小细胞肺癌三种全脑预防性照射计划的剂量学比较

Comparison of dosimetry in radiotherapy for prophylactic cranial irradiation for prophylactic cranial irradiation in small cell lung cancer

目的 比较小细胞肺癌（SCLC）全脑预防性照射（PCI）3D-CRT、IMRT、RapidArc 3种计划方式的剂量学差异,为制定最佳PCI放疗方案提供指导.方法 选取10例SCLC患者颅脑CT,分别设计3D-CRT、IMRT及RapidArc 3种放疗计划.根据剂量体积直方图,评价靶区的D2％、D98％、V95、V100、均匀性指数（HI）、适形性指数（CI）以及危及器官（OAR）受量,比较机器跳数（MU）的差异.结果 IMRT及RapidArc的靶区剂量学参数（CI、HI、D2％、D98％、V95、V100）均优于3D-CRT,差异有统计学意义（p＜0.05）.IMRT、RapidArc较3D-CRT显著降低左右视神经Dmax、左右腮腺Dmean及脑干Dmax的受量,差异有统计学意义（P＜0.05）;相反,3D-CRT能显著减少左右晶状体的Dmax和左右眼球的Dmax、Dmean受量,差异有统计学意义（P＜0.05）.IMRT及RapidArc在靶区和危及器官受量方面无差异.3D-CRT、IMRT和RapidArc计划的平均MU分别为287.8、1388.8和346.6.结论 IMRT及RapidArc较3D-CRT具有一定的剂量学优势,3D-CRT能减少晶状体及眼球的受量,治疗时间短.

Objective To compare the dosimetric differences among three-dimensional conformal radiotherapy（3D-CRT）,intensity-modulated radiotherapy（IMRT）and RapidArc for prophylactic carnial irradiation（PCI）in small cell lung cancer（SCLC）patients.Methods Ten patients with SCLC were enrolled into this study.3D-CRT,9-field IMRT（IMRT）and double arc RapidArc plans were designed and optimized for each patient.The goal was to deliver 25 Gy to ≥ 95% of the planning target volume（PTV）while the same normal-tissue dose constraints were achieved.The dose distribution and conformal index （CI）,homogeneity index（HI）of target volume,the maximum dose（D2 %）,the minimum dose（D98 %）,target coverage of PTV（V95 and V100）,and Dmean and Dmax of organs at risk（OAR）were analyzed by using the dose volume histogram（DVH）.The monitor units and delivery time were also evaluated.Results All plans met the clinical requirements.PTV dosimetric parameters（CI,HI,D2%,D98%,V95 and V100）of RapidArc and IMRT were superior to those of 3D-CRT with significant difference（P〈0.05）.The maximum doses to the optic nerves,brainstem and the mean dose to the parotid glands of the IMRT and RapidArc plans were all significantly lower than those of the 3D-CRT plan（P〈0.05）,while 3D-CRT plan provided the lowest maximum doses and mean dose of the lens and eyes（P〈0.05）.Compared with IMRT plan,no obvious advantage in PTV dosimetric parameters could be observed in RapidArc plans.In terms of organ sparing,no statistical difference was observed between IMRT and RapidArc plans.The number of monitor units for 3D-CRT,IMRT and RapidArc were 287.8,1388.8 and 346.6,respectively.Conclusions Compared with 3D-CRT,IMRT and RapidArc show better dosimetric quality.The 3D-CRT plan has a significantly lower dose on the lens and eyes,less MU and shorter delivery time than IMRT and RapidArc plans.