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Development and Validation of Precision in Small Animal Radiotherapy Dose Monitoring.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Development and Validation of Precision in Small Animal Radiotherapy Dose Monitoring./
作者:	Moore, Bria.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	111 p.
附註:	Source: Dissertations Abstracts International, Volume: 79-11, Section: B.
Contained By:	Dissertations Abstracts International79-11B.
標題:	Medical imaging. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10750590
ISBN:	9780355906073

Development and Validation of Precision in Small Animal Radiotherapy Dose Monitoring.
Moore, Bria.

Development and Validation of Precision in Small Animal Radiotherapy Dose Monitoring. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 111 p.

Source: Dissertations Abstracts International, Volume: 79-11, Section: B.

Thesis (Ph.D.)--Duke University, 2018.

This item must not be sold to any third party vendors.

Commercial x-ray irradiator units for small animal irradiation in preliminary cancer studies have become common in radiobiology research. As institutions and researchers acquire new equipment that is simpler to use, x-ray units are typically operated by users without supervision and physics support following initial set-up and training by manufacturers. However, experiments can have widely varying methods of set-up, calibration, and dosimetry. This has led to a documented lack of reproducibility in a variety of small animal studies. A primary contributing factor in this is the lack of standardization of dose delivery in small animals. It has been noted that in some cases the extreme steepness in radiobiology response curves can lead to a change in biological response from 5% to 90% levels with a variance in dose of 10%. Large scale studies that compare dose deliveries at several sites aim to describe a clear picture of the role of inaccurate dosimetry in the documented lack of reproducibility in preclinical studies. Small animal dosimetry is typically simplified into a single look-up table tabulated by device manufacturers or institutional physics groups. Thermoluminescent dosimeters (TLDs), specifically TLD-100 LiF chips, are generally accepted as the gold standard in kV x-ray dosimetry for small animal studies and these types of large scale projects. However, it is equally well known that these dosimeters require specific calibrations to convert light output to dose. Many comparison studies use half value layer (HVL) measurements to match TLD calibration curves to dose measurements. The dissertation will determine the appropriateness of the use of HVL as a normalizing factor for polychromatic x-ray beams. In addition to current dosimeter technology, our laboratory developed a novel dosimeter (Nano-FOD) that uses the combination of an organic scintillator pellet and a fiber optic technology to measure dose in real time. The scintillator pellet is composed of Europium-doped yttrium oxide which was demonstrated to have improved stimulated light production in nano-particle form vs. its bulk form, so the material was adapted for our application. To expand to new applications, such as organ-specific in vivo dosimetry for small animals, several physics characteristics have been investigated to inform us of the detector's expected behavior. Since TLDs are known to have slight differences in response based on batch and manufacturer date, three TLD batches from our institution that had been routinely used in kV x-ray applications were acquired. Batches were purchased between 2003 and 2011. Each batch was exposed at 5 different kVp values: 135, 150, 200, 250 and 320. At each kVp, the HVLs with matching filtration (2.5 mm Al + 0.1 mm Cu) as well as the necessary filtration to match the HVL at varying kVp values within ±5% was measured. The TLDs were exposed to these beams with matching beam filtrations as well as HVL-matched beams and measured calibration curves in each beam. A linear least-square fit was applied to each calibration curve and all R2 values were greater than 0.97. There was no correlation found between HVL and calibration slope in any of the three batches. With this information, it was determined that calibration curves from HVL matching in broad spectrum beams, such as those used in small animal irradiators, can lead to dose discrepancy of up to 300% at a true dose of 200 cGy. There was less variation between doses at lower energies, such as 135 and 150 kVp. In higher energy beams, there is a larger contribution of photons at characteristic energies. To minimize dose errors, the results of this study lead us to conclude that it is necessary to match both HVL and kVp to achieve an accurate dose calibration curve for TLD-100 chips. Our institution dosimetry protocol calls for both HVL and kVp matching inherently since calibration and exposure are usually taken in identical beams. To confirm the accuracy of our current methodologies, our x-ray irradiator and filters were recreated in the FLUKA advanced interface (flair). By modeling one of our small animal plexiglass phantoms, dose deposited in TLD dosimeters placed centrally in the phantom was calculated. These doses were compared to measured dose from TLDs and the nano-FOD. Doses agreed to within 1% between Monte Carlo and nano-FOD. The nano-FOD has current applications in high dose rate (HDR) brachytherapy, micro beam radiation therapy and x-ray dosimetry. Previous studies determined the angular dependence, lifetime radiation effects and linearity of the dosimetry. In this dissertation, data was compiled on temperature dependence and the detector energy response in orthovoltage and megavolt (MV) x-rays. (Abstract shortened by ProQuest.).

ISBN: 9780355906073Subjects--Topical Terms:

3172799
Medical imaging.

Development and Validation of Precision in Small Animal Radiotherapy Dose Monitoring.
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