A braquiterapia de alta taxa de dose é uma das modalidades mais utilizadas em braquiterapia para o tratamento de câncer. Os diversos avanços tecnológicos, bem como a evolução das técnicas de tratamento tornaram a braquiterapia de alta taxa de dose uma das modalidades de estado da arte para o tratamento de alguns cânceres. Parte deste avanço é creditada à melhoria na acurácia e na prescrição de dose absorvida recomendada ao paciente, ao longo dos anos. Este avanço permite que atualmente seja possível realizar os cálculos dosimétricos, por meio de sistemas de planejamento computadorizado, considerando as heterogeneidades dos pacientes, tais como: tecidos e órgãos com composições diferentes da água (meio de referência em radioterapia), contorno do paciente individualizado, introdução de aplicadores, dentre outros. Tais avanços demandam o controle de qualidade destas ferramentas, com objetivo de assegurar que todo o processo de tratamento seja satisfatório e acurado. Até o momento, a comunidade carece de um sistema experimental capaz de avaliar, considerando os níveis de incerteza, se os sistemas de planejamento computadorizados são aptos a considerar a heterogeneidade dos tratamentos. Neste trabalho, apresentamos o desenvolvimento de medidas experimentais em um objeto simulador, com capacidade de mensurar as diferenças introduzidas pela heterogeneidade por meio de três técnicas dosimétricas experimentais: termoluminescência, filmes radiocrômicos e ionométrica. Os resultados experimentais foram comparados com as simulações de Monte Carlo e com um sistema de planejamento computadorizado comercial, apto a realizar correções de heterogeneidade em braquiterapia. Discutimos as principais etapas de desenvolvimento deste objeto simulador, seus resultados experimentais e as comparações com os demais sistemas. As conclusões e as etapas futuras deste projeto também são apresentadas. / High dose rate brachytherapy is one of the most widely used modalities in brachytherapy for cancer treatment The various technological advances and the development of treatment techniques have made high dose rate brachytherapy as one of the state of the art methods for the treatment of some cancers. Part of this progress is credited to the improvement in the accuracy and absorbed dose prescription recommended to patients over the years. This advance currently allows the possibility of performing dosimetric calculations, by means of computerized planning systems, considering the heterogeneity of patients, such as: tissues and organs with different water compositions (reference medium in radiotherapy), individualized patient\'s contour and introduction of applicators, among others. Such advances require quality control of these tools, in order to ensure that the entire treatment process is satisfactory and accurate. Nowadays, the community needs an experimental system capable of evaluating, since the uncertainty levels if the computerized planning systems are able to consider the heterogeneity of treatments. In this project, we present the development of experimental measurements into a phantom, capable of measuring the differences introduced by heterogeneity through three experimental dosimetric techniques: thermoluminescence, radiochromic films and ionometric. The experimental results were compared with the Monte Carlo simulations and a commercial treatment planning system able to perform correction of heterogeneity in brachytherapy. We discuss the main stages of development of this phantom, their experimental results and comparisons with other systems. The conclusions and future steps to complete this project are also presented.

In this thesis, we aim to develop fundamentally new techniques and algorithms for efficiently computing rotating-shield brachytherapy (RSBT) treatment plans. We propose that these algorithms will pave the way for making RSBT available in clinical practices. RSBT is an intensity modulated high-dose-rate brachytherapy (HDR-BT) technique. Theoretically, RSBT offers advantages over the conventional HDR-BT. Although this technique is promising in theory, its application in practice is still at an early stage. The RSBT technique entails rotating a radiation-attenuating shield about a brachytherapy source to directionally modulate the radiation in an optimized fashion. The unshielded brachytherapy source used in conventional HDR-BT delivers radially symmetric dose distributions, thus the intensity modulation capability of the conventional HDR-BT is limited. With the capability of making anisotropic radiation, RSBT will revolutionize the brachytherapy technique through superior dose conformity, increased flexibility and inherent accuracy. Due to the enhanced power of intensity-modulation, RSBT will also enable dose escalation without increasing toxicity to the organs-at-risk, thus improving quality of life for millions of cancer patients. Although the first conceptual RSBT method was proposed more than ten years ago, there are still tremendous challenges for applying it in clinical practices. Creating efficient and automated treatment planning system is one of the major technical obstacles for making RSBT deliverable in the clinic. The time-critical nature of the application significantly increases the difficulty of RSBT treatment planning, demanding innovative techniques for information integration. Therefore, we propose that fundamentally novel technology and algorithms for RSBT treatment planning can make RSBT clinically accessible. The fundamental concept used for this thesis is to decompose the dose optimization step for RSBT treatment planning into two steps, namely anchor plan optimization and optimal sequencing. The degree of freedom in anchor plan optimization is controlled at a low level compared to single-step dose optimization, and the optimal sequencing algorithms can efficiently calculate treatment plans by reusing the solutions from anchor plan optimization. Thus, by decomposing the dose optimization, the computational complexity in the two-step method is greatly reduced compared to the single-step method. In the anchor plan optimization, an abstract RSBT delivery model is assumed. The abstract RSBT delivery model assumes that only beams with fixed small azimuthal emission angle, which are called beamlets, will be used during the delivery. An anchor plan is created based on this assumption that only these beamlets will be used. Generally, an anchor plan will be of high quality in the sense of dose distribution, but of low quality in the sense that it has prohibitory long delivery time. In the optimal sequencing step, beamlets will be superposed into beams to reduce the delivery time. By limiting the delivery time to a clinically acceptable level, the anchor plans turn into deliverable plans. Unlike anchor plan optimization, where an abstract RSBT delivery model is assumed, the optimal sequencing step depends on more concrete RSBT delivery models. Specifically, we will study three methods of RSBT, namely the single rotating-shield brachytherapy (S-RSBT), the dynamic rotating-shield brachytherapy (D-RSBT) and the paddle rotating-shield brachytherapy (P-RSBT). We proposed a novel anchor plan dose optimization method as well as novel optimal sequencing methods for each of the RSBT delivery methods studied in this work. We have implemented all the proposed algorithms and experimented with them using real medical data. With the methods proposed in this thesis, the optimization time for creating delivery plans can be controlled within 15 minutes based on the data from our experiments. Compared to the conventional brachytherapy techniques, the three methods studied in this work can produce more conformal dose distributions at an acceptable level of delivery time increase. With 15 min/fx delivery time, S-RSBT, D-RSBT and P-RSBT averagely increased the D90 (the minimum dose received by the hottest 90% of the tumor) by 17, 9 and 5 Gy compared to conventional interstitial plus intracavitary brachytherapy, whose D90 is 79 Gy. The best choice depends on the specified delivery time or quality requirement, as well as the complexity of building the equipment. Roughly speaking, among the three RSBT methods studied in this thesis, P-RSBT has the most complex applicators as well as the highest plan qualities. S-RSBT has the simplest applicators, and its plan qualities is generally better than D-RSBT with limited delivery time (/fx). With sufficient delivery time (~30 min/fx), D-RSBT may be considered as the best solution in the sense of balancing the complexity of applicators and the dose qualities.

This thesis describes experimental work performed (1998-2001) during the author's involvement with the Brachytherapy group at the Peter MacCallum Cancer Centre (PMCC), where he was employed by its Department of Physical Sciences and subsequent modeling and analytical studies. When PMCC added HDR brachytherapy to its radiation therapy practice, an existing operating suite was considered the ideal location for such procedures to be carried out. The integration of brachytherapy into the theatre environment was considered logical due to the relatively invasive nature of brachytherapy techniques and the availability of medical equipment. This thesis contains the detailed study of three key Research Questions involved in clinical aspects relating to quality assurance of an HDR brachytherapy practice. An investigative chapter is dedicated to the pursuit of each of the Research Questions. The first question asked… Is the novel approach to using modular shielding combined with time and distance constraints adequately optimized during HDR brachytherapy? In order to establish optimal clinical practices, this project evaluates the effectiveness of additional shielding added to the modular shielding system without modification of the previously determined time and distance constraints for PMCC staff, other patients, and member of the public. The DOSXYZnrc user code for the EGSnrc Monte Carlo radiation transport code has been used to model exposure pathways to strategic locations used for measurement in and around the operating theatre suite. Modeling allowed exposure pathways to various areas with the facility to be tested without the need to use real sources. The second Research Question asked… How well is dose anisotropy characterized in the near field range of the clinic's HDR 192Ir source? This study experimentally investigated the anisotropy of dose around a 192Ir HDR source in a water phantom using MOSFETs as relative dosimeters. In addition, modeling using the DOSRZnrc user code for the EGSnrc Monte Carlo radiation transport code was performed to provide a complete dose distribution consistent with the MOSFET measurements. Measurements performed for radial distances from 5 to 30 mm extend the range of measurements to 5 mm which has not been previously reported for this source construction. The third Research Question is aimed at the patient level. Is the dose delivered to in vivo dosimeters, located within critical anatomical structures near the prostate, within acceptable clinical tolerance for a large group of HDR prostate patients? An in vivo dosimetry technique employing TLDs to experimentally measure doses delivered to the urethra and rectum during HDR prostate brachytherapy was investigated. Urethral and rectal in vivo measurements for 56 patients have been performed in the initial fraction of four-fraction brachytherapy boost. In the absence of comparable in vivo data, the following local corrective action level was initially proposed: more than 50% of the prostatic urethra receiving a dose 10% beyond the urethral tolerance. The level for investigative action is considered from the analyses of dose differences between measured data and TPS calculation.

<p>Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.</p>

Dual Energy Computed Tomography (DECT) is an emerging technique that offers new possibilities to determine composition of tissues in clinical applications. Accurate knowledge of tissue composition is important for instance for brachytherapy (BT) treatment planning. However, the accuracy of CT numbers measured with contemporary clinical CT scanners is relatively low since CT numbers are affected by image artifacts. The aim of this work was to estimate the accuracy of CT numbers measured with the Siemens SOMATOM Definition Flash DECT scanner and the accuracy of the resulting volume or mass fractions calculated via the three material decomposition method. CT numbers of water, gelatin and a 3rd component (salt, hydroxyapatite or protein powder) mixtures were measured using Siemens SOMATOM Definition Flash DECT scanner. The accuracy of CT numbers was determined by (i) a comparison with theoretical (true) values and (ii) using different measurement conditions (configurations) and assessing the resulting variations in CT numbers. The accuracy of mass fractions determined via the three material decomposition method was estimated by a comparison with mass fractions measured with calibrated scales. The latter method was assumed to provide highly accurate results. It was found that (i) axial scanning biased CT numbers for some detector rows. (ii) large volume of air surrounding the measured region shifted CT numbers compared to a configuration where the region was surrounded by water. (iii) highly attenuating object shifted CT numbers of surrounding voxels. (iv) some image kernels caused overshooting and undershooting of CT numbers close to edges. The three material decomposition method produced mass fractions differing from true values by 8% and 15% for the salt and hydroxyapatite mixtures respectively. In this case, the analyzed CT numbers were averaged over a volumetric region. For individual voxels, the volume fractions were affected by statistical noise. The method failed when statistical noise was high or CT numbers of the decomposition triplet were similar. Contemporary clinical DECT scanners produced image artifacts that strongly affected the accuracy of the three material decomposition method; the Siemens’ image reconstruction algorithm is not well suited for quantitative CT. The three material decomposition method worked relatively well for averages of CT numbers taken from volumetric regions as these averages lowered statistical noise in the analyzed data.

Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.

A novel Y-90 liquid brachytherapy strategy is currently being studied for the treatment of osteosarcoma using a preclinical translational model in dogs to assess its potential efficacy and toxicity. In this study, dosimetry calculations are performed for Y-90 liquid brachytherapy in a dog with osteosarcoma using the Geant4 Monte Carlo code. A total of 611.83 MBq Y-90 radiopharmaceutical is administered via direct injections, and the in vivo distribution of Y-90 is assessed using a time-of-flight (TOF) PET/CT scanner. A patient-specific geometry is built using anatomical data obtained from CT images. The material properties of tumor and surrounding tissues are calculated based on a CT number - electron density calibration. The Y-90 distribution is sampled in Geant4 from PET images using a collapsing 3-D rejection technique to determine the decay sites. Dose distributions in the tumor bed and surrounding tissues are calculated demonstrating significant heterogeneity with multiple hot spots at the injection sites. Dose volume histograms show about 33.9 percent of bone and tumor and 70.2 percent of bone marrow and trabecular bone receive a total dose over 200 Gy; about 3.2 percent of bone and tumor and 31.0 percent of bone marrow and trabecular bone receive a total dose of over 1000 Gy. Y-90 liquid brachytherapy has the potential to be used as an adjuvant therapy or for palliation purposes. Future work includes evaluation of pharmacokinetics of the Y-90 radiopharmaceutical, calibration of PET/CT scanners for the direct quantitative assessment of Y-90 activity concentration, and assessment of efficacy of the Y-90 liquid brachytherapy strategy.

This dissertation explores beta dose profile of microspheres packed in arteries, various source geometries of 142Pr that can be used for therapeutic purpose, and dose backscatter factors for selected beta sources. A novel treatment method by injecting microspheres into feeding arteries of arteriovenous malformation (AVM) is under pre-clinical investigation. To optimize radiation dose to the clinically important area, i.e. arterial wall, preliminary dosimetric studies were needed. Monte Carlo calculations were performed for several geometries simulating arteries filled with microspheres packed by random packing methods. Arterial radii used in the simulation varied from 50 mm to 3 mm; microsphere radii varied from 10 mm to 0.7 mm. Dose varied significantly as a function of microsphere size, for constant arterial sizes. For the same sizes of arteries, significant dose increase was observed because of inter-artery exposure for large arteries (> 0.1 cm rad.) filled with large microspheres (> 0.03 cm rad.). Dose increase between small arteries (0.03 cm rad.) was less significant. The dose profiles of prototype 142Pr beta brachytherapy sources were calculated using MCNP 4C Monte Carlo code as well as dose point kernel (DPK) for selected cases. Dose profiles were similar to beta sources currently used indicating that 142Pr can substitute for current sources for certain cases and the DPK was closely matched with MCNP result. Backscattering of electrons is a prominent secondary effect in beta dosimetry. The backscattering is closely correlated with factors such as geometry of source and scattering material, and composition of scattering material. The backscattering factors were calculated for selected beta sources that are currently used as well as potentially useful sources for therapeutic purpose. The factors were calculated as a function of distance from the interface between water and scatterers. These factors were fit by a simple function for future incorporation into a DPK code. Backscattering effect was significant for short distance from the surface of interface between water and scattering material.

Tirtos Vilniaus universiteto Onkologijos institute gydytos pacientės, kurioms 1996 spalio mėnesį - 1998 kovo mėnesį buvo taikyta pooperacinė spindulinė terapija gama-neutronų šaltiniu gimdos kūno vėžio gydymui. Tyrimo tikslas: įvertinti gimdos kūno vėžio pooperacinio spindulinio gydymo gama-neutronų šaltiniu efektyvumą. Tyrimo uždaviniai: 1) Įvertinti vienerių, dvejų, trejų ir penkerių metų išgyvenamumą pacienčių grupėje. 2) Įvertinti vienerių, dvejų, trejų ir penkerių metų išgyvenamumą pacienčių amžiaus grupėje. 3) Įvertinti vienerių, dvejų, trejų ir penkerių metų išgyvenamumą pagal naviko charakteristikas: stadiją, morfologinį naviko tipą, naviko diferenciacijos laipsnį. 4) Įvertinti vienerių, dvejų, trejų ir penkerių metų išgyvenamumą pagal spindulinio gydymo charakteristikas: suminę židininę dozę, gydymo trukmę, laiką nuo diagnozės iki gydymo pradžios. Medžiaga ir metodai: naudotasi VU onkologijos institute esančiomis ambulatorinių kortelių ir vėžio registro duomenimis - iš viso 64 ligonių ligos istorijos: 52 pacientėms buvo taikyta pooperacinė ertmini gama-neutonų terapija + distancinė gamaterapija, 12 ertminė gama-neutronų terapija. Duomenų analizė atlikta naudojantis SPSS 11.0 versijos statistiniu duomenų analizės paketu. Skirtumui tarp grupių įvertinti taikytas Chi-kvadrato metodas. Visoms hipotezėms tikrinti taikytas reikšmingumo lygmuo 0,05. Išgyvenamumo analizė atlikta naudojant Kaplan - Meier ir išgyvenimo lentelių (life table) metodą. Rezultatai: Ertminės... [toliau žr. visą tekstą] / Women were treated with postoperative radiotherapy by using the gamma-neutrons’ source for treatment of endometrial cancer within the period from October 1, 1996 till March 1, 1998 at the Institute of Oncology of Vilnius University were surveyed in this study. Objective: to estimate the efficiency of endometrial cancer postoperative radiotherapy treatment by using the gamma-neutron source. Goals :1) to estimate one, two, three and five - year survival in a group of patients; 2) to estimate one, two, three and five - year survival according to the patients’ age; 3) to estimate one, two, three and five - year survival according to the tumor characteristics: morphologic tumor type, tumor differentiation degree; 4) to estimate one, two, three and five - year survival according to the radiotherapy characteristics: radiotherapy type, radiotherapy duration. Materials and Methods: The used materials consist of the case records collected at the Institute of Oncology of Vilnius University as well as of the data of the Cancer Register - overall 64 patients’ case records: 52 patients have had combined postoperative radiotherapy and 12 have had vaginal brachytherapy. The data were analyzed by the SPSS statistical package (Version 11.0 for Windows). The statistical assessment and analysis were performed with the qui-square (&#967;2), Kruscal-Wallis H test with values of p < 0,05 being defined as significant. The survival analysis was performed by using the Kaplan - Meier and life tables’... [to full text]

Brachytherapy is an important method of breast cancer treatment; however, improvements in both treatment planning and delivery are needed. The procedure involves insertion of catheters in the tumor site, which, in current practice, is prone to clinically significant error. In order to improve on contemporary catheter placement accuracy, integration of pre-operative imaging, supplemented by computerized surgical planning and mathematical optimization were used to develop and test an intra-operative immobilization and catheter guidance system. A custom-template specific to each patient with optimally-placed guide-holes for catheter insertion was designed and fabricated for use on phantom studies. Template creation is based on a virtual reality reconstruction of the patient's anatomy from computed tomography imaging. The template fits on the patient's breast, immobilizing the soft tissue, to provide pre-planned catheter insertion holes for guidance to the tumor site. Agar-based phantom and target models were used for quantitative validation of the template using computed tomography imaging for template planning and validation. Planned catheter tracks were compared to post-insertion image data and distance measurements from target location were used to create an error measure. Using the latest template design spanning multiple experiments resulted in a mean of 2.6 mm, 95%, CI =3.1-2.2, which is within the clinically acceptable range of 3 mm, as validated with our clinical collaborators. Validation of the brachytherapy template on phantom tissue produced clinically acceptable results. Use of a patient-specific template for breast brachytherapy is feasible and may improve the procedure accuracy and outcome. This work has been a proof-of-concept, providing evidence to support moving forward with the next phase of patient-specific breast template trials for use in brachytherapy. / Thesis (Master, Computing) -- Queen's University, 2011-10-03 15:17:07.933