Made available in DSpace on 2014-10-09T12:41:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:04Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-03-30Bitstream added on 2014-06-13T20:40:11Z : No. of bitstreams: 1 fernandes_dm_me_bauru.pdf: 957024 bytes, checksum: 166e807e8c28852f41e7733849398194 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho teve como objetivo estudar as características dosimétricas do polímero poly-[1,1-bis(ethynyl)-4,4-bipheny(bis-tributylphosphine)Pt(11)] (Pt-DEBP) frente à radiação gama. Para realização dos experimentos dissolveu-se o polímero Pt-DEBP, contendo dez unidades monoméricas, em solventes orgânicos - clorofórmio e totueno. As amostras foram irradiadas em quatro concentrações (0,0500; 0,0375; 0,0250; 0,0113 mg/mL) e em duplicatas, com doses que variaram de 1 a 90 Gy. Os resultados foram avaliados com base em técnicas espectroscópias, como a espectroscopia de absorção óptica (UV-VIs), fluorescência (emissão), fluorescência com resolução temporal (FRT) e infravermelho com transformada de Fourier (FTIR). Para soluções de Pt-DEBP em clorofórmio, nota-se uma alteração na posição da banca principal (л-л *) de absorção óptica para menores comprimentos de onda (blue-shift), aliado a uma diminuição da intensidade de absorção, á medida em que se aumenta a dose de radiação. Na espectroscopia de fluorescência, observou-se um deslocamento para maiores comprimentos de onda (red-shift) aliado a um aumento de intensidade na banda de emissão com aumento da dose de radiação. Experimentos de FRT, das amostras irradiadas em clorofórmio indicam a presença de um novo centro emissor. Os espectros de infravermelho com transformada de Fourier (FTIR) comprovam a entrada de cloro na cadeia polimérica, justificando o blue-shift obervado nos espectros de absorção e o novo centro emissor responsável pela alteração nos espectros de emissão. Além disso, foi analisado o comportamento linear dos resultados obtidos nos estudos de absorção e fluorescência, tomando como base a relação entre comprimento de onda máxima de absorção com a dose e, para o segundo caso, a relação entre... / This work aimed to study the dosimetric characteristics of the polymer of the polymerpoly-[1,1-bis (ethynyl) -4,4 biphenyl (bis-tributylphosphine) Pt (II)] (Pt-DEBP) compared to radiation gamma. The Pt-DEBP polymer, containing ten monomer units, was then dissolved in organic solvents as chloroform and toluene. The samples were irradiated at four concentrations (0.0500, 0.250, 0.0113 mg / mL) in duplicate, with radiation doses ranging from 1 to 90 Gy. The results were evaluated based on spectroscopic techniques such as optical absorption spectroscopy (UV-Vis), fluorescence (emission), time resolved fluorescence (FRT) and Fourier transform infrared (FTIR). For DEBP-Pt solutions in chloroform, there is a shift in the position of the main optical absorption band (л-л *) to lower wavelength (blue-shift), allied to a decreasing absorption intensify with increasing radiation dose. In fluorescence spectroscopy, there was a shift to longer wavelengths (red-shift) allied to an increasing emission intensify with increasing radition dose. FRT experiments on irradiated samples dissolved in chloroform indicated the presence of a new emitter center. FTRI spectra show the incorporation of chlorine in polymer chain, justifying the blue-shift observed in the absorption spectra and the new emission center. In addition, the behavior of linear results in the aborption and fluorescence studies was investigated based on the relationship between the wavelength of maximum absorption/emission and the radiation dose. For both cases, a linear behavior was observed in relation to the sample concentration. Repeatability and stability tests were also performed. For the samples dissolved in tolluene, there was no significant shift of the spectrum of absorption or fluorescence for all doses. The results show that the Pt-DEBP polymer dissolved in chloroform can be used as a dosimer for y-ray doses between... (Complete abstract click electronic access below)

Nas décadas de 1960 e 1970, as primeiras investigações de dosímetros termoluminescentes (TLD), especificamente, os picos dosimétricos, rapidamente revelaram um número surpreendente de fenômenos que poderiam estar diretamente relacionados à densidade de ionização. Um pouco mais tarde, nos anos 80 e no início dos anos 90, a radiação aparentemente desconectada induziu fenômenos que foram descobertos em outros sistemas baseados em fluoreto de lítio (LiF). A última década, no entanto, testemunhou o surgimento de vários modelos, encabeçado através de uma compreensão mais profunda dos mecanismos TL subjacentes, bem como na modelagem micro dosimétrica e especificamente desenvolvida para explicar fenômenos de densidade de ionização. Muitas aplicações em radioterapia fornecem níveis de dose de radiação superiores a 1 Gy, porém em radiodiagnóstico estão na faixa de alguns mGy, e níveis muito altos de precisão são necessárias para promover o tratamento ideal. Isto exige uma atenção muito cuidadosa aos protocolos de medição altamente detalhados, bem como à calibração demorada de todos os TLDs para corrigir a não-linearidade da resposta à dose. Essas propriedades podem variar de lote para lote e também podem ser uma função da exposição à radiação, do aquecimento e histórico de manuseio. Deste modo, mesmo com excelentes avanços nos estudos do TLD com relação aos tratamentos térmicos e às formas de análise da curva de emissão TL, é necessário continuar os estudos a fim de possibilitar uma melhor utilização desta técnica na clínica. Uma análise computadorizada da curva de emissão (CGCA do inglês, computadorized glow curve analisys) foi implementada utilizando dados provenientes do software WinREMS de dosímetros TL que absorvem e armazenam a energia da radiação ionizante, reemitida na forma de fóton na região do ultravioleta visível. A luz emitida é, então, detectada por uma fotomultiplicadora e correlacionada à dose absorvida recebida pelo material. Os picos de emissão foram ajustados por meio de um algoritmo no programa MATLAB adotando-se o modelo de cinética de primeira ordem. O material testado foi o LiF:Mg,Ti (fluoreto de lítio dopado com magnésio e titânio) da marca Harshaw e a qualidade do ajuste foi determinada por um parâmetro chamado figura de mérito (FOM - do inglês, figure of merit). O menor FOM obtido para o grupo de dosímetros foi de 1,04 % e o maior foi de 9,79 %. Também foi avaliada a dose mínima detectável, utilizando o parâmetro que apresentou melhor desempenho, segundo a homogeneidade do grupo de dosímetros. O valor médio de dose mínima apresentado foi 28 µGy. Os resultados de reprodutibilidade, índice de variabilidade do detector (DVI - do inglês, device variability index) foi 14,01 %, que pode ser explicado pelo alto número de dosímetros no lote. Então, com a diminuição do tempo de preparo do dosímetro e com a análise computadorizada da curva de emissão, a utilização clínica do TLD torna-se mais viável, visto que não houve interferência na sensibilidade do dosímetro. Apesar de a reprodutibilidade ter sido a cima do esperado, é indicado uma correção individual para cada dosímetro e o descarte daqueles que apresentarem valores mais discrepantes comparado ao lote. / In the decades of 1960 and 1970, the first investigations of termoluminescentes dosimeters (TLD), specifically, the dosimetric peaks quickly revealed a surprising number of phenomena that could be directly related to the density of ionization. A little later, in the years 80 and 90 at the beginning of the year, seemingly disconnected radiation induced phenomena were discovered on other systems based on lithium fluoride (LiF). The last decade, however, has witnessed the emergence of several models, spearheaded through a deeper understanding of the underlying TL mechanisms as well as in modeling specifically developed for microdosimetric and explain phenomena of ionization density. Many applications in radiation oncology provide levels of radiation dose in excess of 1 Gy, however in diagnostic radiology are in the range of a few mGy, and very high levels of precision are necessary to promote the ideal treatment. This requires careful attention to the highly detailed measurement protocols, as well as the time-consuming calibration of all TLDs to correct the non-linearity of dose-response. These properties can vary from batch to batch, and can also be a function of exposure to radiation, heating and handling history. In this way, even with excellent advances in the studies of the TLD for the heat treatment and the ways of issuing TL curve analysis, it is necessary to continue studies in order to enable a better use of this technique in the clinic. A computerized analysis of the emission curve (CGCA computadorized glow curve analysis) was implemented using data from the WinREMS software of TL dosimeters that absorb and store energy from ionizing radiation, reissued in the form of photon in the visible ultraviolet. The light emitted is then detected by a photomultiplier and correlated to the absorbed dose received by the material. The emission peaks were adjusted by means of an algorithm in MATLAB program by adopting the model of first-order kinetics. The material tested was the LiF: Mg, Ti (lithium fluoride doped with magnesium and titanium) brand Harshaw and the quality of the fit was determined by a parameter called figure of merit (FOM- figure of merit). The smallest FOM obtained for the group of dosimeters was 1.04% and the highest was 9.79%. Also minimum detectable dose was evaluated, using the parameter that showed better performance, according to the homogeneity of the Group of dosimeters. The average value of minimum dose presented was 28 µGy. The results of reproducibility, index of variability of the detector (DVI-English, device variability index) was 14.01%, which can be explained by the high number of dosimeters in the batch. Then, with the decrease in the time of preparation of the dosimeter and the computerized analysis of the emission curve, the clinical use of the TLD becomes more viable, since there was no interference on sensitivity of the dosimeter. Although the reproducibility have been above expectations, indicated a single correction for each badge and the disposal of those who submit more discrepant values compared to the batch.

Made available in DSpace on 2014-10-09T12:41:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:04Z (GMT). No. of bitstreams: 0 / A mamografia é um método de diagnóstico por imagem que utiliza radiação X. No controle de qualidade dos mamógrafos, as câmaras de ionização são usadas para verificar se os parâmetros de exposição das pacientes estão corretos. Contudo, as câmaras de ionização comerciais para dosimetria em mamografia representam alto custo para clínicas de pequeno e médio porte que desejam ter esse equipamento ou para profissionais que trabalham com controle de qualidade. Assim, a característica inovadora deste trabalho foi desenvolver câmaras de ionização para este fim. Neste trabalho foram projetadas, construídas e caracterizadas câmaras de ionização para feixes de radiação X, no intervalo de energia de mamografia. As câmaras de ionização foram caracterizadas em feixes padronizados de radiação X no LCI/IPEN. Os testes principais de caracterização das câmaras de ionização foram: curva de saturação, linearidade da resposta, dependência energética e angular. Os testes de estabilidade da resposta das câmaras de ionização também foram realizados, apresentando resposta dentro de 2,0 % para estabilidade em longo prazo. Os resultados dos demais testes foram em conformidade com normas internacionais. Essas câmaras de ionização foram ainda submetidas a testes de controle de qualidade de mamógrafos quanto à linearidade das taxas de kerma no ar, à determinação das camadas semirredutoras e das doses glandulares médias. Para a linearidade da taxa de kerma, os valores obtidos foram abaixo dos 10 %, como estabelecido em norma. A dose glandular determinada com as câmaras desenvolvidas apresentaram valores comparáveis com os da câmara de referência testada, com variação prevista em recomendações internacionais. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

New radiation therapy (RT) techniques for treating cancer are continually under development. Our ability to demonstrate the safe and accurate implementation of new RT treatment techniques is dependent on the information provided by current dosimetric tools. Advanced dosimetric tools will become increasingly necessary as treatments become more complex. This work examines the readout of an advanced dosimeter --- the polyacrylamide, gelatin, and tetrakis (hydroxymethyl) phosphonium chloride (PAGAT) dosimeter --- using a prototype fan-beam optical computed tomography (CT) scanner. A number of developments sought to improve the performance of the optical CT device. A new fan-creation method (laser diode module) and new matching tank were introduced. Artefact removal techniques were developed to remove flask seam artefacts and ring artefacts via sinogram space. A flask registration technique was established to achieve reproducible placement of flasks in the optical CT scanner. A timing-correction technique was implemented to allow for the scanning of continuously rotating samples. A number of experiments examined factors related to the PAGAT dosimeter. Comparisons of post-irradiation scans to pre-irradiation scans improved dosimeter readout quality. Changes to the PAGAT dosimeter cooling/scanning routine provided further improvements to dosimeter readout. Evaluations of calibration curves showed that a linear calibration curve was less capable of describing PAGAT dose response than a quadratic calibration curve. Intra-gel calibration using another dose distribution was shown to be no less accurate than self calibration, but inter-gel calibrations saw a statistically significant increase in absolute readout errors. A set of investigations examined how optical CT scanning protocols affected readout quality for PAGAT dosimeters. Doubling the dose delivered to the dosimeter doubled the signal-to-noise ratio. Acquiring and averaging additional light profiles at each projection angle provided only slight reductions in readout noise. Sampling a higher number of projection angles provided substantial reductions in readout noise. Those reductions in readout noise were not lost when sinograms with many projections were encapsulated into sinograms of fewer projection angles. Detector element binning (sinogram space) and pixel binning (image space) also provided substantial reductions in readout noise. None of these elements of the scanning protocol had statistically significant effects on readout errors. Finally, distinct imaging artefacts seen throughout this work were shown to be caused by radiation-induced refractive index changes in PAGAT dosimeters. Radiation-induced refraction (RIR) artefacts result when dose gradients caused the refraction of fan-beam raylines towards high dose regions. A filtering technique was developed to remove RIR artefacts in sinogram space, but this technique caused substantial blurring to the measured dose distribution. / Graduate / 0760 / 0756 / 0752 / warreng1983@gmail.com

Thesis (MSc (Radiography))--Cape Peninsula University of Technology, 2019 / Introduction: Intracranial aneurysm coil embolization is a fluoroscopically guided interventional procedure that is often preferred over surgical clipping for the treatment of intracranial aneurysms. Fluoroscopically guided procedures are associated with high levels of radiation doses which have the potential to induce skin injuries; and this necessitates adherence to radiation protection measures, especially the optimization of radiation exposure during fluoroscopically guided procedures. Optimization of radiation exposure can be achieved by applying the as low as reasonably achievable (ALARA) principle and by implementing diagnostic reference levels (DRLs). Monitoring and documentation of radiation doses at the end of each procedure is also essential to identify patients that are at risk of developing radiation-induced injuries for possible follow-up. Aim: This research study aimed to determine the average radiation dose to patients' thyroid glands and skin during intracranial aneurysm coil embolization. The objectives were to establish preliminary DRLs for intracranial aneurysm coil embolization; to ascertain whether the anatomical location of the intracranial aneurysm had an effect on the radiation dose and to compare the measured thyroid gland and skin doses to the Monte Carlo calculated doses. Methods: A prospective quantitative research study was conducted on 34 participants who had intracranial aneurysms that required coil embolization during the study period. Radiation doses to the anterior neck of participants, over the thyroid gland region, were measured using lithium fluoride thermoluminescent dosimeters (TLDs). In addition, the air-kerma area product (KAP) values were used to determine the participants' skin dose and the DRLs. Considering that it is not possible to perform direct thyroid measurements on human beings, phantom-based simulation studies were performed to evaluate the difference between the dose measured on the anterior neck and the dose measured directly on the thyroid gland. Three different aneurysm coil embolization scenarios were simulated during the phantom-based simulation studies. TLDs were placed on the anterior neck and in the thyroid hole of the phantom, which represents the anatomical location of the thyroid gland, during each simulation. The thyroid and skin doses were also calculated using a Monte Carlo program. The measured thyroid gland and skin doses were compared to the doses obtained from Monte Carlo calculations. Results: The average percentage difference between the anterior neck doses and thyroid radiation doses was found to be 61%. This value was added to the radiation dose measured on the anterior neck of participants to obtain the thyroid absorbed doses during coil embolization procedures. The thyroid absorbed doses ranged between 3.2 and 20.95 mGy with a mean of 11.25 mGy. The KAP values ranged between 33 and 125 Gy.cm2. The DRL established during this study was 68 Gy.cm2, 616 image frames and 30 minutes of fluoroscopy time. There was no agreement between measured thyroid dose and calculated thyroid doses while there was strong positive correlation between measured and calculated skin doses. The results showed no statistically significant relationship between aneurysm location and the radiation dose. Conclusion: The skin doses in this research study were below the threshold doses suggested in the literature for deterministic effects of radiation. The study results therefore suggest that patients that undergo intracranial aneurysm coil embolization at the research site are not at risk of developing radiation-induced skin injuries. The established DRLs were also lower than internationally published DRLs for intracranial aneurysm coil embolization.

No description available.

<p>  </p> <p>The research and development for this dissertation focused on the VOC-free, biodegradable “green” polylactic acid (PLA) polymer for deriving tailored properties via thermal and ionizing radiation and targeted for the following three areas: (i) Deriving a first-of-kind wear-resistant distortion-free coating for luxury vinyl flooring tiles (to replace PVC), (ii) Deriving an ultra-low cost, rapid turnaround, and versatile gamma-neutron solid state detector-dosimeter (PLAD), and, (iii) for studying the possible use general purpose adhesion of various substrates at elevated temperatures. Collectively, the PLA based technology is referred to as PLATech. </p> <p>Polylactic acid (PLA) bio-renewable green polymer films were studied for their use as alternate to polyvinyl chloride (PVC) for deployment as the wear layer (WL) for luxury vinyl tiles. The WL is to be adhesively bonded to a composite layer comprising a thin ~0.08mm print layer (PL) bonded onto a relatively thick ~2.5mm ethyl vinyl acetate (EVA) backing layer (BL). Challenges included studying for: optimizing for the combinations of PLA polymer film types and thicknesses that are wear resistant enough, joined under hot press temperature, compression loading and time duration of compression for attaining key metric of adhesion related peel strength of over 354 N/mm (7 pli), with minimal (< 2% thickness) distortion of the PL-cum-BL for producing spatially uniform strength sizes ranging from 4”x4” towards 12”x12” LVT; additional challenges involved ensuring adequate WL abrasion resistance commensurate with residential and industrial uses, along with tensile strength and shrinkage similar to that for PVC. Abrasion resistance for the PLA WL varied with film thickness ranging from 450 cycles to over 4,500 cycles for film thicknesses of 0.075 mm and ~0.5mm, respectively. PLA WL tensile strength at failure was found to be 7x higher than that for PVC films of equal thickness (0.5 mm); however, the tensile elongation for PLA film at failure is ~12% versus ~200% for PVC film. High temperature-pressure (93-110℃; 1-3 MPa) combinations with press times ranging from 5 to 20 min. resulted in peel strengths ranging from 177 N/m (~3.5 pli) towards 810 N/m (16 pli). However, these parametric combinations resulted in significant PL disfigurement, BL melting and distortion with over 0.4mm thickness reductions. Peel strength variations were highly non-linear versus compression time, platen temperature/pressure and film thickness. Distortion-free, high peel strength 455-610 N/m(9-12 pli) adhesion and industrial grade WL abrasion resistance (>4,000 cycles) LVTs were successfully produced using 500 mm thick crystalline PLA film compressed onto PL-BL composite layers, with platens heated between 90.5-93℃, under 1 MPa loading, applied for ~5 min. duration. This combination of parameters also allowed scaling of sizes of the composite tiles from 0.1mx0.1m (4”x4”) to ~0.3mx0.3m (12”x12”). The onset of unacceptable distortion and thickness reduction occurs at/beyond ~ 95℃ and is attributed mainly to plastic deformation for the EVA-based base layer, and affirmed via DSC test results. Effects of PLA WL surface pre-treatment were studied for impact on peel strength of PLA-LVTs. Silicone layer coating nominally used by suppliers (and used for the bulk of the studies reported herein) did not lead to noticeable changes in bond strength when using a single PLA WL, but, surprisingly close to 100% increase was noted for PLA-LVTs produced using a double lap layer of non-silicone coated PLA films. Corona plasma discharge treated PLA WL surprisingly resulted in a significant (~90%) degradation of peel strength. Finally, sand paper roughened PLA WL showed no significant effect on resulting peel strength.</p> <p>PLAD related studies were motivated from observations that PLA resin responds well in terms of mechanical, thermal and rheological property variations when subject to ionizing radiation in the 1–100 kGy (100-10,000 kRad) range–of significant interest in biomedical and general nuclear industry applications. Co-60 was used as the mainstay source for gamma irradiation. It was found that PLA resin responds well in terms of rheology and porosity metrics with an absorbed gamma dose (Dg). In this work, rheological changes were ascertained via measuring the differential mass loss ratio (MLR) of irradiated PLA placed within PTFE-framed (40 mm × 20 mm × 0.77 mm) cavities bearing ~0.9 g of PLA resin and pressed for 12–16 min in a controlled force hot press under ~6.6 kN loading and platens heated to 227 °C for the low Dg range: 0–11 kGy (0-1,100 kRad); and to 193 °C for the extended Dg range: 11–120 kGy (1,100-12,000 kRad). MLR varied quadratically from 0.05 to ~0.2 (1σ ~0.007) in the 0–11 kGy (0-1,100 kRad) experiments, and from 0.05 to ~0.5 (1σ ~0.01) in the 0–120 kGy (0-12,000 kRad) experiments. Rheological changes from gamma irradiation were modeled and simultaneously correlated with void-pocket formations, which increase with Dg. A single PLA resin bead (~0.04 g) was compressed 5 min at 216 °C in 0–16 kGy (0-1,600 kRad) experiments, and compressed 2 min at 232 °C in the 16–114 kGy (1,600-14,000 kRad) experiments, to form sturdy ~100 µm thick wafers in the same press. Aggregate coupon porosity was then readily measurable with conventional optical microscope imaging and analyzed with standard image processing; this provided complementary data to MLR. Average porosity vs. dose varied quadratically from ~0 to ~15% in the 0–16 kGy (0-1,600 kRad) range and from ~0 to ~18% over the 16–114 kGy (1,600-14,000 kRad) range. These results provide evidence for utilizing “green”/renewable (under $0.01) PLA resin beads for rapid and accurate (+/-5–10%) gamma dosimetry over a wide 0–120 kGy (0-12,000 kRad) range, using simple to deploy mass and void measuring techniques using common laboratory equipment. In addition to Co-60 gamma irradiations alone, irradiation studies were also initiated using the Purdue University Reactor (PUR-1) irradiation capabilities in order to further develop and characterize PLAD technology. It was found that the afore-mentioned MLR and porosity metrics did not offer the ability to monitor for neutron dose; this was overcome in scoping studies with an alternate metric, Ratio of Mass Dissolved (RMD) of irradiated PLA in acetone at elevated temperatures. It was found that below ~54℃, PLA dissolution correlated very well with gamma irradiation dose. At and above ~54℃ the combined effect of neutron and gamma irradiation dose appears feasible to determine. </p> <p>The effect of gamma radiation induced crosslinking the adhesion bonding strength at room temperature and elevated temperatures were studied. For room temperature applications, IngeoTM 4043D semi-crystalline PLA was first used to bond steel dowels. Bonding strength enhancement of ~28% was obtained with the addition of 10wt% Triallyl Isocyanurate (TAIC) and cross-linked under 20 kGy (2,000 kRad) gamma irradiation dose. For elevated temperature assessments, IngeoTM 10361D amorphous PLA was then used to bond aluminum lap-joint shear samples as a control. For studying for application for elevated temperatures, tests were conducted with addition of 3wt% TAIC and 50 kGy (5,000 kRad) gamma dose. Under shear loading, an enhancement of ~30% working temperature improvement was attainable raising the temperature at failure from ~70℃ towards ~100℃. Alternative crosslinking agent Dicumyl peroxide (DCP) was also explored and indicated little to no benefits. </p>

Radiotherapy is a prominent cancer treatment modality in medicine, aiming to deliver adequate doses to the target while minimizing harm to healthy tissue. Recent advancements in computer technology, machine engineering, and imaging have facilitated intricate treatment planning and accurate radiation administration. These advancements have allowed for more precise dose distributions to be delivered to cancer patients. However, even small discrepancies in setup or delivery can result in significant dose variations. While treatment planning systems provide 3D dose calculations, there is currently a lack of 3D measurement tools in the clinic to verify the accuracy of dose calculation and delivery. Presently, medical physicists rely on 2D dose plane comparisons with treatment planning calculations using gamma index analyses. However, these results do not directly correlate with clinical dose-volume constraints, and detecting delivery errors using 1D or 2D dosimetry is challenging. The implementation of 3D dosimetry not only ensures the safety of radiation treatment but also facilitates the development of new emerging radiation treatment techniques. This study aims to commission and validate a clinically viable optical scanner for 3D dosimetry and apply the developed system to address current clinical and pre-clinical challenges, thereby advancing our understanding of treatment uncertainties in modern radiotherapy. The optical CT scanner that was developed comprises four key components: an LED illuminator, an aquarium with matching fluid, a fiber optic taper, and a CCD camera. The LED illuminator emits uniform and parallel red light at a peak wavelength of 625 nm and a full width at half maximum (FWHM) of 20 nm in continuous mode. The aquarium is constructed with transparent acrylic walls and is designed to accommodate the 3D dosimeter PRESAGE, which can be fixed on a rotation stage inside the tank. Clear acrylic has excellent optical clarity and light transmission, with a refractive index of 1.49 that is close to the average refractive index (1.54) of PRESAGE. To match the refractive index of the 3D dosimeters, a matching liquid composed of 90% Octyl Salicylate and 10% Octyl-P-Methoxy Cinnamate is filled in the tank. The fiber optic taper serves two functions: first, it demagnifies the projection images while preserving their shape, and second, it effectively reduces the acceptance angle of the light reaching the CCD camera. The CCD camera used in the system is an Allied Vision model with a resolution of 0.016 mm, capable of acquiring 2D projection images from various angles. The principle of the optical CT scanner follows that of CT imaging, where 2D projection images from different angles are used to reconstruct volumetric 3D dose images using the filtered back projection technique. To validate the dosimetric measurements and assess the uncertainties of the 3D dosimetry system, 21 benchmark experiments, including mechanical, imaging, and dosimetry tests were conducted. Furthermore, the developed system was employed for various applications, including patient-specific IMRT QA, small field dosimetry using kilovoltage and megavoltage beams, as well as end-to-end testing of stereotactic radiosurgery. A comprehensive analysis assessed uncertainties in each scanner component. Mechanical tests showed maximum uncertainties below 1%. By employing background subtraction and calibration techniques, measurement uncertainty was reduced to <1% in the optimal dose range. Background subtraction resulted in a remarkable 77% reduction in uncertainty by mitigating artifacts, ambient light, and refractive light. Reproducibility was excellent, with mean and standard deviation of dose differences below 0.4% and 1.1%, respectively, in three repeat scans. Dose distribution measurements exhibited strong agreement (passing rates: 98%-100%) between 3D measurements, treatment planning calculations, and EBT3 film dosimetry. Results confirm the optical CT scanner's robustness and accuracy for clinical 3D radiation dosimetry. The study also demonstrates that the developed 3D dosimetry system surpasses the limitations of traditional 2D gamma tests by providing clinicians with more clinically relevant information. This includes measured dose-volume histograms (DVHs) and the evaluation of gamma failing points in 3D space, enabling a comprehensive assessment of individual treatment plans. Furthermore, the study showcased the feasibility of utilizing this system to characterize a radiosurgery platform. It successfully assessed mechanical and dosimetric errors in off-axis delivery and evaluated the accuracy of treatment planning dose calculations, including modeling small fields, out-of-field dose, and multi-leaf collimator (MLC) characteristics. In addition, compelling evidence was presented that the high-resolution 3D dosimeter used in this study is capable of accurate dosimetry for both megavoltage and kilovoltage small fields. Importantly, the dosimeter exhibits no energy or dose rate dependence, further supporting its reliability and suitability for precise dosimetry measurements. The intricate and three-dimensional nature of dose distributions in modern radiotherapy necessitated the development of 3D dosimetry measurements, particularly for treatments with precise margins, such as SRS and SBRT. The newly developed 3D dosimetry system offers significant enhancements to current QA practices, delivering more clinically relevant comparison results and bolstering patient safety. Furthermore, it can be utilized for independent inspections across multiple institutions or remote dosimetry verification. Beyond its applications in clinical settings, the presented 3D dosimetry system holds the potential to expedite the development and utilization of novel radiation platforms.

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)