加速器MVCBCT扫描图像在自适应放疗中应用的可行性研究

Feasibility study on the application of accelerator MV CBCT images in adaptive radiation therapy

目的探讨加速器成像射束影像系统（IBL）的全扇形柬和大射野（EFOV）两种模式扫描得到的兆伏级锥形束断层（MVCBCT）图像可否用于剂量计算。方法利用大孔径CT和在IBL的全扇形束和EFOV模式下对CIRS062M型电子密度模体进行扫描，在Pinnacle计划系统中分别建立电子密度曲线。用CT和加速器MV级CBCT模式扫描头颈、胸、腹盆腔部仿真模体，利用CT图像制作调强计划，并将计划移植于MVCBCT的图像中，利用相应的电子密度曲线计算剂量，比较靶区及危及器官剂量分布。结果MVCBCT图像中剂量分布比参考计划剂量偏低，并且在头颈、胸、腹盆腔模体中偏差依次增大。与参考计划相比，头颈部靶区剂量和危及器官剂量分布一致，偏差均在3％以内。胸部和腹盆腔靶区和危及器官的剂量分布均有大幅度的降低，偏差分别达到5％和10％，超出了临床接受范围。结论在加速器IBL中全扇形束模式条件下，头颈部患者扫描得到的MVCBCT图像可在自适应放疗中用于剂量计算，胸、腹盆腔部位在EFOV模式下仅可用于图像引导，不能用于剂量计算。

Objective To investigate whether the accelerator image beam line （IBL） full scan and extend field of view（EFOV） scan mode megavoltage cone beam CT（MV CBCT） images can be used for dose calculation in adaptive radiotherapy. Methods The large aperture CT and MV CBCT were used to scan the CIRS 062M electron density modules, the CT value was established to electron density curves in the Pinnacle treatment planning system. Also, CT and MV CBCT were used to scan the head and neck, chest, abdomen and pelvis phantom. The intensity modulated radiotherapy（IMRT） plans were made with CT images and transplanted to MV CBCT images. The dose of targets and organs with their electron density curves was calculated, and two type IMRT plans with different CT images were compared. Results The dose distribution of head and neck phantom was acceptable, compared with the reference plan, the difference was within 3% . The dose distribution of chest and pelvis was significantly reduced from reference plans, and the difference was 5% and 10% separately. This difference was beyond the scope of clinical acceptance. Conclusions MV CBCT images of accelerator IBL full scan mode in patients with head and neck site scan could be used for dose calculation in adaptive radiotherapy, chest and pelvic sites in EFOV mode scanning MV CBCT images could only be used for image guidance.