子宫颈癌俯卧位调强放射治疗摆位误差分析

Errors analysis of prone position in intensity modulated radiation therapy of cervical cancer

目的研究子宫颈癌俯卧位调强放射治疗的摆位误差大小，为子宫颈癌调强放疗计划设计临床靶区体积（CTV）外放计划靶区体积（PTV）时提供参考数据。方法选取行俯卧位调强放射治疗的子宫颈癌患者6例，所有病例治疗时身下垫有孔泡沫板，热塑成形固定膜固定。连续5d治疗时用电子射野影像装置（EPID）拍射正侧位验证片各1张，共60张验证片，通过配准数字化重建图像（DRR）和EPID拍摄的验证片的骨性解剖结构，计算平移和旋转误差。结果平移误差：左右方向为（3．1±1．8）mm、头脚方向为（3．9±3．3）mm、腹背方向为（4．2±2．6）mm；旋转误差冠状面为（0．8±0．9）°、矢状面为（1．2±1）°。结论对于子宫颈癌俯卧位调强放射治疗，CTV到PTV的外放应为左右7．1mm、腹背10．8mm、头脚10.4mm，在患者身体上做摆位的标记线有助于减少摆位误差。

Objective To study the spatial disuibution of set-up errors for cervical cancer with intensity modulated radiation therapy （IMRT） and to provide referential safety margin out of clinical tumor volume （CTV） during treatment plan design. Methods Six patients with cervical cancer were treated with IMRT in prone position,belly board and thermoplastic cast was used for immobilization. Measurement were made on a daily basis setup under five consecutive treatments with electron portal images device （EPtD）. Portal films from two projection （one anter-posterior and one opposite lateral）were taken. Sixty portal films were analyzed. The translational and rotational deviations were analyzed by registering and comparing the bony structures of EPID and digitally reconstructed radiographs （DRR）. Results The translational deviations were （3.1±1.8） mm, （3.9±3.3） ram, （4.2±2.6） mm in medi-lateral, cranio-caudal and anterior-posterior directions, the rotational deviations were in coronal plane （0.8±0.9）°and sagittal plane （1.2±1）°. Conclusion For the patients with cervical cancer undergoing IMRT, the margins between the CTV and FFV should be 7.1 mm in lateral direction, 10.4 mm in cranio-caudal and 10.8 mm in anterior-posterior directions. The sign on patients body can help to reduce the setup errors.