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Setup Error Effects of Different Cycles During Treatment Process of Esophageal Cancer Radiotherapy

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Z Chi

K Shang, Z Chi*, J Wang, The Fourth Hospital of HeBei Medical University, Shijiazhuang, Hebei Province

SU-E-J-210 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The purpose of this study is to measure setup errors before treatment delivery and observe the change of setup errors throughout the entire course of radiotherapy.

Methods:There were 23 esophageal cancer patients were treated by Elekta linear accelerator, a total of 405 CBCT scans were analysed. The systematic and random errors were calculated in the X, Y, Z axis. The date of each group was analysed by SNK statistical method.

Results:All data can be divided into 6 groups. It is respectively the first to fifth week and general setup errors. The systematic and random errors (cm) in the X axis were 0.33, 0.32, 0.34, 0.37, 0.45,0.35 and 0.28, 0.28, 0.31, 0.32, 0.34, 0.31. The systematic and random errors (cm) in the Y axis were 0.61, 0.62,0.65, 0.66, 0.61, 0.63 and 0.5, 0.5, 0.53, 0.54,0.46, 0.53. The systematic and random errors (cm) in the Z axis were 0.26, 0.26, 0.29, 0.29, 0.37,0.29 and 0.19, 0.2, 0.21, 0.21, 0.24, 0.21. It has found that the systematic error gradually increased with the increase of treatment time in the X, Z axis, setup errors have no obvious change in the Y axis. No significant correlations were found between each group in the Y axis, P value > 0.05. The fifth week and other groups was found to be significant in the X and Z axis, P values < 0.05, no significant correlations were found between the rest groups, P value > 0.05.

Conclusion:The first week or previous setup errors can guide subsequent treatment, but in the end of treatment (after at most 20 times) the treatment plan should be redesigned. Because each treatment situation is different, if allows, the CBCT should be used for each treatment.

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