Biblioteca Digital

Optical-CT has been shown to be a potentially useful imaging tool for for the two very different spheres of biologists and radiation therapy physicists, but it has yet to live up to that potential. In radiation therapy, researchers have used optical-CT for the readout of 3D dosimeters, but it is yet to be a clinically relevant tool as the technology is too slow to be considered practical. Biologists have used the technique for structural imaging, but have struggled with emission tomography as the reality of photon attenuation for both excitation and emission have made the images quantitatively irrelevant.

Dosimetry. The DLOS (Duke Large field of view Optical-CT Scanner) was designed and constructed to make 3D dosimetry utilizing optical-CT a fast and practical tool while maintaining the accuracy of readout of the previous, slower readout technologies. Upon construction/optimization/implementation of several components including a diffuser, band pass filter, registration mount & fluid filtration system the dosimetry system provides high quality data comparable to or exceeding that of commercial products. In addition, a stray light correction algorithm was tested and implemented. The DLOS in combination with the 3D dosimeter it was designed for...

Purpose:

The feasibility of MRT has recently been demonstrated utilizing a new technology of Carbon-Nano-Tube (CNT) field emission x-ray sources. This approach can deliver very high dose (10's of Gy) in narrow stripes (sub-mm) of radiation, which enables the study of novel radiation treatment approaches. Here we investigate the application of high- resolution (50𝑢𝑚 isotropic) PRESAGE®/Optical-CT 3D dosimetry techniques to characterize the radiation delivered in this extremely dosimetrically challenging scenario.

Methods:

The CNT field emission x-ray source irradiator comprises of a linear cathode array and a novel collimating system. The device delivers small `stripe' beams of approximately X long and Y wide, at an energy of 160 kVp. To characterize the MRT beams, an ultra-high-resolution prototype 3D dosimetry system was constructed and optimized, consisting of two parts: a radiochromic 3D dosimetry material PRESAGE, and a high resolution small field-of-view optical-CT imaging system for dose-readout (DMicrOS - Duke Micro Optical-CT Scanner). Small PRESAGE cylindrical dosimeters (~2.2cm in height and ~2.5cm in diameter) were irradiated by CNT MRT delivering 3 stripes of radiation with a nominal entrance dose of 32 Gy (16Gy for the second batch). PRESGAE dosimeters (with same dimensions) were also irradiated with at 32 Gy entrance dose...

Quality assurance (QA) is a critical component of radiation oncology medical physics for both effective treatment and patient safety, particularly as innovations in technology allow movement toward advanced treatment techniques that require increasingly higher accuracy in delivery. Comprehensive 3D dosimetry with PRESAGE® 3D dosimeters read out via optical CT has the potential to detect errors that would be missed by current systems of measurement, and thereby improve the rigor of current QA techniques through providing high-resolution, full 3D verification for a wide range of clinical applications. The broad objective of this dissertation research is to advance and strengthen the standards of QA for radiation therapy, both by driving the development and optimization of PRESAGE® 3D dosimeters for specific clinical and research applications and by applying the technique of high resolution 3D dosimetry toward addressing clinical needs in the current practice of radiation therapy. The specific applications that this dissertation focuses on address several topical concerns: (1) increasing the quality, consistency, and rigor of radiation therapy delivery through comprehensive 3D verification in remote credentialing evaluations, (2) investigating a reusable 3D dosimeter that could potentially facilitate wider implementation of 3D dosimetry through improving cost-effectiveness...

Purpose: To demonstrate specific methods of small animal dosimetry and quality assurance through (1) machine-specific quality assurance and (2) target-specific quality assurance (QA) protocols for different types of biological irradiators: (a) a large-field orthovoltage irradiator, (b) a small-field orthovoltage irradiator, and (c) a 137Cs irradiator. Additionally, (3) a dosimetric characterization of a novel nano-scale phosphor detector for small animal dosimetry is performed.

Materials and Methods: (1) Machine-specific QA: (a) Large-field irradiator: Dose measurements were performed with an ion chamber and include: beam profile measurements at 50 cm SSD, linearity of output, in-air output for various irradiation settings, and light and radiation field coincidence measurement. A kVp meter was used to measure kVp and HVL for different irradiation settings. (b) Small-field irradiator: Dose measurements were completed using an ion chamber and MOSFET dosimeters. For the diagnostic mode measurements, the ion chamber was placed on the irradiation table and various diagnostic protocols were measured including table attenuation. MOSFETs were used to measure the backscatter factors (BSF) for various collimator sizes under therapy mode.

(2) Target-specific QA: (a) Large-field irradiator: A tissue-equivalent mouse phantom (2 cm diameter...