Full text
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| Author(s): |
Juliana Cristina Martins
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física (IF/SBI) |
| Defense date: | 2015-12-07 |
| Examining board members: |
Paulo Roberto Costa;
Marcelo Baptista de Freitas;
Vito Roberto Vanin
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| Advisor: | Paulo Roberto Costa |
| Abstract | |
Since its development in 1970s the computer tomography (CT) technique have gone through major technological advances, becoming an important diagnostic tool in medicine. Consequently the role of CT in diagnostic imaging expanded rapidly, mainly due to improvements in image quality and speed of acquisition. The radiation dose imparted in patients undergoing CT scans has gained attention, leading the radiology community (radiologists, medical physicists and manufacturers) to work together towards dose estimation and optimization. New methodologies for patients dosimetry have been proposed in the past decades, based specially on Monte Carlo calculations or experimental measurements with phantoms and dosimeters. In vivo methodologies are also under investigation. Current dose optimization strategies include mainly tube current reduction and/or tube current modulation. The present work proposes a methodology to experimentally estimate lung absorbed doses due to clinical CT protocols using an adult anthropomorphic phantom and Lithium Fluorite (LiF) thermoluminescent dosimeters (TLD). Seven clinical protocols were selected for phantom irradiation, based on their relevance regarding dose optimization and frequency in two major hospitals routine: the Institute of Radiology from the Medical Faculty from the University of São Paulo (Instituto de Radiologia do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo InRad) and the Cancer Institute of the State of São Paulo Octávio Frias de Oliveira (Instituto do Câncer do Estado de São Paulo Octávio Frias de Oliveira ICESP). Fours thorax protocols for dose optimization were analyzed: Auto mA, Auto + Smart mA, Low Dose (LD) and Ultra Low Dose (ULD) thorax. The first two aforementioned protocols seek dose reduction by tube current modulation, while the last two propose a decrease on the constant tube current value. Values of 72.9(8) % and 91(1) % of lung dose reduction were achieved with LD and ULD protocols, respectively. Auto mA and Auto + Smart mA provided 16.8(1.3) % and 35.0(1.2) % of lung dose reduction, respectively. The results from all analyzed protocols are compatible with similar studies published in literature, demonstrating the efficiency of the methodology to lung absorbed dose estimation. Its applicability could be extended to different organs, different clinical CT protocols and pediatric phantoms. Moreover, comparison of lung absorbed doses and Size Specific Dose Estimates (SSDE) for the studied protocols exhibited a tendency of linear dependency. Results from similar studies demonstrate a similar behavior between rectal doses and SSDE, suggesting that organ absorbed doses and SSDE values may be linearly dependent, with organ-specific linear coefficients. Further investigation in organ doses is necessary to evaluate this assumption. (AU) | |
| FAPESP's process: | 13/09596-3 - Dose estimates in adult and pediatric computed tomography procedures |
| Grantee: | Juliana Cristina Martins |
| Support Opportunities: | Scholarships in Brazil - Master |