Context:The errors made during repetitive patient placements affect significantly the accuracy of treatment and the results of radiotherapy.Objectives:To determine the total,systematic and random error in order to est...Context:The errors made during repetitive patient placements affect significantly the accuracy of treatment and the results of radiotherapy.Objectives:To determine the total,systematic and random error in order to estimate the margin between the Clinical Target Volume(CTV)and the Planning Target Volume(PTV)in the pelvic region.Materials and methods:Set up errors was estimated by superimposing a digitally reconstructed radiograph(DRR)as a reference image with an electronic portal image device(EPID).The total errors in the Medio-Lateral(ML),Cranio-Caudal(CC)and Antero-Posterior(AP)directions were compared by t-test.For systematic and random errors,the ratio of variance(F statistic)was used.Margins were calculated using Van Herk formalis.Results:208 images(80 DRRs and 128 EPIDs)were assessed.The systematic error ranged from 1.93 to 2.01 mm,1.26 to 1.39 mm,and 1.20 to 2.94 mm in the x,y and z-axis,respectively.The random error ranged from 2.33 to 2.90 mm,1.25 to 1.66 mm,and 1.04 to 1.28 mm.The PTV margin according to the Van Herk equation in the x,y and z directions was estimated to be 7.11,4.64 and 3.90 mm for the cervix uteri and a 6.47,4.03,and 3.70 mm for the rectum.Conclusion:The use of weekly EPID/DRR allows estimating the setup of the planning target volume(PTV)expansion according to our configuration.In this study,the evaluated set up margin was approximately 8 mm in the X-axis,5 mm in Y and Z axis for pelvic conformal radiotherapy.展开更多
基金We thank the staff at Regional Center of Oncology of Agadir for their help during data collections.No authors received funding for this research study.
文摘Context:The errors made during repetitive patient placements affect significantly the accuracy of treatment and the results of radiotherapy.Objectives:To determine the total,systematic and random error in order to estimate the margin between the Clinical Target Volume(CTV)and the Planning Target Volume(PTV)in the pelvic region.Materials and methods:Set up errors was estimated by superimposing a digitally reconstructed radiograph(DRR)as a reference image with an electronic portal image device(EPID).The total errors in the Medio-Lateral(ML),Cranio-Caudal(CC)and Antero-Posterior(AP)directions were compared by t-test.For systematic and random errors,the ratio of variance(F statistic)was used.Margins were calculated using Van Herk formalis.Results:208 images(80 DRRs and 128 EPIDs)were assessed.The systematic error ranged from 1.93 to 2.01 mm,1.26 to 1.39 mm,and 1.20 to 2.94 mm in the x,y and z-axis,respectively.The random error ranged from 2.33 to 2.90 mm,1.25 to 1.66 mm,and 1.04 to 1.28 mm.The PTV margin according to the Van Herk equation in the x,y and z directions was estimated to be 7.11,4.64 and 3.90 mm for the cervix uteri and a 6.47,4.03,and 3.70 mm for the rectum.Conclusion:The use of weekly EPID/DRR allows estimating the setup of the planning target volume(PTV)expansion according to our configuration.In this study,the evaluated set up margin was approximately 8 mm in the X-axis,5 mm in Y and Z axis for pelvic conformal radiotherapy.
