The Research on Target Area External Radiation Boundary Based on Positioning Error of Tomotherapy
Objective To analyze the positioning error of tomotherapy with megavoltage computed tomography(MVCT)image guidance for patients with nasopharyngeal carcinoma,breast cancer,and cervical cancer,and calculate the corresponding target expansion boundary of nasopharyngeal carcinoma,breast cancer and cervical cancer patients,so as to provide a basis for the determination of clinical target volume to planned target volume(CTV-PTV).Methods With the random selection of 90 patients visited to the radiotherapy center of Guangdong Provincial Hospital of Traditional Chinese Medicine for spiral tomotherapy from October 2022 to September 2023,including 30 patients with nasopharyngeal cancer,30 patients with breast cancer,and 30 patients with cervical cancer,before treatment,MVCT was used to analyze the positioning error of all patients.MVCT images were collected 900,870,and 900 times for nasopharyngeal cancer,breast cancer,and cervical cancer patients,respectively.The positioning error was obtained by comparing with the planned CT.The average error(∑)and standard deviation(δ)in the left and right(x),head and foot(y),and front and back(z)directions of the tumors at different sites were calculated,and the boundary value of the target area expansion was determined.Results The positioning errors of nasopharyngeal carcinoma patients were+x(1.45±1.12),-x(1.50±1.56),+y(2.01±1.51),-y(1.65±1.25),+z(2.10±1.26),-z(1.25±1.13)mm.The positioning errors of breast cancer patients were+x(3.55±2.52),-x(3.56±3.13),+y(3.15±3.32),-y(3.12±3.02),+z(5.48±3.01),-z(3.32±2.46)mm.The positioning errors of cervical cancer patients were+x(3.02±2.35),-x(3.12±2.32),+y(3.11±2.56),-y(3.04±2.86),+z(5.02±2.89),-z(3.12±2.13)mm.The external radiation boundary of nasopharyngeal carcinoma patients in six directions was(2,2,3,3,3,3)mm,that of breast cancer patients in six directions was(3,3,7,7,8,5)mm,and that of cervical cancer patients in six directions was(3,3,7,7,7,4)mm.Conclusions In tomotherapy,the positioning error of nasopharyngeal carcinoma patients was smaller than that of tumor patients in other parts,and the positioning error of breast cancer patients was the largest.Through the positioning error,the external expansion boundary of the target area was determined to improve the quality of radiotherapy for patients.
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