Radiation therapy, one of the most common forms of cancer treatment, is continually evolving with the introduction of new technology, more complex treatments and more advanced radiation dose calculations. To ensure the effectiveness and safety of modern radiation therapy, dose measurement tools must improve to accommodate these advances. X-ray computed tomography (CT) polymer gel dosimetry is a unique type of dosimeter that has many advantages and the potential to address some of the challenges in the verification of dose delivery and calculation in radiation therapy. This dissertation investigates the advancement of an x-ray CT polymer gel dosimetry system for use in clinical applications and in particular for deformable dose verification. The first part of this work consists of a reproducibility study of an established x-ray CT polymer gel dosimetry system in an effort to determine the accuracy and precision of dose measurements made with this system and the feasibility of interbatch and generic calibration. Gel measurements were found to have excellent agreement with Monte Carlo dose calculation when using a generic calibration curve. The excellent dosimetric and spatial accuracy established in this study suggest that this dosimetry system is ideally suited for the measurement of high-dose fractionation treatments such as stereotactic radiosurgery (SRS) or stereotactic body radiation therapy (SBRT). The second stage was the development and characterization of the first deformable x-ray CT polymer gel dosimetry system. This study established the setup reproducibility, deformation characteristics and dose response of the new deformable system. The dose response was found to be similar to that of the non-deformable system with similar dosimetric and spatial accuracy when compared to Monte Carlo dose calculation. The system was also found to have sub-millimetre setup reproducibility and the deformable dosimeter was found to reproducibly deform and relax for external compression of up to 30 mm and over 100 consecutive compressions. This work established several important characteristics of the new deformable dosimetry system and it shows excellent potential for use in the evaluation of deformable dose accumulation algorithms. The final component of this dissertation was the use of the newly developed deformable dosimetry system in the evaluation of a novel deformable dose accumulation algorithm, defDOSXYZ. Gel measurements and defDOSXYZ showed excellent agreement in the case of a static control case and this set a benchmark for deformable dose measurements. Measurements of deformed dose by the gel dosimeter showed significant disagreement with dose deformed by defDOSXYZ and the dosimetric differences were well outside the uncertainties established in the first two studies of this dissertation. The results from this study provided some insight into potential avenues of improvement for both the deformable dose calculation and deformable dose measurements. These results were also the first example of deforming dose measured by an x-ray CT read out gel dosimetry system. Overall, the results in this dissertation represent a significant advancement in x-ray CT polymer gel dosimetry and establish its suitability for several clinical applications. / Graduate / 2019-12-06

Este trabalho visa aprimorar e tornar mais precisa a utilização do dosímetro gel polimérico MAGIC-f no estudo da distribuição de dose para fonte radioativas utilizadas na terapia e diagnóstico em medicina nuclear. Para isso foram avaliados os parâmetros de leitura do gel em equipamentos de ressonância magnética e sua resposta quando comparado a resultados obtidos através da utilização do código PENELOPE de simulação Monte Carlo. Dentre as incertezas observadas no processo global da utilização do gel MAGIC-f, sua manufatura foi a que demonstrou uma maior preocupação uma vez que erro na frações de componentes químicos adicionados ocasiona grande diferença na resposta do dosímetro. A aquisição da informação dosimétrica em um equipamento de imagem por ressonância magnética demonstrou que tempos ao eco mais curtos são mais eficientes na diferenciação do sinal gerado no processo de polimerização devido a utilização de fontes de medicina nuclear do que ajustes na resolução da imagem e que a homogeneidade de campo magnético pode ocasionar grande alteração nos valores obtidos. Experimentos realizados com o gel MAGIC-f, demonstraram um baixa dependência energética e um grande dependência com a taxa de dose, dois fatores importantes em medicina, mas resultados simulados e experimentais comparativos utilizando fontes de I-131, Tc-99m e F-18, demonstraram uma grande precisão nos resultados apresentados, tornando assim o gel MAGIC-f uma excelente ferramenta na verificação volumétrica da dose absorvida na terapia com fontes de medicina nuclear. / This work aims to improve and make more accurate use of the gel dosimeter MAGIC-f polymer in the study of dose distribution for radioactive source used in therapy and diagnosis in nuclear medicine. For this, MRI parameters reading of the gel were evaluated and its response when compared to results obtained using a Monte Carlo simulation PENELOPE code. Among the uncertainties observed in the overall use of MAGIC-f gel, its manufacturing demonstrated a greater concern since error in chemical fractions added causes big difference in the response of the dosimeter. The acquisition of dosimetric equipment information in a magnetic resonance imaging showed that the shorter eco times are more efficient in differentiating the signal generated in the polymerization process due to the use of sources of nuclear medicine than image resolution changes and the homogeneity of the magnetic field can cause large difference in the results. Experiments performed with the MAGIC-f gel, demonstrated a low energy dependence and a large dependence on the dose rate, two important factors in nuclear medicine, but comparative results with simulated and experimental processes using sources of I-131, Tc-99m and F-18 showed a great accuracy in results, thus making the MAGIC-f gel an excellent tool for volumetric verification of absorbed dose therapy with sources of nuclear medicine.

In radiation therapy, gel dosimetry is used to measure radiation doses for treatment verification. Gel dosimeters have the ability to record dose information in three dimensions. The objective of this thesis was to fabricate a transparent cryogel radiochromic dosimeter with poly(vinyl alcohol) (PVA) as the gelling agent. A transparent dosimeter may be analyzed using an optical read out technique, which is desirable. PVA cryogels can be made transparent by adding dimethyl sulfoxide (DMSO). Measurements of dose response were performed and various parameters were adjusted, including: numbers of freeze-thaw cycles (FTCs); concentrations of PVA; DMSO concentration. The measured absorption coefficient increased linearly with dose up to approximately 10 Gy. The sensitivity was increased for higher PVA concentrations, larger numbers of FTCs, and less DMSO. The resulting dosimeter was stable and showed no significant dose rate or photon energy dependence. The cryogels were later formed into 5 mm thick films and used as a tool for performing in vivo dosimetry. The dose response of the radiochromic bolus was characterized by irradiating it on a flat surface at different gantry angles. The dose measured in the bolus was approximately 0.80 of the dose measured by Gafchromic film at the skin surface, taking the obliquity into account. IMRT treatments were delivered to a RANDO phantom. The radiochromic bolus was used to measure skin surface dose in two dimensions at various locations. The 0.80 factor was used to calibrate the bolus, which was then compared to an accompanying film measurement. Good agreement was observed between the measurements (>95% gamma pass rate), suggesting the radiochromic bolus may be suitable for in vivo applications. The radiochromic bolus was then used to evaluate errors associated with the breath hold technique often used with left chest wall tangential irradiation. Treatment plan incorporating the radiochromic bolus was delivered at the planned position and shifted anterior-posteriorly (A/P) up to 5 mm. Large discrepancies from the planned two dimensional skin surface distribution were observed for shifts as small as 3 mm in the A/P direction. The study demonstrated that the cryogel was sensitive to small positioning uncertainties for chest wall irradiations, potentially allowing for the detection of clinically relevant errors. Other potential formulations of PVA-based radiochromic cryogels are discussed briefly as avenues to future research projects. / Thesis / Doctor of Philosophy (PhD)

No description available.

This research aims to develop a tissue-mimicking material and produce a 3D gelatin that has density of approximately a human lung, which is in the ranges of (0.25 – 0.35) g/cm3. Tissue equivalent models are important in order to study the radiation dose planned for patients. To achieve the desired density of a human tissue, different types of gelatin were whisked for 300 seconds using a typical hand mixer. The mechanical properties of the gelatin mixtures, standard and foamed, were evaluated by applying different forces. The mechanical properties for the gels were measured using an indentation technique, which showed that the gels act as elastic materials. The mechanical properties of the foams were also evaluated. Mixtures that contained 300 bloom gelatin, glycerol, and sorbitol, were whisked for 60, 180, 300 seconds to achieve different densities evaluated by CT imaging. The density of the180 - and 300 - seconds gelatin foams were found to be 0.33 ± 0.16 and 0.33  0.052 g/cm3, respectively, which is similar to the human lung density. Finally, FXO gel sheets and the FXO foam sheets were irradiated and the radiosensitivity quantified by measuring transmission using a spectrometer. The change in the attenuation coefficient was linear with dose. / Thesis / Master of Science (MSc)

Dosimetry is a vital component of treatment planning in radiation therapy. Methods of radiation dosimetry currently include the use of: ionization chambers, thermoluminescent dosimeters (TLDs), solid-state detectors and radiographic film. However, these methods are inherently either 1D or 2D and their use involves the perturbation of the radiation beam. Although the dose distribution within tissues following radiation therapy treatments can be modeled using computerized treatment planning systems, a need exists for a dosimeter that can accurately measure dose distributions directly and produce 3D dose maps. Some radiation therapy and brachytherapy treatments require mapping the dose distributions in high-resolution (typically < 1 mm). A dosimetry technique that is capable of producing high resolution 3D dose maps of the absorbed dose distribution within tissues is required. Gel dosimetry is inherently a 3D integrating dosimeter that offers high spatial resolution, precision and accuracy. Polymer gel dosimetry is founded on the basis that monomers dissolved in the gel matrix polymerize due to the presence of free radicals produced by the radiolysis of water molecules. The amount of polymerization that occurs within a polymer gel dosimeter can be correlated to the absorbed dose. The gel matrix maintains the spatial integrity of the polymers and hence a dose distribution can be determined by imaging the irradiated polymer gel dosimeter using an imaging modality such as MRI, x-ray computed tomography (CT), ultrasound, optical CT or vibrational spectroscopy. Polymer gel dosimeters, however, suffer from oxygen contamination. Oxygen inhibits the polymerization reaction and hence polymer gel dosimeters must be manufactured, irradiated and scanned in hypoxic environments. Normoxic polymer gel dosimeters incorporate an anti-oxidant into the formulation that binds the oxygen present in the gel and allows the dosimeter to be made under normal atmospheric conditions. The first part of this study was to provide a comprehensive investigation into various formulations of polymer and normoxic polymer gel dosimeters. Several parameters were used to characterize and assess the performance of each formulation of polymer gel dosimeter including: spatial resolution and stability, temporal stability of the R2-dose response, optimal R2-dose response for changes in concentration of constituents and the effects of oxygen infiltration. This work enabled optimal formulations to be determined that would provide greater dose sensitivity. Further work was done to investigate the chemical kinetics that take place within normoxic polymer gel dosimeters from manufacture to post-irradiation. This study explored the functions that each of the constituent chemicals plays in a polymer gel dosimeter. Although normoxic polymer gel dosimeters exhibit very similar characteristics to polyacrylamide polymer gel dosimeters, one important difference between them was found to be a decrease in R2-dose sensitivity over time in the normoxic polymer gel dosimeter compared to an increase in the polyacrylamide polymer gel dosimeters. From an investigation into the function of anti-oxidants in normoxic polymer gel dosimeters, alternatives were proposed. Several alternative anti-oxidants were explored in this study that found that whilst some were reasonably effective, tetrakis (hydroxymethyl) phosphonium chloride (THPC) had the highest reaction rate. THPC was found not only to be an aggressive scavenger of oxygen, but also to increase the dose sensitivity of the gel. Hence, a formulation of normoxic polymer gel dosimeter was proposed, called MAGAT, that comprised: methacrylic acid, gelatin, hydroquinone and THPC. This formulation was examined in a similar fashion to the studies of the other formulations of polymer and normoxic polymer gel dosiemeters. The gel was found to exhibit spatial and temporal stability and an optimal formulation was proposed based on the R2-dose response. Applications such as IVBT require high-resolution dosimetry. Combined with high-resolution MRI, polymer gel dosimetry has potential as a high-resolution 3D integrated dosimeter. Thus, the second component of this study was to commission a micro-imaging MR spectrometer for use with normoxic polymer gel dosimeters and investigate artifacts related to imaging in high-resolutions. Using high-resolution MRI requires high gradient strengths that, combined with the Brownian motion of water molecules, was found to produce an attenuation of the MR signal and hence lead to a variation in the measured R2. The variation in measured R2 was found to be dependent on both the timing and amplitude of pulses in the pulse sequence used during scanning. Software was designed and coded that could accurately determine the amount of variation in measured R2 based on the pulse sequence applied to a phantom. Using this software, it is possible to correct for differences between scans using different imaging parameters or pulse sequences. A normoxic polymer gel dosimeter was irradiated using typical brachytherapy delivery and the resulting dose distributions compared with dose points predicted by the computerized treatment planning system.The R2-dose response was determined and used to convert the R2 maps of the phantoms to dose maps. The phantoms and calibration vials were imaged with an in-plane resolution of 0.1055 mm/pixel and a slice thickness of 2 mm. With such a relatively large slice thickness compared to the in-plane resolution, partial volume effects were significant, especially in the region immediately adjacent the source where high dose gradients typically exist. Estimates of the partial volume effects at various distances within the phantom were determined using a mathematical model based on dose points from the treatment planning system. The normalized and adjusted dose profiles showed very good agreement with the dose points predicted by the treatment planning system.

A radioterapia externa pós-operatória em mulheres diagnosticadas com câncer de mama em estágio inicial é tido como um procedimento padrão, no entanto durante o planejamento para irradiação do volume alvo as possíveis incertezas dosimétricas introduzidas dado o movimento respiratório intrínseco da paciente são desconsideradas. Este estudo avalia não apenas a influência da respiração na distribuição tridimensional da dose, mas como essa distribuição se modifica dado a técnica radioterápica empregada para o tratamento. Três técnicas de planejamento foram analisadas: a radioterapia conformacional tridimensional (3D-RT) com filtros, a radioterapia com intensidade modulada (IMRT) usando planejamento direto e o IMRT inverso. A fim de simular o movimento de contração e expansão da caixa torácica, utilizou-se uma plataforma com amplitudes de oscilação pré-determinadas, sendo a frequência de oscilação provida por uma fonte de tensão variável. Para simular a mama usou-se objetos simuladores semiesféricos preenchidos com gel dosimétrico (MAGIC-f). Os planejamentos para cada técnica foram realizados sobre a mesma tomografia computadorizada (CT) do objeto simulador preenchido com água no modo estático. Foram produzidos três lotes de dosímetro gel para o projeto, cada lote foi irradiado com uma técnica radioterápica diferente, sendo que cada lote inclui cinco objetos simuladores e um conjunto de nove tubos de calibração preenchidos com gel MAGIC-f. O primeiro dos objetos simuladores é utilizado como referência, o segundo é irradiado no modo estático, os demais são irradiados em diferentes amplitudes, respectivamente: 0,34 cm, 0,88 cm e 1,22 cm. A informação volumétrica de dose foi obtida utilizando imagens por ressonância magnética nuclear (IRMN), para cada lote foram adquiridos IRMN com sequência multi spin echo e os mapas de relaxometria, que são associados à dose, foram extraídos em um software desenvolvido e aprimorado pelo nosso grupo de pesquisa. A comparação quantitativa dos mapas de relaxometria dos objetos simuladores em movimento em relação ao modo estático foi realizado pelo índice gamma tridimensional (3% / 3mm / 15% Threshold). Para o 3D-RT a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 96,44%, para amplitude de 0,88 cm foi de 93,23% e para amplitude de 1,22 cm foi de 91,65%. Para o IMRT direto a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 98,42%, para amplitude de 0,88 cm foi de 95,66% e para amplitude de 1,22 cm foi de 94,31%. Para o IMRT inverso a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 94,49%, para amplitude de 0,88 cm foi de 93,51% e para amplitude de 1,22 cm foi de 86,62%. A partir dos resultados, infere-se que a movimentação respiratória de baixa amplitude, para tratamentos de câncer de mama, não é um fator preocupante para a rotina clínica, porém o aumento da amplitude da oscilação aumenta a inomogeneidade de dose e pode afetar os parâmetros dosimétricos da cobertura do volume alvo em relação ao planejamento do tratamento. Observou-se em conjunto que a distribuição de dose se modifica claramente com a técnica em uso e no caso do IMRT inverso para amplitude de oscilação de 1,22 cm a aprovação no índice gamma foi menor que 90% / External postoperative radiotherapy in women diagnosed with early stage breast cancer is considered as a standard procedure, however during planning for target volume irradiation as possible dosimetric uncertainties reabsorption of the patient\'s intrinsic respiratory movement are disregarded. This study evaluates not only the influence of respiration on the three-dimensional distribution of the dose but how this distribution is modified due to the radiotherapy technique used for treatment. Three planning techniques were analyzed: three-dimensional conformational radiotherapy (3D-RT) with filters, intensity-modulated radiotherapy (IMRT) using direct planning and inverse IMRT. In order to simulate the movement of contraction and expansion of the chest wall, a platform with predetermined oscillation amplitudes was used, the oscillation frequency was provided by a variable voltage source. To simulate the breast, semi-spherical simulator objects filled with dosimetric gel (MAGIC-f) were used. The plannnings for each technique were performed on the computerized tomography (CT) of the simulator object filled with water in static mode. Three batches of gel dosimeters were prepared for the project, each batch was irradiated with a different radiothermic technique and comprised five simulator objects and a set of nine calibration tubes filled with MAGIC-f gel. The first simulator objects is used as reference, the second is irradiated in the static mode, the others are irradiated using different amplitudes, respectively: 0,34 cm, 0,88 cm and 1,22 cm. Volumetric dose information was obtained using Nuclear Magnetic Resonance Imaging, each batch was scanned with a multi spin echo sequence and the dose-related relaxometry maps were extracted in a software developed and improved by our Group of research. The quantitative comparison of the relaxometry maps of the moving simulator objects with respect to the static mode was performed by the three-dimensional gamma index (3% / 3mm / 15% threshold). For the 3D-RT, the percentage of approved points of the static object with respect to the oscillator in the amplitude of 0.34 cm was 96.44%, for amplitude of 0.88 cm was 93.23% and for amplitude of 1.22 cm was 91.65%. For the direct IMRT the percentage of approved points of the static object in relation to the oscillator in the amplitude of 0.34 cm was 98.42%, for amplitude of 0.88 cm was 95.66% and for amplitude of 1.22 cm was 94.31%. For the inverse IMRT, the percentage of approved points of the static object in relation to the oscillator in the amplitude of 0.34 cm was 94.49%, for amplitude of 0.88 cm was 93.51% and for amplitude of 1.22 cm was 86.62%. From the results, it is inferred that a low-amplitude respiratory movement, for breast cancer treatments, is not a worrying factor for clinical routine, however, increasing the amplitude of the oscillation increases the inomogeneity of the dose and this affects the dosimetry parameters of the target volume coverage. It was observed that the dose distribution changes with the technique in use and in the case of the inverse IMRT for amplitude of oscillation of 1.22 cm, less than 90% of points were approved in the gamma index evaluation

The overall objective of this study was to develop and characterise new normoxic polymer gel formulations for evaluation of complex 3-D treatment volumes for application in radiotherapy dosimetry. Throughout this thesis, the essential characteristics of normoxic polymer gels have been extensively investigated. Studies were performed on the chemical components of the MAGIC gel and an improved formulation was proposed. Various anti-oxidants were studied and different versions of the MAGIC gel with fewer chemicals were developed and named MAGAS and MAGAT gel dosimeters. The ascorbic acid anti-oxidant was found to have a slow oxygen scavenging rate and therefore a delay period between manufacture and irradiation of the MAGAS gel was necessary before the gel became radiation sensitive. Vacuum pumping on the MAGAS gel solution to remove dissolved oxygen was shown to initially increase the R2-dose response and sensitivity of the dosimeter, reducing the time between manufacture and irradiation. Studies of the MAGAS gel for measurement of depth dose showed that MAGAS gel has potential as a clinical radiotherapy dosimetry tool. The radiological properties of MAGIC, MAGAS and MAGAT gels were investigated. Due to their high gelatine and monomer concentration, differences with water were observed for the cross-section ratios for attenuation, energy absorption and collision stopping power coefficient ratios through the therapeutic energy range. It was determined that when using and developing normoxic polymer gels the most important consideration for radiological water equivalence are the mass and relative electron densities. A preliminary study was performed with the hypoxic PAG gel dosimeter combined with tetrakis (hydroxymethyl) phosphonium chloride anti-oxidant to form a normoxic PAG gel dosimeter named PAGAT gel. It was found PAGAT gel compared favourably with previous studies of the hypoxic PAG gel. An extensive study was subsequently undertaken in which PAGAT gel was investigated for a number of essential characteristics. The PAGAT gel formulation showed potential as a normoxic polymer gel for clinical radiotherapy dosimetry, which has a significantly reduced manufacturing time and procedure compared with the hypoxic PAG gel dosimeter. The radiological attenuation properties of the PAGAT and MAGAT gels were investigated as a feasibility study for using x-ray computerised tomography (CT) as an evaluation technique of normoxic polymer gels. CT was shown to have potential as an evaluation tool for measuring the dose response of normoxic polymer gel dosimeters. An investigation was performed on the CT diagnostic dose response of normoxic polymer gels. Normoxic polymer gels were found to have potential for use as a specialised tool in measuring computerised tomography dose index (CTDI) for acceptance testing and quality assurance of CT scanners in diagnostic radiology. These findings provide a significant contribution toward the development and successful implementation of normoxic polymer gel dosimetry to clinical radiotherapy.

A radioterapia externa pós-operatória em mulheres diagnosticadas com câncer de mama em estágio inicial é tido como um procedimento padrão, no entanto durante o planejamento para irradiação do volume alvo as possíveis incertezas dosimétricas introduzidas dado o movimento respiratório intrínseco da paciente são desconsideradas. Este estudo avalia não apenas a influência da respiração na distribuição tridimensional da dose, mas como essa distribuição se modifica dado a técnica radioterápica empregada para o tratamento. Três técnicas de planejamento foram analisadas: a radioterapia conformacional tridimensional (3D-RT) com filtros, a radioterapia com intensidade modulada (IMRT) usando planejamento direto e o IMRT inverso. A fim de simular o movimento de contração e expansão da caixa torácica, utilizou-se uma plataforma com amplitudes de oscilação pré-determinadas, sendo a frequência de oscilação provida por uma fonte de tensão variável. Para simular a mama usou-se objetos simuladores semiesféricos preenchidos com gel dosimétrico (MAGIC-f). Os planejamentos para cada técnica foram realizados sobre a mesma tomografia computadorizada (CT) do objeto simulador preenchido com água no modo estático. Foram produzidos três lotes de dosímetro gel para o projeto, cada lote foi irradiado com uma técnica radioterápica diferente, sendo que cada lote inclui cinco objetos simuladores e um conjunto de nove tubos de calibração preenchidos com gel MAGIC-f. O primeiro dos objetos simuladores é utilizado como referência, o segundo é irradiado no modo estático, os demais são irradiados em diferentes amplitudes, respectivamente: 0,34 cm, 0,88 cm e 1,22 cm. A informação volumétrica de dose foi obtida utilizando imagens por ressonância magnética nuclear (IRMN), para cada lote foram adquiridos IRMN com sequência multi spin echo e os mapas de relaxometria, que são associados à dose, foram extraídos em um software desenvolvido e aprimorado pelo nosso grupo de pesquisa. A comparação quantitativa dos mapas de relaxometria dos objetos simuladores em movimento em relação ao modo estático foi realizado pelo índice gamma tridimensional (3% / 3mm / 15% Threshold). Para o 3D-RT a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 96,44%, para amplitude de 0,88 cm foi de 93,23% e para amplitude de 1,22 cm foi de 91,65%. Para o IMRT direto a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 98,42%, para amplitude de 0,88 cm foi de 95,66% e para amplitude de 1,22 cm foi de 94,31%. Para o IMRT inverso a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 94,49%, para amplitude de 0,88 cm foi de 93,51% e para amplitude de 1,22 cm foi de 86,62%. A partir dos resultados, infere-se que a movimentação respiratória de baixa amplitude, para tratamentos de câncer de mama, não é um fator preocupante para a rotina clínica, porém o aumento da amplitude da oscilação aumenta a inomogeneidade de dose e pode afetar os parâmetros dosimétricos da cobertura do volume alvo em relação ao planejamento do tratamento. Observou-se em conjunto que a distribuição de dose se modifica claramente com a técnica em uso e no caso do IMRT inverso para amplitude de oscilação de 1,22 cm a aprovação no índice gamma foi menor que 90% / External postoperative radiotherapy in women diagnosed with early stage breast cancer is considered as a standard procedure, however during planning for target volume irradiation as possible dosimetric uncertainties reabsorption of the patient\'s intrinsic respiratory movement are disregarded. This study evaluates not only the influence of respiration on the three-dimensional distribution of the dose but how this distribution is modified due to the radiotherapy technique used for treatment. Three planning techniques were analyzed: three-dimensional conformational radiotherapy (3D-RT) with filters, intensity-modulated radiotherapy (IMRT) using direct planning and inverse IMRT. In order to simulate the movement of contraction and expansion of the chest wall, a platform with predetermined oscillation amplitudes was used, the oscillation frequency was provided by a variable voltage source. To simulate the breast, semi-spherical simulator objects filled with dosimetric gel (MAGIC-f) were used. The plannnings for each technique were performed on the computerized tomography (CT) of the simulator object filled with water in static mode. Three batches of gel dosimeters were prepared for the project, each batch was irradiated with a different radiothermic technique and comprised five simulator objects and a set of nine calibration tubes filled with MAGIC-f gel. The first simulator objects is used as reference, the second is irradiated in the static mode, the others are irradiated using different amplitudes, respectively: 0,34 cm, 0,88 cm and 1,22 cm. Volumetric dose information was obtained using Nuclear Magnetic Resonance Imaging, each batch was scanned with a multi spin echo sequence and the dose-related relaxometry maps were extracted in a software developed and improved by our Group of research. The quantitative comparison of the relaxometry maps of the moving simulator objects with respect to the static mode was performed by the three-dimensional gamma index (3% / 3mm / 15% threshold). For the 3D-RT, the percentage of approved points of the static object with respect to the oscillator in the amplitude of 0.34 cm was 96.44%, for amplitude of 0.88 cm was 93.23% and for amplitude of 1.22 cm was 91.65%. For the direct IMRT the percentage of approved points of the static object in relation to the oscillator in the amplitude of 0.34 cm was 98.42%, for amplitude of 0.88 cm was 95.66% and for amplitude of 1.22 cm was 94.31%. For the inverse IMRT, the percentage of approved points of the static object in relation to the oscillator in the amplitude of 0.34 cm was 94.49%, for amplitude of 0.88 cm was 93.51% and for amplitude of 1.22 cm was 86.62%. From the results, it is inferred that a low-amplitude respiratory movement, for breast cancer treatments, is not a worrying factor for clinical routine, however, increasing the amplitude of the oscillation increases the inomogeneity of the dose and this affects the dosimetry parameters of the target volume coverage. It was observed that the dose distribution changes with the technique in use and in the case of the inverse IMRT for amplitude of oscillation of 1.22 cm, less than 90% of points were approved in the gamma index evaluation

No description available.