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實體與增強動態型楔形濾片對射束百分深度劑量調變之測量與研究

A Study on the PDD Modification of Physical and Enhanced Dynamic Wedges

摘要


Purpose: The percentage depth dose of physical and enhanced dynamic wedge fields of Varian CL-2100 CD linear accelerators were measured. According to the variation of the PDD values, PDD modification effect of both type wedges will be observed and discussed. Materials and Methods: The PDD curves of open and physical wedged fields were measured with Nucletron 3D water phantom equipped with 0.12 cc Scanditronix RK ionization chamber. The PDD values of enhanced dynamic wedged fields were measured with Keithley 35040 dosimeter connected to Wellhofer Focus PPC-35 parallel plate ionization chamber. The beam energies are 6 and 10 MV. The measured field sizes are 5×5, 10×10, 15×15, 20×20cm^2. The wedge angles are 15°, 30°, 45° and 60°. The depths are surface, the dm, 5, 10, 15, 20cm. Each value were normalized to it's own D(subscript max) to compare the PDD variation. Results: The beam hardening effect of physical wedged field were inverse to beam energy and field size. But increase when the depth and wedge angle increased. The maximum PDD increment (2.23%) is located at 6 MV, 5×5cm^2 field size, 60° wedge angle and depth equal to 20cm. The PDD modification effect of enhanced dynamic wedged field was inverse with beam energy, but increased when the field size, the depth and the wedge angle increased. The maximum PDD increment (1.14%) is located at 6MV, 20×20cm^2 field size, 60° wedge angle and depth equal to 20cm. Conclusions: The PDD modification effect of enhanced dynamic wedged field are really exist. The effect from the physical wedge is due to the filtering effect of the wedge material. The effect from the enhanced dynamic wedge is due to the dose-gradient effect.

並列摘要


Purpose: The percentage depth dose of physical and enhanced dynamic wedge fields of Varian CL-2100 CD linear accelerators were measured. According to the variation of the PDD values, PDD modification effect of both type wedges will be observed and discussed. Materials and Methods: The PDD curves of open and physical wedged fields were measured with Nucletron 3D water phantom equipped with 0.12 cc Scanditronix RK ionization chamber. The PDD values of enhanced dynamic wedged fields were measured with Keithley 35040 dosimeter connected to Wellhofer Focus PPC-35 parallel plate ionization chamber. The beam energies are 6 and 10 MV. The measured field sizes are 5×5, 10×10, 15×15, 20×20cm^2. The wedge angles are 15°, 30°, 45° and 60°. The depths are surface, the dm, 5, 10, 15, 20cm. Each value were normalized to it's own D(subscript max) to compare the PDD variation. Results: The beam hardening effect of physical wedged field were inverse to beam energy and field size. But increase when the depth and wedge angle increased. The maximum PDD increment (2.23%) is located at 6 MV, 5×5cm^2 field size, 60° wedge angle and depth equal to 20cm. The PDD modification effect of enhanced dynamic wedged field was inverse with beam energy, but increased when the field size, the depth and the wedge angle increased. The maximum PDD increment (1.14%) is located at 6MV, 20×20cm^2 field size, 60° wedge angle and depth equal to 20cm. Conclusions: The PDD modification effect of enhanced dynamic wedged field are really exist. The effect from the physical wedge is due to the filtering effect of the wedge material. The effect from the enhanced dynamic wedge is due to the dose-gradient effect.

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