准直器角度优化对胃癌调强放疗计划影响

Influence of collimator angle optimization on intensity-modulated radiotherapy planning for gastric cancer

目的探讨4种准直器角度优化技术对胃癌调强放疗计划靶区(PTV)及危及器官(OAR)剂量学的影响。方法选取2015-2016年间武汉大学中南医院接受调强放疗的10例胃癌患者,调强放疗计划均采用常规5个野(330°、10°、45°、90°、180°),其他优化参数一致。在Eclipse计划系统中分别用4种不同的准直器角度优化技术设计调强放疗计划。准直器角度优化技术包括准直器角度设为默认0°(CL0)、与0°垂直的90°(CL90)、采用Eclipse自动角度优化(CLA)以及将准直器角度设为X-Jaws围绕靶区PTV距离最短时的角度(CLX)。主要剂量学参数包括PTV适形指数(CI)、均匀指数(HI)、平均剂量(Dmean)及OAR受量,并且考虑治疗时间(Time)、治疗跳数(MU)、控制点(CP)、分野数(SF)及适形距离(Fx)等参数。结果以CL0优化为对照,4种准直器角度优化技术PTV的CI、HI及Dmean比较差异无统计学意义(P>0.05),然而CLX能显著增加靶区PTV的Dmean(P<0.05);CLX优化能够减少肝(V30减少1.54%)、左肾(V12减少1.46%)等受量,但会轻微增加小肠和脊髓的最大剂量(<1%),而CL90与CLA优化会导致增加胃受量。4种不同的准直器角度优化中,CLX优化能够减少MU (减少25.02%)、CP (减少26.03%)、Fx (减少20.27%)及SF (平均减少1.3个分野)。对于Time,CLX相对减少10.03%;CL90与CLA能够减少MU、CP、Fx和SF,且CL90在减少Time方面有一定的优势,而CLA会相对增加Time (增加5.04%)。结论在胃癌的调强放疗计划中,采用CL90、CLA和CLX 3种准直器角度优化技术能够获得与常规CL0的准直器角度优化相当的剂量分布,且能减少MU,从而减少漏射和照射时间,提高治疗效率。

Objective To investigate the impact of four different collimator angle optimization techniques on the planning target volume (PTV) and organ at risk (OAR) during intensity-modulated radiotherapy (IMRT) for gastric cancer.Methods Ten patients with gastric cancer undergoing IMRT in Zhongnan Hospital of Wuhan University from 2015 to 2016 years were recruited in this study. All IMRT plans were designed by conventional five fields (330°,10°,45°,90°and 180°).In the Eclipse treatment planning system,four different collimator angle optimization techniques with consistent planning optimization parameters were employed to design the IMRT plan. Collimator angle optimization techniques included the following aspects. The collimator angle was set at 0 degree (CL0),collimator angle was set at 90 degree (CL90),Eclipse automatic collimator angle optimization (CLA) was adopted and collimator angle was set as the angle when the distance between X-Jaws and PTV (CLX) was the shortest. The dosimetric parameters mainly included the conformal index (CI) of PTV,the homogeneity index (HI),the mean dose (Mean),and the dosage of OAR.The treatment time (Time),monitor unit (MU),control point (CP),split field (SF) and conformal distance (Fx) were also considered.Results Regarding CL0 as the control,the CI,HI and Mean did not significantly differ among four collimator angle optimization techniques (all P>0.05),whereas CLX could significantly increase the average dose of PTV in the target area (P<0.05);CLX optimization reduced the liver(V30 reduction by 1.54%),left kidney(V12 decrease by 1.46%),right kidney and other OARs,whereas it slightly increased the maximum dose of the small intestine and spinal cord (<1%).CL90 and CLA optimization elevated the dose of OAR in gastric cancer. Among four different collimator angle optimization techniques,CLX optimization reduced the MU (25.02%),CP (26.03%),Fx (20.27%) and SF (by 1.3 separate fields on average) and treatment time (10.03%).CL90 and CLA optimization could decrease the MU,CP,Fx and SF.CL90 optimization had certain advantages in shortening the treatment time,whereas CLA optimization could prolong the treatment time by 5.04%.Conclusions During IMRT for gastric cancer,CL90,CLA and CLX collimator angle optimization techniques can obtain comparable dosimetry distribution to CL0 optimization technique,which can reduce the MU,decrease the radiation leakage,shorten the treatment time and improve treatment efficiency.