Currently in our clinic, a mega-voltage cone beam computed tomography (MVCBCT) scan is performed before each treatment for patient localization. For non-small cell lung cancer (NSCLC) patients, a strain gauge is used as an external surrogate to indicate tumor motion in both the planning stage and the treatment stage. However, it is likely that the amplitude of tumor motion varies between treatment fractions without a corresponding change in the surrogate signal. Motion amplitude larger than what was planned may underdose the tumor and overexpose normal tissues. The overall objective of this project is to extend the capabilities of MVCBCT for respiratory motion management by taking advantage of 2D projection images. First, a new method was developed to detect ipsi-lateral hemi-diaphragm apex (IHDA) motion along superior-inferior (SI) direction in 3D. Then a respiratory correlated reconstruction method was implemented and verified. This method is able to create MVCBCT volume in the full exhale (FE) and the full inhale (FI) phases, respectively. The diaphragm to tumor motion ratio (DTMR) was derived by quantifying the absolute position of the tumor and IHDA in these two volumes. The DTMR and the extracted IHDA motion were further used to calibrate the strain gauge signal. Second, an organ motion detection approach was developed, in which the detection is converted into an optimal interrelated surface detection problem. The framework was first applied to tumor motion extraction, which enables accurate detection for large tumors (with a diameter not smaller than 1.9cm). The framework was then applied to lung motion extraction and the extracted lung motion model was used to create a series of displacement vector fields for a motion compensated (MC) reconstruction. The accuracy of both tumor extraction and the MC approach was validated, which shows their clinical feasibility. Last but not least, a novel enhancement framework was developed. The aim of this approach is to eliminate the overlapping tissues and organs in the CBCT projection images. Though scattering and noise is the major problem, the proposed method is able to achieve enhanced projection images with a higher contrast to noise ratio (CNR) without compromising detection accuracy on tumors and IHDA.

As alterações volumétricas da cavidade oral, nasal e espaço faríngeo após a cirurgia ortognática, têm sido objetivo de muitos estudos, uma vez que, essas alterações dependem da direção e magnitude da movimentação dos segmentos ósseos, porém, poucos são os trabalhos que combinam os diferentes métodos para a avaliação da nasofaringe. O objetivo deste estudo foi correlacionar o espaço aéreo faríngeo em pacientes com fissura labiopalatina, submetidos à cirurgia ortognática com avanço de maxila e/ou recuo de mandíbula, por meio da análise do volume e área seccional mínima utilizando imagens de tomografia computadorizada de feixe cônico e pela rinomanometria anterior modificada (técnica fluxo-pressão) no pré e pós-operatório de um ano da cirurgia ortognática. Desse modo, a amostra foi composta por 41 indivíduos, que foram avaliados no pré-operatório e no pós-operatório, na qual, avaliou-se a área seccional mínima pela rinomanometria anterior modificada expressos em mm2 e pelas imagens de tomografia de feixe cônico, que foram importadas em DICOM e avaliadas pelo software Dolphin Imaging 11.0, obtendo os valores numéricos de volume (V), expressos em cm3, bem como a área seccional mínima, expressa em mm2. Notou-se que, em todas as variáveis, houve aumento médio dos valores no pós-operatório em relação ao pré-operatório. Além disso, notouse uma diferença estatisticamente significante ao comparar os resultados dos volumes e da área seccional mínima da área nasofaríngea no pré e pós-operatório pelo software Dolphin Imaging 11.0 ao aplicar o Teste de Wilcoxon. Observou-se também, o aumento discreto da área nasofaríngea avaliada pela rinomanometria, no préoperatório de 105,9 mm2 para 107,1 mm2 no pós-operatório, mas sem diferença estatisticamente significante com p=0,493 pelo Teste de Wilcoxon. E ao comparar a ASM pela TCFC (ASMD) e pela rinomanometria (notou-se diferença estatística (p= 0,033) pelo Teste de Wilcoxon. Por conseguinte, concluiu-se que, existe diferença estatisticamente significante entre a área seccional mínima obtida da TCFC com a rinomanometria pela técnica de fluxo-pressão. / The volumetric changes of the oral cavity, nasal cavity and pharyngeal space after orthognathic surgery have been the objective of many studies, since these alterations depend on the direction and magnitude of the movement of the bone segments, however, there are few studies that combine the different methods for evaluating the nasopharynx. The objective of this study was to correlate the pharyngeal air space in patients with cleft lip and palate submitted to orthognathic surgery with maxillary advancement and / or mandible retreatment, by means of volume analysis and minimum sectional area using conical beam computed tomography by modified anterior rhinomanometry (flow-pressure technique) in the pre- and postoperative year of orthognathic surgery. Thus, the sample consisted in 41 individuals, which were evaluated preoperatively and postoperatively, in which the minimum sectional area was determined by modified anterior rhinomanometry expressed in mm2 and by conical beam tomography images, which were imported into DICOM and evaluated by Dolphin Imaging 11.0 software, obtaining the numerical values of volume (V), expressed in cm3, as well as the minimum sectional area, expressed in mm2. It was observed that, in all variables, there was an average increase in postoperative values in relation to the preoperative period. In addition, a statistically significant difference was observed when comparing the results of the volumes and the minimum sectional area of the nasopharyngeal area in the pre and postoperative period by the Dolphin Imaging 11.0 software when applying the Wilcoxon Test. It was also observed a discrete increase in the nasopharyngeal area evaluated by rhinomanometry, in the preoperative period from 105.9 mm2 to 107.1 mm2 postoperatively, but without a statistically significant difference with p = 0.493 by the Wilcoxon test. When comparing ASM by CBCT (ASMD) and rhinomanometry (a statistical difference (p = 0.033) was noted by the Wilcoxon test. Therefore, it was concluded that there is a statistically significant difference between the minimum sectional area obtained from the CBCT with rhinomanometry.

<p>In this project several tests were performed to evaluate the performance of an On-Board Imager® (OBI) mounted on a clinical linear accelerator. The measurements were divided into three parts; geometric accuracy, image registration and couch shift accuracy, and image quality. A cube phantom containing a radiation opaque marker was used to study the agreement with treatment isocenter for both kV-images and cone-beam CT (CBCT) images. The long term stability was investigated by acquiring frontal and lateral kV images twice a week over a 3 month period. Stability in vertical and longitudinal robotic arm motion as well as the stability of the center-of-rotation was evaluated. Further, the agreement of kV image and CBCT center with MV image center was examined.</p><p>A marker seed phantom was used to evaluate and compare the three applications in image registration; 2D/2D, 2D/3D and 3D/3D. Image registration using kV-kV image sets were compared with MV MV and MV-kV image sets. Further, the accuracy in 2D/2D matches with images acquired at non-orthogonal gantry angles was evaluated. The image quality in CBCT images was evaluated using a Catphan® phantom. Hounsfield unit (HU) uniformity and linearity was compared with planning CT. HU accuracy is crucial for dose verification using CBCT data.</p><p>The geometric measurements showed good long term stability and accurate position reproducibility after robotic arm motions. A systematic error of about 1 mm in lateral direction of the kV-image center was detected. A small difference between kV and CBCT center was observed and related to a lateral kV detector offset. The vector disagreement between kV- and MV-image centers was  2 mm at some gantry angles. Image registration with the different match applications worked sufficiently. 2D/3D match was seen to correct more accurately than 2D/2D match for large translational and rotational shifts. CBCT images acquired with full-fan mode showed good HU uniformity but half fan images were less uniform. In the soft tissue region the HU agreement with planning CT was reasonable while a larger disagreement was observed at higher densities. This work shows that the OBI is robust and stable in its performance. With regular QC and calibrations the geometric precision of the OBI can be maintained within 1 mm of treatment isocenter.</p>

<p>Contemporary algorithms employed for reconstruction of 3D volumes from helical cone beam projections are so called non-exact algorithms. This means that the reconstructed volumes contain artifacts irrespective of the detector resolution and number of projection angles employed in the process. In this thesis, three iterative schemes for suppression of these so called cone artifacts are investigated.</p><p>The first scheme, iterative weighted filtered backprojection (IWFBP), is based on iterative application of a non-exact algorithm. For this method, artifact reduction, as well as spatial resolution and noise properties are measured. During the first five iterations, cone artifacts are clearly reduced. As a side effect, spatial resolution and noise are increased. To avoid this side effect and improve the convergence properties, a regularization procedure is proposed and evaluated.</p><p>In order to reduce the cost of the IWBP scheme, a second scheme is created by combining IWFBP with the so called ordered subsets technique, which we call OSIWFBP. This method divides the projection data set into subsets, and operates sequentially on each of these in a certain order, hence the name “ordered subsets”. We investigate two different ordering schemes and number of subsets, as well as the possibility to accelerate cone artifact suppression. The main conclusion is that the ordered subsets technique indeed reduces the number of iterations needed, but that it suffers from the drawback of noise amplification.</p><p>The third scheme starts by dividing input data into high- and low-frequency data, followed by non-iterative reconstruction of the high-frequency part and IWFBP reconstruction of the low-frequency part. This could open for acceleration by reduction of data in the iterative part. The results show that a suppression of artifacts similar to that of the IWFBP method can be obtained, even if a significant part of high-frequency data is non-iteratively reconstructed.</p>

Megavoltage computed tomography (MVCT) and megavoltage cone beam computed tomography can be used for visualizing anatomical structures prior to radiation therapy treatments to assist in patient setup and target localization. These systems provide images using the same beam used for patient treatment, however their image contrast is limited by the low detective quantum efficiency (DQE) of the detectors currently available. By using higher DQE thick, segmented cadmium tungstate detectors we can improve the system contrast. This in turn would permit enhanced soft tissue visualization, allowing MVCT to be more useful. This thesis describes the evaluation of a prototype MVCT system that uses thick, segmented detectors. The system was found to be able to easily visualize a 15 mm diameter 1.5% contrast target with 2 cGy of radiation dose delivered. This system could become the basis for improved commercial MVCT systems. / Medical Physics

Contemporary algorithms employed for reconstruction of 3D volumes from helical cone beam projections are so called non-exact algorithms. This means that the reconstructed volumes contain artifacts irrespective of the detector resolution and number of projection angles employed in the process. In this thesis, three iterative schemes for suppression of these so called cone artifacts are investigated. The first scheme, iterative weighted filtered backprojection (IWFBP), is based on iterative application of a non-exact algorithm. For this method, artifact reduction, as well as spatial resolution and noise properties are measured. During the first five iterations, cone artifacts are clearly reduced. As a side effect, spatial resolution and noise are increased. To avoid this side effect and improve the convergence properties, a regularization procedure is proposed and evaluated. In order to reduce the cost of the IWBP scheme, a second scheme is created by combining IWFBP with the so called ordered subsets technique, which we call OSIWFBP. This method divides the projection data set into subsets, and operates sequentially on each of these in a certain order, hence the name “ordered subsets”. We investigate two different ordering schemes and number of subsets, as well as the possibility to accelerate cone artifact suppression. The main conclusion is that the ordered subsets technique indeed reduces the number of iterations needed, but that it suffers from the drawback of noise amplification. The third scheme starts by dividing input data into high- and low-frequency data, followed by non-iterative reconstruction of the high-frequency part and IWFBP reconstruction of the low-frequency part. This could open for acceleration by reduction of data in the iterative part. The results show that a suppression of artifacts similar to that of the IWFBP method can be obtained, even if a significant part of high-frequency data is non-iteratively reconstructed.

In this project several tests were performed to evaluate the performance of an On-Board Imager® (OBI) mounted on a clinical linear accelerator. The measurements were divided into three parts; geometric accuracy, image registration and couch shift accuracy, and image quality. A cube phantom containing a radiation opaque marker was used to study the agreement with treatment isocenter for both kV-images and cone-beam CT (CBCT) images. The long term stability was investigated by acquiring frontal and lateral kV images twice a week over a 3 month period. Stability in vertical and longitudinal robotic arm motion as well as the stability of the center-of-rotation was evaluated. Further, the agreement of kV image and CBCT center with MV image center was examined. A marker seed phantom was used to evaluate and compare the three applications in image registration; 2D/2D, 2D/3D and 3D/3D. Image registration using kV-kV image sets were compared with MV MV and MV-kV image sets. Further, the accuracy in 2D/2D matches with images acquired at non-orthogonal gantry angles was evaluated. The image quality in CBCT images was evaluated using a Catphan® phantom. Hounsfield unit (HU) uniformity and linearity was compared with planning CT. HU accuracy is crucial for dose verification using CBCT data. The geometric measurements showed good long term stability and accurate position reproducibility after robotic arm motions. A systematic error of about 1 mm in lateral direction of the kV-image center was detected. A small difference between kV and CBCT center was observed and related to a lateral kV detector offset. The vector disagreement between kV- and MV-image centers was  2 mm at some gantry angles. Image registration with the different match applications worked sufficiently. 2D/3D match was seen to correct more accurately than 2D/2D match for large translational and rotational shifts. CBCT images acquired with full-fan mode showed good HU uniformity but half fan images were less uniform. In the soft tissue region the HU agreement with planning CT was reasonable while a larger disagreement was observed at higher densities. This work shows that the OBI is robust and stable in its performance. With regular QC and calibrations the geometric precision of the OBI can be maintained within 1 mm of treatment isocenter.

No description available.

<p>Cone beam computed tomography (CBCT) is a 3D x-ray imaging technique in which the x-ray beam is transmitted to an object with wide beam geometry producing a 2D image per projection. Due to its faster image acquisition time, wide coverage length per scan, and fewer motion artifacts, the CBCT system is rapidly replacing the conventional CT system and becoming popular in diagnostic and therapeutic radiology. However, there are few studies performed in CBCT dosimetry because of the absence of a standard dosimetric protocol for CBCT. Computed tomography dose index (CTDI), a standardized metric in conventional CT dosimetry, or direct organ dose measurements have been limitedly used in the CBCT dosimetry.</p> <p>This dissertation investigated the CBCT dosimetry from the CTDI method to the organ, effective dose, risk estimations with physical measurements and Monte Carlo (MC) simulations.</p> <p>An On-Board Imager (OBI, Varian Medical Systems, Palo Alto, CA) was used to perform old and new CBCT scan protocols. The new CBCT protocols introduced both partial and full angle scan modes while the old CBCT protocols only used the full angle mode. A metal-oxide-semiconductor-field-effect transistor (MOSFET) and an ion chamber were employed to measure the cone beam CTDI (CTDI_CB) in CT phantoms and organ dose in a 5-year-old pediatric anthropomorphic phantom. Radiochromic film was also employed to measure the axial dose profiles. A point dose method was used in the CTDI estimation.</p> <p>The BEAMnrc/EGSnrc MC system was used to simulate the CBCT scans; the MC model of the OBI x-ray tube was built into the system and validated by measurements characterizing the cone beam quality in the aspects of the x-ray spectrum, half value layer (HVL) and dose profiles for both full-fan and half-fan modes. Using the validated MC model, CTDI_CB, dose profile integral (DPI), cone beam dose length product (DLP_CB), and organ doses were calculated with voxelized MC CT phantoms or anthropomorphic phantoms. Effective dose and radiation risks were estimated from the organ dose results.</p> <p>The CTDI_CB of the old protocols were found to be 84 and 45 mGy for standard dose, head and body protocols. The CTDI_CB of the new protocols were found to be 6.0, 3.2, 29.0, 25.4, 23.8, and 7.7 mGy for the standard dose head, low dose head, high quality head, pelvis, pelvis spotlight, and low dose thorax protocols respectively. The new scan protocols were found to be advantageous in reducing the patient dose while offering acceptable image quality.</p> <p>The mean effective dose (ED) was found to be 37.8 ±0.7 mSv for the standard head and 8.1±0.2 mSv for the low dose head protocols (old) in the 5-year-old phantom. The lifetime attributable risk (LAR) of cancer incidence ranged from 23 to 144 cases per 100,000 exposed persons for the standard-dose mode and from five to 31 cases per 100,000 exposed persons for the low-dose mode. The relative risk (RR) of cancer incidence ranged from 1.003 to 1.054 for the standard-dose mode and from 1.001 to 1.012 for the low-dose mode.</p> <p>The MC method successfully estimated the CTDI_CB, organ and effective dose despite the heavy calculation time. The point dose method was found to be capable of estimating the CBCT dose with reasonable accuracy in the clinical environment.</p> / Dissertation

Modern image-guided surgery aids minimally-invasive, high-precision procedures that increase efficacy of treatment. This thesis investigates two research aims to improve precision and integration of intraoperative cone-beam CT (CBCT) imaging in guidance of head and neck (H&N) surgery. First, marker configurations were examined to identify arrangements that minimize target registration error (TRE). Best arrangements minimized the distance between the configuration centroid and surgical target while maximizing marker separation. Configurations of few markers could minimized TRE with more markers providing improved uniformity. Second, an algorithm for automatic registration of image and world reference frames was pursued to streamline integration of CBCT with real-time tracking and provide automatic updates per scan. Markers visible to the tracking and imaging systems are automatically co-localized and registered with equivalent accuracy and superior reproducibility compared to conventional registration. Such work helps the implementation of CBCT in H&N surgery to maximize surgical precision and exploit intraoperative image guidance.