Margin of planning target volume and dosimetric parameters of adaptive radiotherapy for esophageal cancer guided by cone beam CT images
Objective To explore the margin of planning target volume(MPTV)and dosimetric parameters of adaptive radiotherapy(ART)for esophageal cancer(EC)guided by cone beam CT(CBCT)images.Method A total of 30 pa-tients with EC were treated with ART.During the first week of treatment(days 1-5),they were scanned once a day,and then scanned twice a week thereafter.The CBCT image was fused and registered with the CT images of the initial radio-therapy plan(Plan0),the radiotherapy plan was adjusted according to the change of the target area to form an ART plan,which was compared with Plan0,and the overall positioning error and overall MPTV value of all patients in the X,Y and Z axes were analyzed.According to the body mass index(BMI),patients were divided into lean group(BMI<18.5 kg/m2)of 7 cases,normal group(18.5 kg/m2≤BMI<24.0 kg/m2)of 15 cases,and overweight group(BMI≥24.0 kg/m2)of 8 cases.The positioning errors and MPTV values on X,Y and Z axes of the three groups were analyzed.Under the condition of keeping the total irradiation times and dose unchanged,the ART was fused with Plan0,and finally a new fusion plan ART1 was generated.The dosimetric parameters of ART1 and Plan0 in normal tissues(heart,whole lung and spinal cord)of the three groups were compared.Result Among 30 patients with EC who underwent radiotherapy,the overall posi-tioning error in the X-axis direction was(0.16±0.12)cm,and the overall MPTV value was 0.484 cm.The overall position-ing error in the Y-axis direction was(0.15±0.14)cm,and the overall MPTV value was 0.474 cm.The overall positioning er-ror in the Z-axis direction was(0.28±0.23)cm,and the overall MPTV value was 0.861 cm.In the X-axis direction,the posi-tioning error and MPTV value of lean group were higher than those of normal group and overweight group,and the differ-ences were statistically significant(P<0.05).In the Y-axis direction,the positioning error and MPTV value of overweight pa-tients were higher than those of lean group and normal group,and the differences were statistically significant(P<0.05).In the Z-axis direction,the positioning error and MPTV value of lean group were higher than those of normal group and overweight group,and the differences were statistically significant(P<0.05).The exposure dose of ART1 in heart mean dose(Dmean),whole lung Dmean,and spinal cord maximum dose(Dmax)of three groups were significantly lower than those of Plan0,and the differences were statistically significant(P<0.01).Conclusion The application of ART technology guided by CBCT images in EC patients can significantly improve the accuracy and safety of radiotherapy.Real-time monitoring and dynamic adjustment of radiotherapy plan can significantly reduce positioning errors,optimize MPTV,and improve dosi-metric parameters.
esophageal cancercone beam CTadaptive radiotherapymargin of planning target volumedosimetric parameter
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