An Analysis Method of Dose Error Caused by the Couch Tilt of CT Simulation Machine

摘要

Purpose: If the horizontal plane is inconsistent between computer tomography (CT) couch and line accelerator (LA) couch, the position of the isocenter point in the radiotherapy treatment planning system (TPS) should deviate from that of it on the accelerator couch board. Then, the actual dose distribution was different from the radiotherapy plan we designed in TPS. This paper introduces a method to evaluate the dose deviation caused by the tilt of CT couch. Methods: We calculated the isocenter points of the position coordinates both in CT couch and LA couch, and compared the dose distribution when the twopositions of isocenter points were applied in radiotherapy plan independently in TPS. The dose distribution difference of a breast radiotherapyplan was analyzed as a demonstration with this method. Results: The distance between the two isocenter positions increased with angle of CT couch. The tilt of the couch had an impact on the dose distribution, especially in larynx's maximum dose parameter. Conclusion: This method could quantitatively analyze the dose distribution deviationcaused by the tilt of CT couch plate. The results can provide a valuable suggestion for clinical medical strategy.