立体定向放射外科Zap-X与CyberKnife治疗单发脑转移瘤的剂量学比较

Dosimetric comparison of Zap-X and CyberKnife stereotactic radiosurgery for single brain metastasis

目的评价立体定向放射外科(SRS)的Zap-X系统和射波刀(CK)G4系统治疗单发脑转移瘤的剂量学特性。方法回顾性选取12例已行CK治疗的单发脑转移瘤患者,计划靶区(PTV)的处方剂量为18~24 Gy,治疗1~3次。PTV为0.44~11.52 cm^(3)。应用Zap-X计划系统以相同的处方剂量和危及器官限量对该12例患者进行重新计划,且Zap-X和CK的PTV处方剂量均归一到70%。将两组计划的计划参数、靶区和危及器官相关参数进行比较并评价。所有数据均在MIM Maestro读取。应用配对Wilcoxon符号秩检验进行统计分析,P<0.05为差异有统计学意义。结果靶区的覆盖率方面,CK显著高于Zap-X(99.14%±0.57%∶97.55%±1.34%,P<0.01),但Zap-X的适形指数更高(0.81±0.05∶0.77±0.07,P<0.05),Paddick梯度指数较CK低(2.98±0.24∶3.15±0.38,P=0.117),剂量梯度评分指数(GSI)更高。Zap-X的总机器跳数(MU)显著低于CK(11627.63±5039.53∶23522.16±4542.12,P<0.01),并且治疗时间更短[(25.08±6.52)∶(38.08±4.74)min,P<0.01]。对于脑组织的受量,Zap-X的剂量体积显著低于CK(P<0.05)。Zap-X脑干的D_(mean)和D_(max)值较低(P<0.05),眼球和晶状体的D_(mean)和D_(max)较高。对于视神经和视交叉,两组计划之间没有差异。在对皮肤的保护方面(V_(22.5 Gy)),Zap-X比CK更好[(4.15±4.48)∶(4.37±4.50)cm^(3),P<0.05]。结论对于单发脑转移瘤的SRS治疗,Zap-X能够提供与CK相当的甚至更优的高质量计划,尤其是可以缩短治疗时间。随着Zap-X系统的不断完善和升级,Zap-X有可能成为治疗脑转移瘤的新SRS平台。

Objective To evaluate the dosimetric characteristics of Zap-X system and CyberKnife(CK)G4 system of stereotactic radiosurgery(SRS)for single brain metastasis.Methods Twelve patients with single brain metastasis had been treated with CK were selected retrospectively.The prescribed dose of planning target volume(PTV)was 18-24 Gy for 1-3 fractions.The PTV was ranged from 0.44 to 11.52 cm^(3).The 12 patients were re-planned in the Zap-X planning system using the same prescription dose and organs at risk constraints,and the prescription dose of PTV was normalized to 70%for both Zap-X and CK.The planning parameters and dosimetric parameters of PTV and organs at risk were compared and evaluated between two plans.All data were read at MIM Maestro.A paired Wilcoxon'signed-rank test was adopted for statistical analysis.A P value of less than 0.05 was considered as statistical significance.Results For the target coverage,CK was significantly higher than Zap-X(99.14±0.57%vs.97.55±1.34%,P<0.01),but Zap-X showed a higher conformity index(0.81±0.05 vs.0.77±0.07,P<0.05),a lower Paddick gradient index(2.98±0.24 vs.3.15±0.38),and a higher gradient score index(GSI)than CK.The total monitor unit(MU)of Zap-X was significantly lower than that of CK(11627.63±5039.53 vs.23522.16±4542.12,P<0.01)and the treatment time was shorter than that of CK[(25.08±6.52)vs.(38.08±4.74)min,P<0.01].Zap-X had lower dose volumes than CK for the dose of brain(P<0.05).Zap-X had a lower D_(mean)and D_(max)of brainstem(both P<0.05),but a higher value of eyes and lens.For optic nerves and optic chiasm,there were no significant differences between two groups.In addition,for the protection of skin(V_(22.5 Gy)),Zap-X seemed better than CK[(4.15±4.48)vs.(4.37±4.50)cm^(3),P<0.05].Conclusions For SRS treating single brain metastasis,Zap-X could provide a high quality plan equivalent to or even better than CK,especially reducing the treatment time.With continuous improvement and upgrading of Zap-X system,it may become a new SRS platform for the treatment of brain metastasis.