RESUMEN
Objective To investigate the movement and its influencing factors of the space-occup ying pancreatic lesions and provide a reference for the safe margin between CTV and PTV in accurate radio therapy.Methods Gold fiducials were implanted into the lesions of 16 pancreatic carcinoma patients by percutaneous punctures under B-uhrasonographic guidance.The movements of these markers were measured under the X-ray simulator system in the x,y and z axial directions,respectively.The relevant influencing fac tors were analyzed.Results The motion amplitudes of pancreatic lesions were 0.1-0.3 (mean 0.16 ± 0.06) cm,0.1-0.4 (mean 0.25 ±0.12) em and 0.5-1.6 (mean 0.88±0.24) cm in the x,y and z axi al directions,respectively.The movements were not associated with the height,weight,age,tumor location or tumor size.Conclusions The motion of the space-occupying pancreatic lesions is mainly influenced by the respiration,especially with the maximal amplitude in the z axial direction.Therefore,the motion in the z axial direction should be given more consideration when determining the PTV margin.