%A LI Xin-ping, ZENG Xian-wen, XU Wen-ling, et al %T The Accuracy Assessment of PPS in Fixed Beam Proton Therapy: Isocentric Rotation Movement %0 Journal Article %D 2005 %J Chinese Journal of Radiological Health %R 10.13491/j.cnki.issn.1004-714x.2005.03.005 %P 170-172 %V 14 %N 3 %U {http://www.zgfsws.com/CN/abstract/article_3832.shtml} %8 2005-09-28 %X 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.