| Summary: | 碩士 === 中國醫藥大學 === 臨床醫學研究所碩士班 === 101 === To ensure that dose output accuracy of radiotherapy system among all hospitals, many international organizations establish the postal dosimeters audit networks to verify whether dose output within the tolerance value. Currently, there are no standardization methods for dose measurement to verify whether the dose output of machine and treatment planning system are accurate among hospitals in Taiwan. So, the aim of our research is the establishment of dosimetric audit network in Taiwan, including phantom design, dose measurement, and stability test.
Our research verifies the beam parameters of radiotherapy machine, including dosimetric parameter, field size factor, field flatness and symmetry. In order to verify the dose output accuracy of treatment planning system, we also make the treatment planning and irradiating follow it. Our research used thermolumonescent dosimeters and radiochromic films as postal dosimeters, and produced the homogeneous postal phantoms and the inhomogeneous postal phantoms. And then we designed the dose modified formula that includes the important correction factors to calculate correct absorbed dose. This study measured all audit programs with ion chamber and assessed the measurements difference between postal dosimeters and ion chamber, and thus evaluated the stability of the postal audit system.
In the results, the maximum dose difference of the verification on dosimetric parameter, field size factor, field flatness and symmetry were 1.6%, 3.2% and 2.6% respectively. It shows that the self-designed methods of dose measurement are stable. And then the beam parameters calculation by the dose measurement, the values were consistent with hospital beam data. We could see the difference of inhomogeneous correction capability between each algorithm by measuring the dose output of treatment planning system with inhomogeneous postal phantoms. It shows the inhomogeneous postal phantoms have the function to identify correction capability of algorithms. So, the self-designed postal phantoms and dose measurement can be used to verify the dose output accuracy of radiotherapy system.
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