No description available.

O tratamento utilizando Radioterapia em Arco Modulado Volumétrico é a modalidade mais moderna de radioterapia conformacional de forma que, com superposição de vários campos, as distribuições de dose forneçam uma perfeita conformação ao tumor, diminuindo a probabilidade de complicações nos tecidos normais adjacentes. Nesse sentido, muitos esforços estão sendo investidos para melhorar a conformidade de distribuição de dose, bem como a integração de técnicas de imagem para rastreamento de tumores e correção de variações inter e intrafração. Para isso, um intenso acompanhamento da qualidade dos processos e um programa de garantia de qualidade são fundamentais para a segurança dos pacientes e o cumprimento da legislação vigente; além do uso de diferentes metodologias de dosimetria para inter comparação e validação dos resultados. Este trabalho tem por objetivo avaliar e comparar o desempenho dos dosímetros OSL de óxido de alumínio (Al2O3:C) fabricados pela Landauer Inc. com os fabricados pela Rexon™ na dosimetria de feixes clínicos de fótons de energias altas empregados em radioterapia com tratamento em arco modulado volumétrico (VMAT) utilizando diferentes objetos simuladores. Os dosímetros foram caracterizados para radiação gama do 60Co e para feixes clínicos de fótons de 6 MV típicos de tratamentos por VMAT em condições de equilíbrio eletrônico e de dose máxima respectivamente. Testes de desempenho das leitoras TL e OSL utilizadas e repetibilidade das amostras foram avaliadas. Após realizados todos os testes, os dosímetros foram irradiados na simulação de diferentes tratamentos radioterápicos por VMAT e suas respostas comparadas ao sistema de planejamento. Todos os tipos de dosímetros apresentaram resultados satisfatórios na verificação das doses desse tipo de simulação de planejamento. Os dosímetros de Al2O3:C apresentaram resultados compatíveis entre si e validados pelos outros dosímetros e câmara de ionização. Em relação a melhor técnica, o sistema comercial OSL InLight apresenta maior praticidade e versatilidade para uso e aplicação na rotina clínica. / Treatment using Volumetric Modulated Arc Radiation Therapy is the most modern modality of conformational radiotherapy so that, with the overlapping of several fields, the dose distributions provide a perfect conformation to the tumor, reducing the probability of complications in adjacent normal tissues. In this sense, many efforts are being invested to improve dose distribution compliance as well as the integration of imaging techniques for tumor screening and correction of inter and intrafraction variations. To this end, an intensive monitoring of the quality of the processes and a quality assurance program are fundamental for patient safety and compliance with current legislation; besides the use of different dosimetry methodologies for intercomparison and validation of the results. The aim of this study is to evaluate and compare the performance of aluminum oxide (Al2O3:C) OSL dosimeters manufactured by Landauer Inc. with those produced by Rexon™ in the dosimetry of high energy photon clinical bundles used in arcuate treatment Modulated volumetric (VMAT) using different simulating objects. The dosimeters were characterized for gamma radiation of the 60Co and for clinical photon beams of 6 MV typical of treatments by VMAT under conditions of electronic equilibrium and maximum dose respectively. Performance tests of the TL and OSL readers used and repeatability of the samples were evaluated. After all tests, the dosimeters were irradiated in the simulation of different radiotherapy treatments by VMAT and their responses compared to the planning system. All types of dosimeters presented satisfactory results in verifying the doses of this type of planning simulation. The Al2O3:C dosimeters presented compatible results and validated by the other dosimeters and ionization chamber. Regarding the best technique, the OSL InLight commercial system presents greater practicality and versatility for use and application in the clinical routine.

Les nouvelles techniques de la radiothérapie (Stéréotaxie, IMRT, VMAT, IGRT...etc) utilisent des faisceaux de photons de très petite taille (mini-faisceaux) dans le cas de petite tumeur, au cerveau par exemple, afin d'irradier précisément la lésion. En effet, leur taille de champ est inférieure à 3cm×3cm à 100 cm de la source de rayonnement, cependant la mesure de la dose dans les mini-faisceaux est caractérisée par de forts gradients de dose et un manque d'équilibre électronique latéral, nécessitant l'utilisation de détecteurs ayant un volume sensible et une résolution spatiale adaptés, avec une équivalence-eau aussi bonne que possible afin d'améliorer la précision de la dose mesurée. Les détecteurs commercialisés ne remplissent parfaitement ces conditions. Actuellement, il n'existe pas de consensus méthodologique international, ni de référence métrologique pour mesurer la dose dans les mini-faisceaux. Le protocole IAEA 398 utilisé pour calculer la dose absorbée dans un faisceau de 10×10 cm², n'est plus approprié pour les mini-faisceaux. Ce travail compare la mesure des données dosimétriques par différents détecteurs conçus pour ce type de faisceau et optimise celui le plus proche de la réalité. En absconse de référence métrologique, la vérification de l'ensemble de la mesure des données dosimétriques est assurée par l'utilisation des films gafchromiques du fait de son excellente résolution spatiale. Cette étude propose une méthode expérimentale pour estimer la dose délivrée en stéréotaxie intracrânienne. Cette méthode est basée sur la mesure de la dose de fuite en un point situé en dehors du champ d'irradiation. / The advanced techniques of radiotherapy use very small fields in case small tumors such as in the brain to irradiate precisely the lesion. This work concerns the measurement absorbed dose in small field of 0.5×0.5cm² to 3×3cm². However, the measurement dose in small fields is characterized by high gradient dose and a leak of lateral electronic equilibrium. That requires use a detector having an adapted sensitive volume and adapted spatial resolution. The detectors marketed are not perfectly compatible with these conditions. Actually, there is no international methodological consensus, nor a metrological reference for measurement dose in small fields. The IAEA (International Atomic Energy Agency) protocol 398 used to calculate the absorbed dose at 10cm×10cm isn't suitable for small fields. In absence a referenced detector, the dosimetric data measurement is verified using a Gafcromic films due to its excellent spatial resolution. We measure using conventional detectors (ionization chambers and/or Gafcromic film) the leakage dose at a point outside of irradiated field. The dosimetric data such as output factor OF, depth PDD percentage depth dose and dose profile OAR were also carried out by the diode. The correlation between the on-axis dose and off-axis dose is the subject of our study. This study proposes an experimental method to calculate the on-axis dose in small field for stereotactic radiotherapy. The method is based on the out of field leakage measurement. This model can be used to validate dose and output factor measurement. The experimental validation of the present method was performed for square and rectangular fields with sizes ranging from 0.5cm×0.5cm to 10cm×10cm.

O tratamento utilizando Radioterapia em Arco Modulado Volumétrico é a modalidade mais moderna de radioterapia conformacional de forma que, com superposição de vários campos, as distribuições de dose forneçam uma perfeita conformação ao tumor, diminuindo a probabilidade de complicações nos tecidos normais adjacentes. Nesse sentido, muitos esforços estão sendo investidos para melhorar a conformidade de distribuição de dose, bem como a integração de técnicas de imagem para rastreamento de tumores e correção de variações inter e intrafração. Para isso, um intenso acompanhamento da qualidade dos processos e um programa de garantia de qualidade são fundamentais para a segurança dos pacientes e o cumprimento da legislação vigente; além do uso de diferentes metodologias de dosimetria para inter comparação e validação dos resultados. Este trabalho tem por objetivo avaliar e comparar o desempenho dos dosímetros OSL de óxido de alumínio (Al2O3:C) fabricados pela Landauer Inc. com os fabricados pela Rexon™ na dosimetria de feixes clínicos de fótons de energias altas empregados em radioterapia com tratamento em arco modulado volumétrico (VMAT) utilizando diferentes objetos simuladores. Os dosímetros foram caracterizados para radiação gama do 60Co e para feixes clínicos de fótons de 6 MV típicos de tratamentos por VMAT em condições de equilíbrio eletrônico e de dose máxima respectivamente. Testes de desempenho das leitoras TL e OSL utilizadas e repetibilidade das amostras foram avaliadas. Após realizados todos os testes, os dosímetros foram irradiados na simulação de diferentes tratamentos radioterápicos por VMAT e suas respostas comparadas ao sistema de planejamento. Todos os tipos de dosímetros apresentaram resultados satisfatórios na verificação das doses desse tipo de simulação de planejamento. Os dosímetros de Al2O3:C apresentaram resultados compatíveis entre si e validados pelos outros dosímetros e câmara de ionização. Em relação a melhor técnica, o sistema comercial OSL InLight apresenta maior praticidade e versatilidade para uso e aplicação na rotina clínica. / Treatment using Volumetric Modulated Arc Radiation Therapy is the most modern modality of conformational radiotherapy so that, with the overlapping of several fields, the dose distributions provide a perfect conformation to the tumor, reducing the probability of complications in adjacent normal tissues. In this sense, many efforts are being invested to improve dose distribution compliance as well as the integration of imaging techniques for tumor screening and correction of inter and intrafraction variations. To this end, an intensive monitoring of the quality of the processes and a quality assurance program are fundamental for patient safety and compliance with current legislation; besides the use of different dosimetry methodologies for intercomparison and validation of the results. The aim of this study is to evaluate and compare the performance of aluminum oxide (Al2O3:C) OSL dosimeters manufactured by Landauer Inc. with those produced by Rexon™ in the dosimetry of high energy photon clinical bundles used in arcuate treatment Modulated volumetric (VMAT) using different simulating objects. The dosimeters were characterized for gamma radiation of the 60Co and for clinical photon beams of 6 MV typical of treatments by VMAT under conditions of electronic equilibrium and maximum dose respectively. Performance tests of the TL and OSL readers used and repeatability of the samples were evaluated. After all tests, the dosimeters were irradiated in the simulation of different radiotherapy treatments by VMAT and their responses compared to the planning system. All types of dosimeters presented satisfactory results in verifying the doses of this type of planning simulation. The Al2O3:C dosimeters presented compatible results and validated by the other dosimeters and ionization chamber. Regarding the best technique, the OSL InLight commercial system presents greater practicality and versatility for use and application in the clinical routine.

<p>Enterochromaffin-like (ECL) and ghrelin cells, in the human gastric mucosa and in gastric endocrine tumours (GETs), were subclassified with respect to immunohistochemical reaction <i>vs.</i> vesicular monoamine transporter 2 (VMAT-2), ghrelin/obestatin, and histidine decarboxylase (HDC). The immunohistochemical expression of ghrelin/obestatin and HDC in GETs was related/correlated to plasma ghrelin/obestatin and urinary methyl imidazole acetic acid (U-MeImAA) excretion respectively, with the intention of identifying markers for these tumour types. </p><p>ECL cells in the gastric mucosa appear either with VMAT-2 only, or with HDC immunoreactivity only, or they can express both proteins; but in GETs the transporter protein and the enzyme were almost always co-expressed in the same cells. Furthermore, ghrelin and obestatin were co-localized in the same cells in the gastric mucosa and in the tumours. In the gastric mucosa, occasional ghrelin/obestatin cells expressed VMAT-2, but in GETs these proteins were always co-localized. Ghrelin expressing cells were non-immunoreactive to HDC. Plasma ghrelin/obestatin concentrations remained low in patients with GETs, irrespective of the relative incidence of these cells in the mucosa and in tumours. The plasma values were not related/correlated to various clinico-pathological parameters. A malignant ghrelinoma was however an exception. The tumour released high total and active ghrelin concentrations into the blood circulation. The patient suffered from diarrhoea, hypothyroidism and diabetes mellitus, but it is not clear if these conditions were due to hyperghrelinaemia. The excretion U-MeImAA was increased in a few patients with GETs, but this increase was not always related to clinical symptoms.</p><p>In conclusion, ECL cells are an heterogeneous group according to VMAT-2 and HDC immunoreactivity. Ghrelin and obestatin are expressed in the same cells in the gastric mucosa, and a few of these cells display VMAT-2 immunoreactivity. Ghrelinoma is a new gastric tumour entity.</p>

Enterochromaffin-like (ECL) and ghrelin cells, in the human gastric mucosa and in gastric endocrine tumours (GETs), were subclassified with respect to immunohistochemical reaction vs. vesicular monoamine transporter 2 (VMAT-2), ghrelin/obestatin, and histidine decarboxylase (HDC). The immunohistochemical expression of ghrelin/obestatin and HDC in GETs was related/correlated to plasma ghrelin/obestatin and urinary methyl imidazole acetic acid (U-MeImAA) excretion respectively, with the intention of identifying markers for these tumour types. ECL cells in the gastric mucosa appear either with VMAT-2 only, or with HDC immunoreactivity only, or they can express both proteins; but in GETs the transporter protein and the enzyme were almost always co-expressed in the same cells. Furthermore, ghrelin and obestatin were co-localized in the same cells in the gastric mucosa and in the tumours. In the gastric mucosa, occasional ghrelin/obestatin cells expressed VMAT-2, but in GETs these proteins were always co-localized. Ghrelin expressing cells were non-immunoreactive to HDC. Plasma ghrelin/obestatin concentrations remained low in patients with GETs, irrespective of the relative incidence of these cells in the mucosa and in tumours. The plasma values were not related/correlated to various clinico-pathological parameters. A malignant ghrelinoma was however an exception. The tumour released high total and active ghrelin concentrations into the blood circulation. The patient suffered from diarrhoea, hypothyroidism and diabetes mellitus, but it is not clear if these conditions were due to hyperghrelinaemia. The excretion U-MeImAA was increased in a few patients with GETs, but this increase was not always related to clinical symptoms. In conclusion, ECL cells are an heterogeneous group according to VMAT-2 and HDC immunoreactivity. Ghrelin and obestatin are expressed in the same cells in the gastric mucosa, and a few of these cells display VMAT-2 immunoreactivity. Ghrelinoma is a new gastric tumour entity.

Purpose: At the Wellington Blood and Cancer Centre (WBCC), Volumetric Modulated Arc Therapy (VMAT) is used to treat a variety of head and neck (H&N) cancers. Presently, the complexity of plans is limited to ensure the accuracy of patient treatment within the range of the departmental experience. The complexity limitation is applied through use of a monitor unit (MU) constraint during plan optimisation. Plans of higher complexity can be obtained by loosening the MU constraint, and setting more stringent optimisation objectives on organs at risk (OAR) and target volumes (PTV). This could potentially yield higher quality treatment plans but may also degrade the accuracy of the TPS calculation or the plan delivery at the treatment machine. The aim of this study is to investigate the level of plan complexity that results in accurate treatment plan calculation and delivery, and quantify the corresponding gain in plan quality. Methods: Five previously treated H&N patients were selected for the study. Each patient’s clinical plan was used as the lowest complexity level and labelled C1. Subsequently, an approximate pareto-optimal plan (C3) was created that focused equally on sparing spinal cord, brain stem and parotid gland while maintaining, or improving on, the previously obtained target coverage. Next, a C2 plan was created such that the plan quality was in between C1 and C3. Plan quality of each complexity level was assessed in terms of OAR sparing and PTV coverage. The average leaf pair opening (LPO), critical leaf pair opening (%LPO<1cm) and mean leaf travel were used as plan complexity metrics. The calculation and delivery accuracy of each complexity level using Varian TrueBeam LINAC/Eclipse TPS was verified using time resolved point dose measurements (TRPD), EBT film measurements (Ashland Inc.) and ArcCheck measurements (Sun Nuclear Corp.). A comprehensive uncertainty analysis was carried out including a quantification of the measurement and delivery reproducibility. Results: Increasing plan complexity from C1 to C3 reduced the Spinal Cord D1cc, Brain Stem D1 and Parotid Gland Dmean up to 14.7 Gy, 7.1 Gy and 7.8 Gy, respectively. In addition, C3 plans improved the target coverage compared to C1 plans, with the PTV66 and PTV54 D98 increasing up to 1.0 Gy and 0.6 Gy, respectively. The verification measurements showed that the plan calculation and delivery for all complexity levels was well within clinical acceptance levels (Table 1). TRPD showed that VMAT dose delivery itself was repeatable within 0.1% (1 S.D.) over 10 consecutive deliveries for both C1 and C3 complexity levels. Discussion & Conclusions: This study has shown that increasing the plan complexity can provide significant dosimetric advantages for the treatment of H&N cancer. Verification measurement results indicated that this did not noticeably degrade the calculation and delivery accuracy of VMAT using a Varian TrueBeam LINAC and our Eclipse TPS beam model. H&N VMAT at the WBCC can now be developed further with greater confidence in the dosimetric accuracy of higher complexity plans.

La technique de radiothérapie VMAT (Volumetric Modulated Arc Therapy), diffusée en 2009, combine les avantages des techniques d'arc thérapie dynamique aux avantages des techniques de radiothérapie conformationnelle avec modulation d'intensité (RCMI) par faisceaux stationnaires. L'objectif de la thèse est de rendre optimales les conditions de mise en œuvre du VMAT autour d'un accélérateur linéaire d'électrons Synergy/Elekta afin de sécuriser la technique et de pouvoir bénéficier de l'apport clinique potentiellement attendu. Sur la base d'une analyse de l'influence des différents paramètres de la chaîne de traitement, nous proposons des éléments d'optimisation du traitement à la fois sur la planification dosimétrique et sur le contrôle de son exécution sur la machine. Nous montrons que si la qualité de l'optimisation de la technique dépend des caractéristiques intrinsèques de l'accélérateur, elle est également fortement influencée par le paramétrage du système de planification des traitements (TPS). Nous mettons en évidence des différences comparées des collimateurs Beam Modulateur (largeur de lames de 4 mm) et MLCi2 (largeur de lames de 10 mm) tant sur le plan de la distribution de dose obtenue que sur l'efficience. Nous montrons que, si pour deux principaux TPS commercialisés (Pinnacle/Philips et Monaco/Elekta) les distributions de dose aux volumes cibles sont peu modifiées, les différences de méthodes implémentées influencent la distribution de dose aux tissus sains. Nous proposons des programmes de contrôles de qualité au niveau de l'accélérateur, des plans dosimétriques de traitement et de l'exécution des traitements. Afin de garantir un niveau de confiance élevé sur la dose délivrée, nous proposons une méthode d'évaluation de la fluence délivrée en cours de traitement basée sur l'analyse des paramètres machines. Nous établissons que le processus de traitement VMAT optimisé fournit des performances de qualité supérieure que les techniques de RCMI par faisceaux stationnaires pour quatre localisations tumorales majeures étudiées.

La technique de radiothérapie VMAT (Volumetric Modulated Arc Therapy), diffusée en 2009, combine les avantages des techniques d'arc thérapie dynamique aux avantages des techniques de radiothérapie conformationnelle avec modulation d'intensité (RCMI) par faisceaux stationnaires. L'objectif de la thèse est de rendre optimales les conditions de mise en œuvre du VMAT autour d'un accélérateur linéaire d'électrons Synergy/Elekta afin de sécuriser la technique et de pouvoir bénéficier de l'apport clinique potentiellement attendu. Sur la base d'une analyse de l'influence des différents paramètres de la chaîne de traitement, nous proposons des éléments d'optimisation du traitement à la fois sur la planification dosimétrique et sur le contrôle de son exécution sur la machine. Nous montrons que si la qualité de l'optimisation de la technique dépend des caractéristiques intrinsèques de l'accélérateur, elle est également fortement influencée par le paramétrage du système de planification des traitements (TPS). Nous mettons en évidence des différences comparées des collimateurs Beam Modulateur (largeur de lames de 4 mm) et MLCi2 (largeur de lames de 10 mm) tant sur le plan de la distribution de dose obtenue que sur l'efficience. Nous montrons que, si pour deux principaux TPS commercialisés (Pinnacle/Philips et Monaco/Elekta) les distributions de dose aux volumes cibles sont peu modifiées, les différences de méthodes implémentées influencent la distribution de dose aux tissus sains. Nous proposons des programmes de contrôles de qualité au niveau de l'accélérateur, des plans dosimétriques de traitement et de l'exécution des traitements. Afin de garantir un niveau de confiance élevé sur la dose délivrée, nous proposons une méthode d'évaluation de la fluence délivrée en cours de traitement basée sur l'analyse des paramètres machines. Nous établissons que le processus de traitement VMAT optimisé fournit des performances de qualité supérieure que les techniques de RCMI par faisceaux stationnaires pour quatre localisations tumorales majeures étudiées.

A technique for the in vivo dose verification of intensity modulated radiation therapy (IMRT) has been developed. An electronic portal image, calibrated in terms of absolute dose, is acquired for each radiation field following transmission through the patient at the time of treatment. For an IMRT field, the portal image signal is back-projected through a model of the patient in order to calculate the dose at the isocentric plane perpendicular to the beam central axis. The IMRT in vivo dose verification technique was adapted for volumetric modu- lated arc therapy (VMAT) treatments when a single dosimetric image is acquired over an arc. The patient dose along axis of gantry rotation can be directly related to the signal along the vertical axis of EPIs in integrated mode. In this novel VMAT in vivo dosimetry technique, the portal image signal is back-projected through a rotationally averaged model of the patient to calculate a 1D in vivo dose along the axis of gantry rotation. A research ethics board clinical study was approved and transmission portal images were acquired at regular intervals from human subjects. Portal image-derived isocenter point doses were in good agreement with treatment planning system (TPS) calculations for IMRT (mean difference δ=0.0%, standard deviation of the differences σ=4.3%) and VMAT (δ=1.1%, σ=1.7%). The one-dimensional (VMAT) and two-dimensional (IMRT) reconstructed doses were further analyzed by calculating mean dose differences and γ−evaluation pass-rates, which were also shown to be in good agreement with TPS calculations. The portal image-based in vivo dosimetry techniques were shown to be clinically feasible, with reconstruction times on the order of minutes for the first fraction and less than one minute for each fraction thereafter. / Graduate / 0760 / 0574 / 0760