锥形束CT联合六维床在子宫颈癌放疗中的应用及靶区外放边界的分析研究

目的:锥形束CT（CBCT）联合六维（6D）治疗床纠正子宫颈癌调强放疗摆位精度及靶区外放边界的研究。方法:随机选取2020年10月至2021年4月中山大学肿瘤防治中心36例子宫颈癌患者，年龄35～70岁；卡氏评分>80分。接受容积调强放射治疗（VMAT），每例患者每次治疗前进行CBCT扫描共714次，得到容积CT图像，...

Application of cone beam CT combined with six-dimensional bed in cervical cancer radiotherapy and analysis of boundary of target area

Objective　To study the accuracy of the placement of cervical cancer withintensity-modulated radiation therapy (IMRT) adjusted by cone beam CT (CBCT)and six-dimensional 6D treatment bed and the boundary of the target area. Methods　Thirty-six patients with cervical cancer whowere 35-70 years old treated at Sun Yat-sen University Cancer Center fromOctober 2020 to April 2021 were randomly selected. Their Karnofsky score wasover 80. After volumetric intensity modulated radiation therapy (VMAT), eachpatient underwent CBCT scans a total of 714 times before each treatment toobtain a volume CT image, which was then registered with the localization CTimage, and performed 6D registration again, and the 6D setup error value wasrecorded. The body mass index (BMI) of each patient was recorded. Theinfluences of BMI on the coronal plane Rtn, sagittal plane Pitch, transverseplane Roll, and other directions in the 6D registration was analyzed. Accordingto the Van Herk formula M_PTV=2.5∑+0.7σ, the corresponding extrapolation boundaryvalue (MPTV) in the translation direction was calculated. Independent sample t test and paired t test were performed on all the data. Results　The absolute values of the placement errors of 3D registration in theleft and right (LR), head-to-foot (SI), and ventral dorsal (AP) directions were(2.1±0.9), (3.2±1.2), and (2.3±1.2) mm, and those of 6D registration were(1.8±0.6), (3.2±1.0), and (2.2±0.8) mm. The paired t test was used for the original data, and there was no statisticaldifference in the SI direction (P>0.05),and were in the LR and AP directions (all P<0.05).Under the influence of BMI, there were statistical differences in the therotation and positioning errors in the directions of yaw angle (Rtn), pitchangle (Pitch), and roll angle (Roll) between the normal and obese patients (all P<0.05). The 6D registration wasreduced by 1.0, 2.0, and 1.6 mm in LR, SI, and AP as compared with the 3Dregistration by calculating the extrapolation boundary. Conclusions　For CBCT combined with 6D treatment table online correction, 6D imageregistration is better than 3D image registration. According to the formula M_PTV=2.5∑+0.7σ, the 6D extension boundary is smaller thanthe 3D extension boundary; in the clinical radiotherapy for cervical cancer,the use of 6D image registration combined with a six-dimensional bed has moreadvantages than a single three-dimensional bed, which can reduce the dose ofnormal tissues around the target area and improve the accuracy of tumorradiotherapy.