RapidArc与Novalis Knife在多发脑转移瘤SRS中的剂量学比较

Dosimetric comparison between RapidArc and Novalis Knife in stereotactic radiosurgery for multiple brain metastases

目的:比较基于多叶准直器的RapidArc与基于圆形限光筒的Novalis Knife在多发脑转移瘤立体定向放射外科(SRS)中的剂量学差异。方法:选取10例已进行Novalis Knife治疗的多发脑转移瘤患者(转移瘤3~5个/人),共37个转移瘤。重新设计单中心、非共面4弧的RapidArc SRS计划,靶区处方剂量统一为16 Gy。比较Novalis Knife计划和RapidArc SRS计划中靶区的剂量适形度指数和均匀性指数、靶区周围剂量梯度指数、正常脑组织等剂量线体积(V16、V12、V9、V6、V3)以及治疗所需的机器跳数。结果:RapidArc SRS计划相较于Novalis Knife计划,适形度指数更接近于1(0.79±0.10 vs 0.50±0.22,P=0.000),均匀性指数更接近于0(0.07±0.01 vs 0.15±0.07,P=0.000),但靶区周围剂量梯度指数较大(15.92±12.43 vs 5.05±3.53,P=0.000)。对于正常脑组织等剂量线体积,RapidArc SRS计划中V16明显小于Novalis Knife计划(P=0.005);两计划的V12、V9无明显差异(P=0.445,0.059);而RapidArc SRS计划中V6、V3明显大于Novalis Knife计划(P=0.005,0.005)。RapidArc SRS计划的机器跳数明显少于Novalis Knife计划(P=0.005)。结论:RapidArc SRS计划通过设置单一治疗等中心可实现颅内多个转移瘤的同步放射外科治疗,具有更高的靶区剂量适形度及均匀性;但靶区周边剂量跌落陡度不及Novalis Knife计划,正常脑组织低剂量受照范围较大。治疗依从性较差的多发脑转移患者可考虑选择治疗效率更高的RapidArc技术,并根据临床实际情况调整剂量分割模式,以减少放射损伤风险。

Objective To compare the dosimetric differences between two techniques,namely RapidArc based on multi-leaf collimator and Novalis Knife based on circular cone,in the stereotactic radiosurgery for multiple brain metastases.Methods Ten patients treated by Novalis Knife were enrolled in the study.Each patient had 3 to 5 brain metastases,and there were 37 brain metastases in total.The treatment plans of these cases were replanned with a single-isocenter and 4 non-coplanar RapidArc(RapidArc SRS plans),with the prescription dose for target areas standardized to 16 Gy.Dosimetric parameters,including the conformity index and homogeneity index of target areas,gradient index around target areas,the V16,V12,V9,V6 and V3 of normal brain tissues and monitor units were compared between Novalis Knife plans and RapidArc SRS plans.Results Compared with Novalis Knife plans,RapidArc SRS plans had a higher conformity index(0.79±0.10 vs 0.50±0.22,P=0.000),lower homogeneity index(0.07±0.01 vs 0.15±0.07,P=0.000)and higher gradient index(15.92±12.43 vs 5.05±3.53,P=0.000).The V16 of normal brain tissues in RapidArc SRS plans was obviously lower than that in Novalis Knife plans(P=0.005).There was no significant difference between two kinds of plans in the V12 and V9 of normal brain tissues(P=0.445,0.059).However,the V6 and V3 of normal brain tissues in RapidArc SRS plans were significantly higher than those in Novalis Knife plans(P=0.005,0.005).Moreover,compared with Novalis Knife plans,RapidArc SRS plans were associated with markedly reduced monitor units(P=0.005).Conclusion RapidArc SRS plans can achieve the simultaneous treatment of multiple brain metastases by setting a single-isocenter,with higher conformity index and lower homogeneity index of target area;but compared with Novalis Knife plans,RapidArc SRS plans have a worse gradient index and a larger low-dose coverage range.The patients with multiple brain metastases who have poor adherence to treatment can be treated by RapidArc which is more efficient,and fractional dose mode should be adjusted according to the clinical situation,thereby reducing the risk of radiation injuries.