| Background and purpose:In recent years,with the continuous updating of equipment and development of technology,radiotherapy has entered an era of precise treatment.The precision of target volumn is continuously improved with various of new technologies used in the clinical application,therefore,how to reduce the error during the treatment has became a hot spot.Initially,the patient received radiotherapy without any immobilization devices.The patients lied on the treatment bad directly without any support for body,so that they were prone to movement and rotation during the treatment.With the continuous development of auxiliary equipment,a variety of immobilization devices are currently used to limit the movement of patients and reduce the setup error.Stereotactic body frame combined with vacuum suction pads and carbon fiber holder combined with shaped mats plus thermoformed film are two kinds of new immobilization systems,and they has just began to be used in the clinical treatment.There is no comparative study of setup error between the two different immobilization systems in the treatment at present.Image-guided radiotherapy technology applies a variety of advanced imaging equipment to monitor the changes of position of tumors and organs at risk before and during the treatment.Online or offline correction is used to reduce the linear and angular errors in three-dimensional directions,and also adjust the treatmen t conditions according to changes in the position of organs.Cone beam CT had a better ability to reduce the linear error and the angle error than the other imaging guided radiotherapy techniques,and it combined with six-dimensional bed that would correct error automatically to achieve the purpose of precision treatment.Therefore,we applied the kV cone beam CT to determine the linear errors and angular errors of two different immobilization systems in radiotherapy for thoracic and abdominal carcinoma.And we calculate the corresponding safety margins with system error and random error for reference in clinical application.Materials and Methods:A total of 28 patients with thoracic and abdominal carcinoma who treated in our department from June 2017 to January 2018 were divided into two groups.Fourteen patients were treated with stereotactic body frame combined with vacuum suction pads immobilization systems(group A),the mean age is(60.67±15.30)years old.Another 14 patients whose mean age is(58.22±14.50)years applied carbon fiber holder combined with shaped mats plus thermoformed film.All patients' karnofsky scores were more than 70 points.The kV cone beam CT was used for on-line verification and the data was collected.SPSS 18.0 computer statistical software was used to perform statistical analysis of all the data to compare the setup errors of two different immobilization systems,p<0.05 means that the difference was statistically significant between the two groups.Planning target volume corresponding safety margins were calculated with the error data.Results:A total of 206 kV cone beam CT images were collected from 28 patients.There was no significant difference between the two groups in sex,age and frequency of CBCT image verification(p>0.05).The linear errors in group A were(-0.41±3.64)mm in the longitudinal direction,(2.79±3.93)mm in the longitudinal direction and(-0.07±4.40)mm in the vertical direction,respectively;and the angular errors were(-0.00±0.80)°,(-0.02±0.24)° and(0.05±0.24)°,respectively;In the group B,the linear errors were(0.27±3.12)mm,(-2.21±6.03)mm and(0.39±2.82)mm,respectively;and the angular errors were(-0.03±0.86)°,(0.14±1.11)° and(1.39±1.82)°,respectively.The values of p between the two groups were 0.628,0.000,0.000,0.305,0.123,0.000,respectively.In the three directions,the release boundaries of planning target volume in group A were 5.08 mm,10.33 mm and 3.85 mm,respectively;these in group B were 3.80 mm,9.60 mm and 4.17 mm,respectively.Conclusions:Both of the two immobilization systems can fix the position of patient effectively.The linear error and angular error in the z axis in group A were significantly less than those in group B(p<0.05);The linear error in y axis in group B was significantly less than that in group A(p<0.05).There was no significant difference in the other directions(p>0.05).These two different immobilization systems could significantly reduce the setup error,so that they are worthy to be applied in clinics.The release boundaries of planning target volume can be adjusted based on the above data. |
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