A prototype electrostatic imager has been developed for megavoltage portal imaging in radiation therapy. The imager utilizes amorphous selenium (a-Se) with a front metal plate as the imager receptor and a high resolution voltmeter probe for image readout. Imaging characteristics of a-Se have been investigated theoretically through Monte Carlo simulations, and experimentally by measuring radiation discharging curves and phantom tests. The results of this study have shown that the prototype imager has high sensitivity, good spatial resolution and low noise level. Our study also reveals the potential of electrostatic imaging with metal/a-Se in megavoltage imaging. / Two computer algorithms have also been developed for automatic segmentation and contrast-enhancement of digital portal images, and for radiation field shape verification. Based on a priori knowledge of the properties of portal images, the segmentation and contrast-enhancement algorithm employs multiple criteria and dynamic reasoning to achieve optimal segmentations of individual images, and has been proved to be accurate, robust and fast. The algorithm for radiation field shape verification is an adaptation of the chamfer matching technique to a specific application: matching closed contours. By incorporating geometric features of the radiation field and using a simple minimization method which is more specific to this task, the algorithm appears to be able to improve the matching results of the standard method.

Radiosurgery is a radiation treatment modality in which a high radiation dose (few 1000 cGy) is given to a small volume (few cm$ sp3$) within the patient's brain during a single treatment. The main physical characteristics of radiosurgery are narrow circular radiation beams, stringent requirements on the numerical ($ pm$2%) and spatial ($ pm$1 mm) accuracy of dose delivery to the target and the need for sharp dose fall-offs outside the target volume. / Physical aspects of radiosurgery based on isocentric linear accelerators (linacs) are presented. The equipment and techniques used in the measurement of various radiosurgical beam parameters are discussed. Also discussed is the accuracy of radiation beam delivery to the target, the calculation and measurement of 3-dimensional isodose distributions obtained from circular beams, and the production of cylindrical dose distributions with rectangular beams. It is shown from the physics point-of-view that linac-based radiosurgery is a viable alternative to radiosurgery with the commercially available Gamma unit.

Recently, an important role has been attributed to endothelin-1 (ET-1), a potent vasoconstrictor and a mitogenic factor. The prostate and the vascular endothelium, including that of the penis, are known to produce ET-1. Furthermore, it has been shown that there are two receptor subtypes in the penis, ETa and ETb. Radiation treatment is known to cause an increase in ET-1 and may be a fundamental cause of radiation-associated impotence (RAI). / The aim of the present study was to evaluate the role of ET-1 in RAI. In the first part of our study, rats were divided into groups according to a different radiation dose. A ET-1 time course in tissue and serum was established. Markedly higher ET-1 levels were found in a high radiation dose compared with a lower dose and in the control group. / In the second part of the study, rats underwent evaluation of erectile function after radiation therapy. Subsequently, rats were given an antagonist of ETa (BQ-123) to assess whether the erectile response could be potentiated. Our results show that the use of this specific antagonist results in an improved erectile activity in a rat animal model. (Abstract shortened by UMI.)

A multimodality image fusion and localisation system for radiosurgery treatments of arteriovenous malformations (AVM) has been developed and validated. Within this system, three-dimensional magnetic resonance angiography (MRA) and two-dimensional digital subtraction angiography (DSA) vasculature information is combined with three-dimensional magnetic resonance (MR) and/or computed tomography (CT) anatomical information in order to benefit from the functionality of all modalities. MRA/MR/CT datasets are fused, and linked to the DSA images. The consistency of the linking procedure is verified by correlation of the DSA images with two-dimensional ray-traced projections of the MRA datasets. Organ contours are drawn on the MRA images, simultaneously visualised on their MR/CT counterparts, and projected onto the DSA images for visual feedback. This procedure allows users to incorporate both vascular and anatomical information in the three-dimensional target localisation and delineation process. Patient examples illustrating the utility of the system are presented.

The dynamic wedge is created by moving one of the primary beam limiting collimators in a continuous fashion to create a continuously decreasing field width while the radiation beam is on. Because of this collimator motion, different segments of the treatment field will be exposed to the primary beam for different intervals of time. This process of shrinking the field width while modulating the collimator jaw velocity and dose rate creates the desired wedge-shaped isodose gradient across the treatment field. The amount of dose that is delivered to the patient as the collimator moves across the treatment field is controlled by pre-specified computer selected look-up tables. / Before a dynamic wedge option can be implemented clinically, it must be thoroughly tested by measuring pertinent beam characteristics, thereby determining the reliability of this technology. Unlike beam measurements in static field radiotherapy, dynamic beam radiatiotherapy requires the use of an integrating dosimetry technique. In this thesis data was accumulated with the use of film dosimetry and direct integration ionization chambers. Using such systems the dosimetric properties of the dynamic wedge installed on a dual energy Clinac 2300 C/D linear accelerator were investigated. (Abstract shortened by UMI.)

Each of two detectors used in our Positron Emission Mammography (PEM) system consists of four 36mm x 36mm x 20mm bismuth germanate (BGO) detector blocks coupled to a crossed-wire anode photomultiplier tube (PMT). To achieve a high spatial resolution, the crystal blocks have been finely pixelated using a diamond saw. In each detector, 36 x 36 1.9mm x 1.9mm crystal elements are coupled directly to the PMT window and, on the opposite face of the blocks, 35 x 35 elements are offset by 0.9mm along both the x- and y-axes of the PMT. Techniques developed for the successful machining and surface-preparation of the detector blocks are described. Results indicating the detector block performance in terms of spatial and energy resolution are presented. / As part of a system calibration routine, a novel method for crystal element identification has been developed. This robust and reproducible algorithm succeeds in identifying 59 x 49 crystal elements on each detector face. The results are used to generate a Look-Up-Table (LUT) that is accessed during data acquisition for the effective correction of spatial distortion inherent in the detectors. Crystal identification also facilitates an improvement of the capability for accurate energy discrimination, since the detector gain and energy resolution are considered on an element-by-element basis by accessing an energy LUT. Employing a third LUT, which contains the relative efficiencies of individual crystal elements results in a significant improvement in detector uniformity.

X-ray mammography is currently the modality of choice for breast cancer screening. However, X-ray mammography cannot provide a positive diagnosis for cancer. A novel, dedicated breast imaging modality has been developed based on the principles of Positron Emission Tomography (PET). The Positron Emission Mammography (PEM) system is a sensitive, high resolution ($ sp sim2$ mm) breast scanner. PEM detects increased cell metabolism (indicating the presence of cancer) by imaging the distribution of tumour-specific metabolic radiotracers. The accurate co-registration of metabolic and X-ray breast images is important for localizing and characterizing suspicious lesions. Traditionally, registration between different imaging modalities has been difficult. PEM simplifies the image registration process by acquiring an X-ray image and a metabolic image consecutively, without moving the breast between scans. The PEM detectors are integrated into a conventional mammography unit and a co-registration tool has been developed. By providing metabolic information about a suspicious breast lesion, the number of invasive biopsy procedures (currently used to diagnose breast cancer) can be reduced.

Purpose. To evaluate the role of endovaginal sonography (EVS) and Doppler ultrasound in detecting endometrial carcinoma in women presenting with postmenopausal bleeding. / Materials & methods. We prospectively evaluated 421 women with EVS over a 5-year period. Of these 31 (7.4%) were diagnosed with endometrial carcinoma at histopathology. For each patient, biometric and morphologic parameters, as well as Doppler indices of the endometrium were obtained. / Results. Applying a combination of biometric and morphologic criteria, EVS diagnosed malignancy with a sensitivity of 77% (95% CI: 59%--90%) and a specificity of 84% (80%--87%). Using only biometric criteria (endometrial thickness >2mm indicating malignancy), EVS achieved a sensitivity of 100% (91%--100%) and a specificity of 24% (20%--29%), whereas the corresponding sensitivity and specificity for endometrial thickness >5mm was 74% (55%--88%) and 59% (54%--64%), respectively. The most predictive Doppler index was peak venous velocity (95% CI for odds ratio: 1.08--1.40). / Conclusion. Using a combination of biometric and morphologic sonographic criteria achieves the best accuracy in diagnosing patients with endometrial carcinoma, however at the cost of a decreased sensitivity.

No description available.

<p> In the spring of 2012, based on recommendations from the International Commission on Radiological Protection (ICRP), the Nuclear Regulatory Commission (NRC) proposed three amendments to reduce current radiation exposure limits for radiation workers. The NRC proposals have caused some concern within the radiopharmaceutical industry. The regulatory changes may affect the ability of radiopharmacy workers to remain on the job, thereby inflicting additional costs to radiopharmacies if they are required to replace workers who have reached their yearly exposure limits. </p><p> This research sought to determine whether or not the new regulatory proposals will in fact have a financial impact on the radiopharmaceutical industry. This research was a retrospective case study that analyzed four radiopharmaceutical production facilities and their employee radiation exposure reports. Results of the study suggest that the NRC's proposed amendments to reduce radiation levels will not have a great adverse effect, either financially or from an employee exposure standpoint, on the current radiopharmacy system. The research demonstrated that existing as low as reasonably achievable (ALARA) standards have resulted in radiopharmacy workers receiving exposures well below the current limits, and within the NRC proposed limits. Of 77 employees studied over a 10 year period, only seven employees (9 %) would have been removed from the production process for overexposure to any one of the NRC's proposed limits. However, this research reviewed small a subset of four radiopharmacies and did not examine other industries and professions utilizing ionizing radiation.</p>