(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To Investigate the effect of a new carbon fiber couch for the new linear accelerator from Shanghai United Imaging Healthcare Co., Ltd on the radiotherapy dose.
Methods: Percentage depth dose(PDD) were measured by the square water phantom and EBT film, as the field sizes were from 5×5cm2 to 25×25cm2. The attenuation measurements were also performed by the square water phantom with the gantry angles from 180°~110° for three different positions(offset=0, offset=+10cm, offset=-10cm). Scanning and being contoured the carbon fiber couch and phantom at three positions, the dose deviation between measurements and calculations were calculated, and attenuation in TPS for different gantry angles were also calculated.
Results: The surface dose and the buildup region were increased with the field sizes. The surface dose range from 23.40% to 41.15% with the field size from 5×5cm2 to 25×25cm2 with the angle 0° , while from 73.74% to 93.56% for angle 180°. The attenuation factors for 6 MV were 0.044-0.085 at offset=0cm, 0.044-0.127 at offset=+10cm, 0.043-0.093 at offset=-10cm. Without the couch model in TPS, the dose deviation for different gantry angle ranged from -0.129% to -0.397%, but ranged from -0.621% to -5.126% for three algorithms.
Conclusion: A carbon fiber couch significantly affect the surface dose. The attenuation of the new carbon fiber treatment couch of linear accelerator from Shanghai United Imaging Healthcare Co., Ltd varies at different positions with different angles of gantry. When the angle of gantry was 130°~110°, the dose attenuation is higher at the right side of treatment couch that at the middle and the left, and the maximum is at 110°. Those angles causing larger dose attenuations should be avoided in oblique field plan.
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