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Development of a Graphite Probe Calorimeter for Absolute Clinical Dosimetry

其他書名	Numerical Design Optimization, Prototyping and Experimental Proof-of-concept
出版	McGill University Libraries, 2012
URL	http://books.google.com.hk/books?id=uh7MoAEACAAJ&hl=&source=gbs_api

註釋"In this work, the feasibility of absolute dose to water measurements using a small scale graphite probe calorimeter (GPC) in a clinical environment is established. A numerical design optimization study was conducted by simulating the heat transfer in the GPC resulting from irradiation using a finite element method software package. The choice of device shape, dimensions and materials was made to minimize the heat loss in the sensitive volume of the GPC. The resulting design, which incorporates a novel aerogel-based thermal insulator, was built in-house. Absorbed dose to water measurements were made under standard conditions in a 6 MV 1000 MU/min photon beam and subsequently compared against TG-51 derived values. The average measured dose to water was 95.7 ± 1.4 cGy/100 MU, as compared to an expected value of 96.6 cGy/100 MU. The Monte Carlo-calculated graphite to water dose conversion factor was 1.099, while the derived heat loss correction factors varied between 1.005 and 1.013. The most significant sources of uncertainty were the repeatability (type A, 1.4%) and thermistor calibration (type B, 2.1%). The contribution of these factors to the overall uncertainty is expected to decrease significantly upon the implementation of active thermal stabilization provided by a temperature controller and direct electrical calibration, respectively. This proof of concept demonstrates the feasibility of using the GPC as a practical clinical absolute photon dosimeter and lays the foundation for a miniaturized version suitable for small and composite field dosimetry."--