Since its inception, Magnetic Resonance Imaging (MRI) has largely been used for qualitative diagnosis. Radiologists and physicians are increasingly becoming interested in quantitative assessments. The American College of Radiology (ACR) developed an accreditation program that incorporates tests pertaining to quantitative and qualitative analyses. As a result, sites often use the ACR procedure for daily quality assurance (QA) testing. The ACR accreditation program uses information obtained from clinical and phantom images to assess overall image quality of a scanner. For the phantom assessment, a human observer performs manual tests on T1 and T2-weighted volumes of the provided phantom. As these tests are tedious and time consuming, the primary goal of this research was to fully automate the procedure for QA purposes. The performance of the automated procedure was assessed by comparing the test results with the decisions made by human observers. The test results of the automated ACR QA procedure were well correlated with that of human observers. The automated ACR QA procedure takes approximately 5 minutes to complete. Upon program completion, the test results are logged in multiple text files. To this date, no QA procedure has been reported for Diffusion Tensor Imaging (DTI). Therefore, the secondary goal of this thesis was to develop a DTI QA procedure that assess two of the associated features used most in diagnosis, namely, diffusion anisotropy and the direction of primary diffusion. To this end, a physical phantom was constructed to model restricted diffusion, relative to axon size, using water-filled polytetrafluoroethylene (PTFE) microbore capillary tubes. Automated procedures were developed to test fractional anisotropy (FA) map contrast and capillary bundle (axon) orientation accuracy. / Master of Science

Yes / Objective To determine whether an immediate reporting service for musculoskeletal trauma reduces interpretation errors and positively impacts on patient referral pathways. Methods A pragmatic multicentre randomised controlled trial was undertaken. 1502 patients were recruited and randomly assigned to an immediate or delayed reporting arm and treated according to group assignment. Assessment was made of concordance in image interpretation between emergency department (ED) clinicians and radiology; discharge and referral pathways; and patient journey times. Results 1688 radiographic examinations were performed (1502 patients). 91 discordant interpretations were identified (n=91/1688; 5.4%) with a greater number of discordant interpretations noted in the delayed reporting arm (n=67/849, 7.9%). In the immediate reporting arm, the availability of a report reduced, but did not eliminate, discordance in interpretation (n=24/839, 2.9%). No significant difference in number of patients discharged, referred to hospital clinics or admitted was identified. However, patient ED recalls were significantly reduced (z=2.66; p=0.008) in the immediate reporting arm, as were the number of short-term inpatient bed days (5 days or less) (z=3.636; p<0.001). Patient journey time from ED arrival to discharge or admission was equivalent (z=0.79, p=0.432). Conclusion Immediate reporting significantly reduced ED interpretive errors and prevented errors that would require patient recall. However, immediate reporting did not eliminate ED interpretative errors or change the number of patients discharged, referred to hospital clinics or admitted overall. Advances in knowledge This is the first study to consider the wider impact of immediate reporting on the ED patient pathway as a whole and hospital resource usage.

No / The misinterpretation of radiographs is recognised as a key source of emergency department (ED) errors, regardless of clinician profession. This article compares ENP and medical staff accuracy in the interpretation of musculoskeletal trauma X-rays between immediate and delayed radiology reporting pathways. The data for this study was drawn from a larger pragmatic randomized controlled trial of immediate reporting. Patients were recruited and randomly assigned to immediate or delayed reporting arms and treated according to group assignment. Image interpretive accuracy between ED staff groups and arms was undertaken together with an assessment of the influence of immediate reporting on patient pathways and journey times. Six hundred and seventy-four radiographic examinations were performed (598 patients). There was a significant reduction in the interpretive errors in the immediate reporting arm for all ED clinicians (proportional difference = 4.2%; 95% CI [0.017,0.068]; p = 0.001), but no significant difference in proportion of interpretive errors was evident between ENPs and medical staff. Patient journey times, discharge and referral rates were not significantly different between study arms, although admission rates varied for medical staff collectively. ENP X-ray interpretation accuracy is comparable with that of medical staff, but immediate reporting was seen to reduce errors without increasing patient journey times.

Yes / Objectives: This study aimed to determine the impact on radiation dose and image quality of a new cardiac interventional X-ray system for trans-catheter aortic valve implantation (TAVI) patients compared to the previously-used cardiac X-ray system. Methods: Patient dose and image data were retrospectively collected from a Philips AlluraClarity (new) and Siemens Axion Artis (reference) X-ray system. Patient dose area product (DAP) and fluoroscopy duration of 41 patient cases from each X-ray system were compared using a Wilcoxon test. Ten patient aortograms from each X-ray system were scored by 32 observers on a continuous scale to assess the clinical image quality at the given phase of the TAVI procedure. Scores were dichotomised by acceptability and analysed using a Chi-squared test. Results: Significant reductions in patient dose (p<<0.001) were found for the new system with no significant change in fluoroscopy duration (p=0.052); procedure DAP reduced by 55%, fluoroscopy DAP by 48% and “cine” acquisition DAP by 61%. There was no significant difference between image quality scores of the two X-ray systems (p=0.06). Conclusions: The new cardiac X-ray system demonstrated a very significant reduction in patient dose with no loss of clinical image quality. Advances in Knowledge: The huge growth of TAVI may impact on the radiation exposure of cardiac patients and particularly on operators including anaesthetists; cumulative exposure of interventional cardiologists performing high volume TAVI over 30-40 years may be harmful. The Phillips Clarity upgrade including improved image enhancement and optimised X-ray settings significantly reduced radiation without reducing clinically acceptable image quality.

No / The purpose was to determine if an age based, local diagnostic reference level for paediatric skeletal surveys could be established using retrospective data. Methods: All children below two years of age referred for a primary skeletal survey as a result of suspected physical abuse during 2017 or 2018 (n ¼ 45) were retrospectively included from a large Danish university hospital. The skeletal survey protocol included a total of 33 images. Dose Area Product (DAP) and acquisition parameters for all images were recorded from the Picture Archival and Communication System (PACS) and effective dose was estimated. The 75th percentile for DAP was considered as the diagnostic reference level (DRL). Results: The 75th percentile for DAP was 314 mGy*cm2 , 520 mGy*cm2 and 779 mGy*cm2 for children <1 month, 1e11 months and 12 < 24 months of age respectively. However, only the age group 1e11 months had a sufficient number of children (n ¼ 27) to establish a local DRL. Thus, for the other groups the DAP result must be interpreted with caution. Effective dose was 0.19, 0.26 and 0.18 mSv for children <1, 1e11 months and 12 < 24 months of age respectively. Conclusion: For children between 1 and 11 months of age, a local diagnostic reference level of 520 mGy*cm2 was determined. This may be used as an initial benchmark for primary skeletal surveys as a result of suspected physical abuse for comparison and future discussion. Implications for practice: While the data presented reflects the results of a single department, the suggested diagnostic reference level may be used as a benchmark for other departments when auditing skeletal survey radiation dose.

Prostate cancer (PCa) is the second most common cancer diagnosis for men and the fifth leading cause of cancer-related death worldwide. A common treatment strategy for PCa is external beam radiation therapy (EBRT), where high doses of radiation are used to kill cancer cells. Recent developments in RT include maintaining acceptable side effects during intensified treatment over fewer treatment occasions (hypofractionation) and boosting the level of radiation to the gross tumor volume (GTV) visible on multiparametric magnetic resonance imaging (mpMRI) and positron emission tomography (PET). Without a histopathological (HP) reference, the dose distribution cannot be compared to the varying grades of aggressivity within the cancer, known as ISUP grade groups (IGGs). The aim of this master thesis project was to explore the dose distribution over IGGs using a gold standard HP reference and investigate the mitigating effects of rectal spacers, following a hypofractionated RT schedule with focal boosts. The dataset consists of 15 patients, planned for radical prostatectomy. These patients harbored high-risk disease (IGG ≥ 4) in the GTV. HP evaluations following surgery resulted in physical slices of the prostate, showing the location and IGG of lesions. EBRT treatment plans that combined an ultra-hypofractionation strategy with a boost to the GTV were made. The dose distributions were evaluated by dose volume histograms (DVHs) over the target volumes, organs at risks (OARs) and the lesions. Robust evaluations of targets and OARs were performed by recalculating doses following translations of the patient by 2 mm in all directions. Similarly, lesions were shifted by 2 mm in all directions with respect to the nominal dose plan to estimate the sensitivity to motion. The effects of the translations were assessed by examining the impact on the DVHs and percentage of passed clinical goals. Two viable dose plans for each patient were produced, one for a 10 mm spacer and one for 8 mm. Both plans fulfill all rectum goals. For the 10 mm plan, the average median dose (D50) was greater than the prescribed prostate dose (42.7 Gy) for all IGGs by atleast 1.1 Gy. The D50 of the higher grades (IGG 3, 4 and 5) were 47.5, 46.4 and 48.7 Gy, meaning that they were closer to the desired GTV dose 49.0 Gy than the prescribed prostate dose. This thesis project showed that it is possible to reach high GTV doses while sparing the OARs and that the higher IGGs received a higher dose than the lower grades. Examining rectal dose depending on different spacer thicknesses allowed us to recommend a spacer thickness that is safe to use, which can provide increased patient comfort while saving time and resources.

No description available.

Thesis (M. Tech. (Diagnostic Radiography)) Central University of Technology, Free State, 2014 / Over the past two decades, interventional radiology has been a fast developing field with great advances in technology in the diagnosing and treatment of patients. Interventional radiology procedures are minimally invasive and require little to no hospitalisation time. These procedures are fluoroscopically guided and serial runs are used for documentation, so they have the potential to deliver high doses to patients. Reports about deterministic skin reactions resulting from interventional radiology have become more and more prevalent from the early 1990s. Worldwide concern thus led to legislation for the limitation, justification and optimisation of these doses. Setting of diagnostic reference levels (DRLs) for these procedures is difficult, as they can be complex in nature and are often clinically open-ended. In the case where DRLs were used, they needed to be for a specific locality and had to be refined for the specific circumstances. Patients must be informed of the doses they will be receiving during diagnostic or interventional procedures before consent can be obtained from them. Little information on dose audits was available for South Africa at the time of the study, and it was decided to determine dose ranges at a local level. The research question of this study was: “What radiation doses do patients receive when undergoing vascular, diagnostic and interventional procedures in the interventional suites at a tertiary training hospital in the Free State?” The primary objective was to determine the doses and dose ranges to patients. A secondary objective was to identify specific high dose procedures to individual patients and to the population. A third objective was to investigate the factors influencing these doses. The data of patients who received procedures in two fluoroscopic rooms at the research site were documented over a three-year period. The dose area product (DAP) values were used to calculate skin dose. With the information gathered, dose ranges for frequently performed procedures were determined and specific high dose procedures to individuals and the population identified. Factors influencing the dose were also investigated. This included the relationship of the level of technology, a VI patient’s BMI and practitioners’ level of experience on dose as the research site was a training facility. The results indicated that both diagnostic and interventional procedures have the potential to deliver high doses, as was evident with the isolated occurrences where the response threshold for deterministic effects was exceeded. Most of the locally performed procedures delivered lower or on par radiation dose, compared to values in the literature. Increased BMI values of patients can negatively influence doses received. The level of a practitioner’s experience also plays a vital role in the dose that the patient will receive. Specific recommendations and the implementing of a dose optimisation protocol are proposed to reduce and optimise doses at the research site. This dose optimisation programme will create greater awareness about radiation dose and effects, follow-up procedures and dose reduction methods amongst role-payers. Key words: interventional radiology; limitation, justification and optimisation of radiation dose; deterministic effects; radiation dose awareness

The historical development, current practice, and the future of interventional neuroradiology are intricately linked to the advancements in the imaging and devices used for neuroendovascular treatments. This thesis explores the advanced imaging potential of the C-arm imaging systems used in the neurointerventional suite and investigates the initial clinical experience with a new flow diverter device to treat the intracranial aneurysms. A cohort of aneurysmal SAH patients who developed delayed cerebral ischaemia (DCI) were prospectively studied with a new parenchymal blood volume (PBV) research protocol C-arm CT examination concurrent with a magnetic resonance (MR) imaging examination that included perfusion and diffusion weighted sequences. Using a robust quantitative volume-of-interest analysis, it was demonstrated that C-arm CT PBV measurements are in agreement with MR-PWI CBV and CBF, and the PBV represents a composite perfusion parameter with both blood-flow (&asymp;60&percnt;) and blood-volume (&asymp;40&percnt;) weightings. Subsequently, using a voxel-wise ROC curve analysis and MR-DWI, it was shown that using optimal thresholds, C-arm CT PBV measurements allow reliable demarcation of the irreversibly infarcted parenchyma. For evaluation of ischaemic parenchyma, the PBV measurements were reliable for moderate-to-severe ischaemia but were prone to underestimate the mild-to-moderate ischaemia. A catalogue of reference mean PBV measurements was then created for various anatomical regions encompassing the whole brain after excluding any locations with ongoing ischaemia or infarction. Next, using an ROI-based analysis of the C-arm CT projection data, steady-state contrast concentration assumption underlying the PBV calculations was investigated. It was demonstrated that for clinical scans, the ideal steady-state assumption is not fully met, however, for a large majority of C-arm CT examinations the temporal characteristics of TDCs closely approximate the expected ideal steady-state. The degree to which the TDC of a C-arm CT scan approximates the ideal steady-state was found to influence the resulting PBV measurements and their agreement to MR-CBV. Moreover, the temporal characteristics of TDCs showed inter-subject variation. Finally, the C-arm CT cross-sectional soft tissue images were demonstrated to be of adequate quality for the assessment of ventricles and for the detection of procedural vessel rupture. These findings advance the understanding of the nature of PBV parameter, establish the optimal PBV thresholds for infarction, provide reference PBV measurements, and highlight the limitations of C-arm CT PBV imaging. The work is of considerable clinical significance and has implications for implementation of C-arm CT PBV imaging in the interventional suite for management of patients with acute brain ischaemia. In regards to the initial clinical experience with the flow diversion treatment of intracranial aneurysms, the procedural, angiographic, and clinical outcomes were studied. Several pertinent technical and clinical issues were highlighted for this new treatment approach. Based on the observations made during this work, a new grading schema was then developed to monitor the angiographic outcomes after flow diversion treatment. Using the angiographic data for patients treated with FD, the new grading schema was demonstrated to be sufficiently sensitive to register gradual aneurysm occlusion and evaluate parent artery patency, with an excellent inter-rater reliability and applicability to various aneurysm morphologies. This work (largest multi-centre series at the time of its publication) informed the interventional neuroradiology community about the safety, efficacy, and outcomes of flow diversion treatment. Additionally, it provided a sensitive and reliable scale to evaluate the angiographic outcomes after flow diversion treatment, in both research and clinical practice.

<p>The developments of highly conformal and precise radiation therapy techniques promote the necessity of more accurate treatment target localization and tracking. On-board imaging techniques, especially the x-ray based techniques, have found a great popularity nowadays for on-board target localization and tracking. With an objective to improve the accuracy of on-board imaging for lung cancer patients, the dissertation work focuses on the investigations of using limited-angle on-board x-ray projections for image guidance. The limited-angle acquisition enables scan time and imaging dose reduction and improves the mechanical clearance of imaging.</p><p>First of all, the dissertation developed a phase-matched digital tomosynthesis (DTS) technique using limited-angle (<=30 deg) projections for lung tumor localization. This technique acquires the same traditional motion-blurred on-board DTS image as the 3D-DTS technique, but uses the planning 4D computed tomography (CT) to synthesize a phase-matched reference DTS to register with the on-board DTS for tumor localization. Of the 324 different scenarios simulated using the extended cardiac torso (XCAT) digital phantom, the phase-matched DTS technique localizes the 3D target position with an localization error of 1.07 mm (± 0.57 mm) (average ± standard deviation (S.D.)). Similarly, for the total 60 scenarios evaluated using the computerized imaging reference system (CIRS) 008A physical phantom, the phase-matched DTS technique localizes the 3D target position with an average localization error of 1.24 mm (± 0.87 mm). In addition to the phantom studies, preliminary clinical cases were also studied using imaging data from three lung cancer patients. Using the localization results of 4D cone beam computed tomography (CBCT) as `gold-standard', the phase-matched DTS techniques localized the tumor to an average localization error of 1.5 mm (± 0.5 mm). </p><p>The phantom and patient study results show that the phase-matched DTS technique substantially improved the accuracy of moving lung target localization, as compared to the 3D-DTS technique. The phase-matched DTS technique can provide accurate lung target localizations like 4D-DTS, but with much reduced imaging dose and scan time. The phase-matched DTS technique is also found more robust, being minimally affected by variations of respiratory cycle lengths, fractions of respiration cycle contained within the DTS scan and the scan directions, which potentially enables quasi-instantaneous (within a sub-breathing cycle) moving target verification during radiation therapy, preferably arc therapy.</p><p>Though the phase-matched DTS technique can provide accurate target localization under normal scenarios, its accuracy is limited when the patient on-board breathing experiences large variations in motion amplitudes. In addition, the limited-angle based acquisition leads to severe structural distortions in DTS images reconstructed by the current clinical gold-standard Feldkamp-Davis-Kress (FDK) reconstruction algorithm, which prohibit accurate target deformation tracking, delineation and dose calculation. </p><p>To solve the above issues, the dissertation further developed a prior knowledge based image estimation technique to fundamentally change the landscape of limited-angle based imaging. The developed motion modeling and free-form deformation (MM-FD) method estimates high quality on-board 4D-CBCT images through applying deformation field maps to existing prior planning 4D-CT images. The deformation field maps are solved using two steps: first, a principal component analysis based motion model is built using the planning 4D-CT (motion modeling). The deformation field map is constructed as an optimized linear combination of the extracted motion modes. Second, with the coarse deformation field maps obtained from motion modeling, a further fine-tuning process called free-form deformation is applied to further correct the residual errors from motion modeling. Using the XCAT phantom, a lung patient with a 30 mm diameter tumor was simulated to have various anatomical and respirational variations from the planning 4D-CT to on-board 4D-CBCTs, including respiration amplitude variations, tumor size variations, tumor average position variations, and phase shift between tumor and body respiratory cycles. The tumors were contoured in both the estimated and the `ground-truth' on-board 4D-CBCTs for comparison. 3D volume percentage error (VPE) and center-of-mass error (COME) were calculated to evaluate the estimation accuracy of the MM-FD technique. For all simulated patient scenarios, the average (± S.D.) VPE / COME of the tumor in the prior image without image estimation was 136.11% (± 42.76%) / 15.5 mm (± 3.9 mm). Using orthogonal-view 30 deg scan angle, the average VPE/COME of the tumors in the MM-FD estimated on-board images was substantially reduced to 5.22% (± 2.12%) / 0.5 mm (± 0.4 mm). </p><p>In addition to XCAT simulation, CIRS phantom measurements and actual patient studies were also performed. For these clinical studies, we used the normalized cross-correlation (NCC) as a new similarity metric and developed an updated MMFD-NCC method, to improve the robustness of the image estimation technique to the intensity mismatches between CT and CBCT imaging systems. Using 4D-CBCT reconstructed from fully-sampled on-board projections as `gold-standard', for the CIRS phantom study, the average (± S.D.) VPE / COME of the tumor in the prior image and the tumors in the MMFD-NCC estimated images was 257.1% (± 60.2%) / 10.1 mm (± 4.5 mm) and 7.7% (± 1.2%) / 1.2 mm (± 0.2mm), respectively. For three patient cases, the average (± S.D.) VPE / COME of tumors in the prior images and tumors in the MMFD-NCC estimated images was 55.6% (± 45.9%) / 3.8 mm (± 1.9 mm) and 9.6% (± 6.1%) / 1.1 mm (± 0.5 mm), respectively. With the combined benefits of motion modeling and free-form deformation, the MMFD-NCC method has achieved highly accurate image estimation under different scenarios. </p><p>Another potential benefit of on-board 4D-CBCT imaging is the on-board dose calculation and verification. Since the MMFD-NCC estimates the on-board 4D-CBCT through deforming prior 4D-CT images, the 4D-CBCT inherently has the same image quality and Hounsfield unit (HU) accuracy as 4D-CT and therefore can potentially improve the accuracy of on-board dose verification. Both XCAT and CIRS phantom studies were performed for the dosimetric study. Various inter-fractional variations featuring patient motion pattern change, tumor size change and tumor average position change were simulated from planning CT to on-board images. The doses calculated on the on-board CBCTs estimated by MMFD-NCC (MMFD-NCC doses) were compared to the doses calculated on the `gold-standard' on-board images (gold-standard doses). The absolute deviations of minimum dose (DDmin), maximum dose (DDmax), mean dose (DDmean) and prescription dose coverage (DV100%) of the planning target volume (PTV) were evaluated. In addition, 4D on-board treatment dose accumulations were performed using 4D-CBCT images estimated by MMFD-NCC in the CIRS phantom study. The accumulated doses were compared to those measured using optically stimulated luminescence (OSL) detectors and radiochromic films. </p><p>The MMFD-NCC doses matched very well with the gold-standard doses. For the XCAT phantom study, the average (± S.D.) DDmin, DDmax, DDmean and DV100% (values normalized by the prescription dose or the total PTV volume) between the MMFD-NCC PTV doses and the gold-standard PTV doses were 0.3% (± 0.2%), 0.9% (± 0.6%), 0.6% (± 0.4%) and 1.0% (± 0.8%), respectively. Similarly, for the CIRS phantom study, the corresponding values between the MMFD-NCC PTV doses and the gold-standard PTV doses were 0.4% (± 0.8%), 0.8% (± 1.0%), 0.5% (± 0.4%) and 0.8% (± 0.8%), respectively. For the 4D dose accumulation study, the average (± S.D.) absolute dose deviation (normalized by local doses) between the accumulated doses and the OSL measured doses was 3.0% (± 2.4%). The average gamma index (3%/3mm) between the accumulated doses and the radiochromic film measured doses was 96.1%. The MMFD-NCC estimated 4D-CBCT enables accurate on-board dose calculation and accumulation for lung radiation therapy under different scenarios. It can potentially be valuable for treatment quality assessment and adaptive radiation therapy.</p><p>However, a major limitation of the estimated 4D-CBCTs above is that they can only capture inter-fractional patient variations as they were acquired prior to each treatment. The intra-treatment patient variations cannot be captured, which can also affect the treatment accuracy. In light of this issue, an aggregated kilo-voltage (kV) and mega-voltage (MV) imaging scheme was developed to enable intra-treatment imaging. Through using the simultaneously acquired kV and MV projections during the treatment, the MMFD-NCC method enabled 4D-CBCT estimation using combined kV and MV projections. </p><p>For all XCAT-simulated patient scenarios, the average (± S.D.) VPE / COME of the tumor in the prior image and tumors in the MMFD-NCC estimated images (using kV + open field MV) was 136.11% (± 42.76%) / 15.5 mm (± 3.9 mm) and 4.5% (± 1.9%) / 0.3 mm (± 0.4 mm), respectively. In contrast, the MMFD-NCC estimation using kV + beam's eye view (BEV) MV projections yielded results of 4.3% (± 1.5%) / 0.3 mm (± 0.3 mm). The kV + BEV MV aggregation can estimate the target as accurately as the kV + open field MV aggregation. The impact of this study is threefold: 1. the kV and MV projections can be acquired at the same time. The imaging time will be cut to half as compared to the cases which use kV projections only. 2. The kV and MV aggregation enables intra-treatment imaging and target tracking, since the MV projections can be the side products of the treatment beams (BEV MV). 3. As the BEV MV projections originate from the treatment beams, there will be no extra MV imaging dose to the patient.</p><p>The above introduced 4D-CBCT estimation techniques were all based on limited-angle acquisition. Though limited-angle acquisition enables substantial scan time and dose reduction as compared to the full-angle scan, it is still not real-time and cannot provide `cine' imaging, which refers to the instantaneous imaging with negligible scan time and imaging dose. Cine imaging is important in image guided radiation therapy practice, considering the respirational variations may occur quickly and frequently during the treatment. For instance, the patient may experience a breathing baseline shift after every respiratory cycle. The limited-angle 4D-CBCT approach still requires a scan time of multiple respiratory cycles, which will not be able to capture the baseline shift in a timely manner. </p><p>In light of this issue, based on the previously developed MMFD-NCC method, an AI-FD-NCC method was further developed to enable quasi-cine CBCT imaging using extremely limited-angle (<=6 deg) projections. Using pre-treatment 4D-CBCTs acquired just before the treatment as prior information, AI-FD-NCC enforces an additional prior adaptive constraint to estimate high quality `quasi-cine' CBCT images. Two on-board patient scenarios: tumor baseline shift and continuous motion amplitude change were simulated through the XCAT phantom. Using orthogonal-view 6 deg projections, for the baseline shift scenario, the average (± S.D.) VPE / COME of the tumors in the AI-FD-NCC estimated images was 1.3% (± 0.5%) / 0.4 mm (± 0.1 mm). For the amplitude variation scenario, the average (± S.D.) VPE / COME of the tumors in the AI-FD-NCC estimated images was 1.9% (± 1.1%) / 0.5 mm (± 0.2 mm). The impact of this study is three-fold: first, the quasi-cine CBCT technique enables actual real-time volumetric tracking of tumor and normal tissues. Second, the method enables real-time tumor and normal tissues dose calculation and accumulation. Third, the high-quality volumetric images obtained can potentially be used for real-time adaptive radiation therapy.</p><p>In summary, the dissertation work uses limited-angle on-board x-ray projections to reconstruct/estimate volumetric images for lung tumor localization, delineation and dose calculation. Limited-angle acquisition reduces imaging dose, scan time and improves imaging mechanical clearance. Using limited-angle projections enables continuous, sub respiratory-cycle tumor localization, as validated in the phase-matched DTS study. The combination of prior information, motion modeling, free-form deformation and limited-angle on-board projections enables high-quality on-board 4D-CBCT estimation, as validated by the MM-FD / MMFD-NCC techniques. The high-quality 4D-CBCT not only can be applied for accurate target localization and delineation, but also can be used for accurate treatment dose verification, as validated in the dosimetric study. Through aggregating the kV and MV projections for image estimation, intra-treatment 4D-CBCT imaging was also proposed and validated for its feasibility. At last, the introduction of more accurate prior information and additional adaptive prior knowledge constraints also enables quasi-cine CBCT imaging using extremely-limited angle projections. The dissertation work contributes to lung on-board imaging in many aspects with various approaches, which can be beneficial to the future lung image guided radiation therapy practice.</p> / Dissertation