| Summary: | 碩士 === 元培科學技術學院 === 影像醫學研究所 === 94 === Abstract
Medical linear accelerators generate two radiation beams including photon and electron beams. These beams could interact with target, collimators, flattening filter, air and even patient body. Several types of photonuclear reactions such as (γ,n)、(γ,2n)、(γ,pn) occurs to make the photon-neutron mixed fields. The purpose of this research is to measure the distributions of the lineal energy in these mixed fields which induced by different energies of photon and electron beams. Microdosimetry distinguishes the energy deposition events of high linear energy transfer radiations in microdosimetric view, and defines the probability function and probability density of lineal energy and specific energy in single event. A tissue equivalent proportional counter (TEPC) was chosen to measure the parameters of microdosimetry in this work. TEPC was filled with the propane based tissue equivalent gas to simulate a 2 µm size cell or tissue and the energy imparted irradiated with different energy of photons and electrons were measured. Am-241 calibrated source was placed on the wall surface of the TEPC to perform the energy calibration before the clinical measurement trial, therefore, relationship between imparted energy and channel of the spectra can be calculated. Microdosimetric spectra estimated from this work could estimate the frequency mean lineal energy, the dose mean lineal energy and relative biological effectiveness (RBE), these parameters are also the important references indexes for clinical radiotherapy.
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