacokinetic parameters with the sequences is of the same order, but always higher than, the uncertainty in measuring the pre-injection longitudinal relaxation time. The histogram of the time-to-peak provides useful knowledge about the spatial distribution of K^trans and microvascular density. Two regions with distinct kinetic parameters were identified when the TTP map from DCE-MRM was thresholded at 1000 sec. The effect of bevacizumab, as measured by a decrease in K^trans, was confined to one of these regions. DCE-MRI studies may contribute unique insights into the response of the tumor microenvironment to therapy.</p> / Dissertation

In this thesis, a detailed review and analysis is undertaken of the numerical and theoretical data employed in the various National and International Dosimetry Protocols and Codes of Practice currently in use. Air kerma to dose conversion factors for megavoltage photon and electron beams are then derived, using each of the protocols, for a variety of commonly used ionisation chambers and it is found that differences in the resultant values are present for both photon and electron beams. For example, for a NE2571 graphite walled cylindrical ionisation chamber, the maximum variation in the air kerma to dose conversion factor for photons <I>C_w,λ</I> occurs at a "nominal" energy of 25MV, where the difference between the maximum and minimum values of <I>C_w,λ</I>is 5.1%, while the maximum difference between the different protocols in the air kerma to dose conversion factor for electrons <I>C_w,e</I>occurs at a mean incident energy of 9 MeV, where the difference between the maximum and minimum values of <I>C_w,e</I> is 2.7%. Analysis of the conversion factors indicates that the cause of these differences is due to a combination of both the numerical data and theoretical factors employed, although the major contributions to the differences arise from the use of different sets of stopping power ratios in the different protocols; in turn the use of different sets of stopping power ratios arises partly from different methods of specifying beam quality. An experimental approach was, therefore, developed to determine the consistency of each protocol's air kerma to dose conversion factors with an absolute value for one quality of beam, i.e. the relationship to a photon calibration standard, and also to examine the consistency between photon and electron beam modalities. When Cobalt-60 gamma rays were used as a calibration quality and comparative measurements were made in photon beams of nominal energies from 6MV to 25MV, and electron beams of nominal incident energies from 5MeV to 20MeV, inconsistencies were found in the majority of protocols and, for photon beams this was found to be attributable to inadequate description of photon beam quality.

We studied 42 rectal cancer brachytherapy patients with shielding included in the treatment, but without shielding included in the treatment planning and dose distribution calculations. To study the dose distribution in shielded cases, we first extracted relevant information from the PLATO BPS system and reconstructed the PLATO treatment plans with negligible errors. Based on this, we then implemented and validated the dose-superposition algorithm and applied this algorithm to all patients, finding that although the dose to healthy tissue is reduced, 10 of the 42 patients ended up with more than a 5% 'cold spot,' which is not acceptable in clinical practice. To solve this problem, a highly automated simulated annealing (SA) optimization algorithm, with a well-developed new cost function, was designed and implemented. The algorithm alone can decrease 'V90 to healthy tissue' by 17% while keeping the dose to target at the same level. By adding a shielding rod, the algorithm can further decrease the 'V90 to healthy tissue' by an additional 13%. The average calculation time for a patient using the dose-superposition algorithm was less than 20 seconds, and the time needed to make an SA based treatment plan for a shielded case was less than 10 minutes. The SA algorithm is independent of the physicist's experience. Two simplified algorithms for dose distribution calculation were investigated, the TG43 analytical shielding algorithm and the PLATO shielding algorithm. Their calculated results show conformal isodose lines to that from the dose-kernel-superposition algorithm, but present less accuracy and precision and much longer calculation times. Hence they are useful in limited conditions. Finally, we did some preliminary investigation / Nous avons étudié 42 cas de brachythérapie de cancer rectale avec protection incluse dans le traitement mais sans protection incluse dans la planification du traitement et calcul des distributions de doses. Pour étudier la distribution des doses dans les cas protégés, nous avons prélevé des informations importantes du système PLATO BPS et rétabli les plans de traitement PLATO avec des erreurs négligeables. Sur ces bases nous avons ensuite implémenté et validé les algorithmes de superposition des doses et appliqué ces algorithmes sur tous les patients, découvrant que bien que la dose pour tissu sain a été réduite, 10 des 42 patients se sont retrouvés avec plus de 5% de 'tache froide', ce qui est inacceptable dans les pratiques cliniques. Pour résoudre ce problème, nous avons conçu et implémenté un recuit simulé (RS) hautement automatisé pour optimisation de l'algorithme avec une nouvelle fonction de coût bien développée. L'algorithme en soi peut amoindrir 'V90 à tissu sain' de 17% tout en gardant les doses à objectif au même niveau. En ajoutant une baguette de protection, l'algorithme peut encore réduire le 'V90 à tissu sain' de 13% supplémentaires. Le calcul moyen de la durée pour un patient utilisant l'algorithme de superposition de dose est de moins de 20 secondes et le temps nécessaire pour un plan de traitement à base de RS pour un cas protégé fut moins de 10 minutes. L'algorithme RS est indépendant de l'expérience du physicien. Deux algorithmes simplifiés pour le calcul des doses de distribution ont été étudiés, l'algorithme TG43 de protection analytique et l'algorithme de protection PLATO. Leurs résultats calculés montrent des lignes isodoses conformes à des algorithmes d

This thesis presents an investigation of depth doses of 9-18 MeV electron beams measured with custom-built ionization chambers, film, and TLD in homogeneous solid water and bone-like phantoms as well as in a solid-water/bone heterogeneous phantom. Our measurement results show that dosimetry based on film and TLD corresponds well with ionization chamber dosimetry in both homogeneous and heterogeneous phantoms if appropriate methods for converting film or TLD responses to doses in phantom are used. We observed no clinically significant dose enhancement in relatively thin bone heterogeneities, however, we found dose enhancement in solid homogeneous bone phantoms. Work by previous investigators might have overestimated the dose in bone heterogeneities. We also found that the coefficient equivalent thickness (CET) method is suitable for estimating of dose in heterogeneous phantoms incorporating large uniform heterogeneities. / The thesis also presents an investigation of magnitudes, energies, and dose profiles of photon contaminations for 9-18 MeV electron beams with various field sizes used clinically. Our measurements show that the magnitude of photon contamination increases both with electron beam energy and with field size. The photon contamination dose profile is forward peaked and its energy decreases with an increase in field size.