多发脑转移瘤行固定野逆向调强放疗与γ射线立体定向放疗剂量差异

A dosimetric comparison between γ ray stereotactic radiotherapy and intensity modulated radiotherapy for multiple brain metastases

目的比较固定野逆向调强放疗(intensity modulated radiotherapy,IMRT)和γ射线立体定向放疗(Gamma ray stereotactic radiotherapy,γ-ray SRT)在脑多发转移瘤中的剂量学差异。方法 10例脑转移瘤患者入组,肿瘤个数1~4个,基于10例患者的CT扫描图像分别制定γ-ray SRT计划和7野IMRT计划。处方剂量要求:5 Gy/次,共10次。所有计划要求至少95%靶区体积达到处方剂量,至少98%靶区体积达到95%的处方剂量;IMRT允许5%体积靶区剂量超过110%。通过剂量体积直方图(dose-volume histogram,DVH),比较两种技术的靶区剂量和正常组织的受照情况。结果两种计划均能达到治疗要求。其中,IMRT的靶区适形指数(CI)高于γ-ray SRT(t=-6.75,P<0.001),不均匀指数(HI)低于γ-ray SRT(t=13.94,P<0.001)。除V5无显著性差异外,全脑平均剂量、V10、V15、V20、V25、V30γ-ray SRT低于IMRT(t=-6.988^-2.685,P<0.05)。眼球、晶体、视神经、脑干受照剂量二者差异不大(t=-2.224^-1.128,P=0.04~0.289),且均未超过最大剂量限值。结论 IMRT和γ-ray SRT均能用于脑多发转移瘤的放射治疗,相比IMRT,γ-ray SRT能更好地降低正常脑组织的受照剂量,但靶区适形度较低,治疗时间较长。

Objective To evaluate the dosimetric characteristic and treatment efficiency of γ ray stereotactic radiotherapy （γ-ray SRT） with step-and-shoot intensity modulated radiotherapy （IMRT） for the hypofractionated stereotactic radiotherapy （HFSRT） in patients with multiple brain metastases. Methods The CT datasets of 10 patients with one to four brain metastases were selected in this study. Two plans were generated respectively for each case： seven-field step-and-shoot IMRT or γ ray stereotactic radiotherapy. The prescribed dose was 50 Gy in 10 fractions. For PTV, plans aim to achieve at least 95% of PTV was encompassed by the prescription dose, at least 98% of PTV was covered with the 95% of prescription dose, and an over-dosage of 110% of the prescription dose was allowed to 5% volume of the PTV for IMRT. Then ,the two techniques were compared each other by dose-volume histogram （DVH）. Results The plans generated using two techniques were clinically acceptable. The target conformal index（CI） in IMRT was higher than γ-ray SRT （t=-6.75,P〈0.001）,its homogeneity index （HI） belowed γ-ray SRT （t=13.94,P〈0.001）.The maximum doses of eyes, lens,optic nerves, brainstem between the two plans had no significant difference （t=-2.224--1.128,P=0.04-0.289）,and did not exceed the maximum dose limit. The percentage of healthy tissue volume receiving 10-30 Gy was larger with IMRT than with γ-ray SRT （t=-6.988--2.685,P〈0.05）,while the percentages of volume receiving 5 Gy was smaller with IMRT than with γ-ray SRT （t=-1.7,P=0.123）. Conclusion The plans generated using two techniques are clinically acceptable. Compared with IMRT, γ-ray SRT is better able to reduce radiation dose on normal brain tissue;but with lower target conformal,longer treatment time.