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目的:应用电子射野影像系统测量自由呼吸状态(FB)和主动呼吸控制状态(ABC)下的相对位移,并对比其差别。方法:选择29例接受保留乳房术后调强放疗的乳腺癌患者,16例在FB下13例在ABC下接受放疗。患者在每次放疗前拍电子射野影像片(EPI),ABC的8例在每次放疗前拍2次。依据胸壁和乳腺表面轮廓将EPI和数字重建图像(DRR)进行配准,计算出每次配准时垂直和水平方向的差异。结果:FB组水平和垂直方向的平均位移分别为1.93和0.99mm,ABC组分别为1.97和1.14mm。位移>5mm的<4%。ABC组之间在水平和垂直方向的位移差异无统计学意义,P值分别为0.778和0.142。其中8例每次放疗前拍2次EPI的ABC患者,在水平和垂直方向差异无统计学意义,P值分别为0.220和0.862。结论:尽管从理论上ABC可减少呼吸运动,但在减少由摆位误差和呼吸运动造成的混合位移方面并无优势。乳腺癌放疗时从临床靶区到计划靶区外放5mm的边界是合理的。
OBJECTIVE: To measure the relative displacement under Free Respiratory State (FB) and Active Respiratory State (ABC) using electronic field imaging system and to compare the differences. METHODS: Twenty-nine breast cancer patients underwent IMRT with retained breast surgery and 13 of 13 under the FB were treated with radiotherapy. Patients underwent radiofrequency imaging (EPI) before each radiotherapy, and ABC in eight patients before radiotherapy twice. The EPI and the Digital Reconstructed Image (DRR) were registered according to the chest wall and breast surface contours to calculate the vertical and horizontal differences for each registration. Results: The mean horizontal and vertical displacements of FB group were 1.93 and 0.99 mm respectively, while those of ABC group were 1.97 and 1.14 mm respectively. <4% of displacement> 5mm. There was no significant difference in horizontal and vertical displacement between the ABC groups, with P values of 0.778 and 0.142, respectively. Eight patients with EPI twice before each radiotherapy had no significant difference in horizontal and vertical directions, P values were 0.220 and 0.862, respectively. CONCLUSIONS: Although ABC can theoretically reduce respiratory motion, it has no advantage in reducing the combined displacement caused by setting errors and respiratory motion. Breast cancer radiotherapy from the clinical target to the planning target outside the 5mm boundary is reasonable.