固定束质子治疗病人摆位系统的精确性评估:等中心旋转运动

目的 评估固定束质子治疗的病人摆位系统等中心旋转运动的精确性。方法 将2 mm直径金属小球固定于床面之上并校准到房间等中心(ISO)。依次选择11个角度分别对治疗床进行等中心旋转,到达设定位置后使用数字影像摆位系统(DIPS)分别测算出小球与房间等中心的位移偏差。在不同时间共重复进行了四次测量,统计分析四组测量结果。结果 所有数据中,治疗床在-110°时发生位移最大,X、Y、Z轴方向分别是(0.29±0.05)mm、(0.21±0.04)mm和(-0.21±0.04)mm,小球与ISO总位移偏差(0.41±0.07)mm(1SD)。治疗床在30°时发生位移最小(0°除外),X、Y、Z轴方向分别是(-0.03±0.05)mm、(0.05 ±0.05)mm和(0.00±0.00)mm,小球与ISO总位移偏差(0.05±0.06)mm。结论 等中心旋转是实现固定束质子等中心多角度照射的关键运动模式。它是一种复杂的组合运动,包括治疗床床面的角度旋转运动和治疗床底座的水平轴向运动。由于质子治疗对靶灶精确定位的严格要求,这种组合运动的精度在质子治疗摆位中就显得格外重要。测量结果数据均小于0.5 mm。完全满足质子治疗PPS摆位精度的要求。

The Accuracy Assessment of PPS in Fixed Beam Proton Therapy: Isocentric Rotation Movement

Objective To assess the accuracy of isocentric rotation movement of Patient Positioning System (PPS) in fixed beam proton therapy.Methods A 2mm-diameter radioopaque sphere was positioned above the couch and was aligned to room isocenter (ISO).11 PPS angles were selected to make isocentric rotation test respectively.The displacement of the sphere to ISO were measured and calculated by Digital Image Positioning System (DIPS) respectively when PPS reached each designed position.Totally four group measurements were repeated at different time.all data were collected and statistical analysis were performed.Results The maximum shifts are (0.29±0.05) mm,(0.21±0.04) mm and (-0.21±0.04) mm on X,Y,Z axes at -110° PPS position,the absolute displacement of the sphere to ISO is (0.41±0.07) mm (1SD).The minimum shifts are (-0.03±0.05) mm,(0.05±0.05) mm and (0.00±0.00) mm on three principle axes at 30° PPS position,the absolute displacement of the sphere to ISO is (0.05 ±0.06) mm.Conclusion The isocentric rotation movement is the linchpin to realize multi-angle isocentric irradiation in fixed beam proton therapy.It is a complicated combined movement including PPS rotation and PPS translations.Since the high demand in the of precision of patient positioning,the accuracy of this combined movement played important role in proton therapy.In our tests,all shifts are less than 0.5 mm,can reach the requirement of positioning accuracy in proton therapy.