鼻咽癌调强放射治疗锁野计划对低剂量区的影响

Impact of fixed-jaw field intensity modulated radiotherapy(IMRT) on low dose area of nasopharyngeal carcinoma

目的:通过比较鼻咽癌调强放疗中锁野计划和分野计划的剂量学差异,探讨锁野对低剂量区的影响,为临床放疗方案的选择提供参考依据。方法:选取10例鼻咽癌患者分别制定9野的锁野调强和分野调强计划,比较机器跳数、靶区Dmean、脑干Dmax、脊髓Dmax、晶体Dmax、腮腺Dmean、口腔Dmean以及body V5、V10、V20、V30、V40、V50、Dmean等参数的剂量学差异。结果:两种计划均满足临床需求。各计划靶区(PTV)的Dmean参数值相差甚微,且无统计学差异。而对于MU锁野计划值明显低于分野计划值,且统计具有显著性差异(P<0.001)。对于脑干和脊髓最大剂量值锁野计划稍低于分野计划,但均无统计学差异。对于左右腮腺平均剂量值,锁野计划稍低于分野计划,也均无统计学差异。然而对于左右晶体最大剂量值,锁野计划明显高于分野计划,且具有统计学差异(P=0.010和0.021)。对于口腔平均剂量值,锁野计划稍高于分野计划,但均无统计学差异。对于Body剂量,锁野计划均低于分野计划。V20、V30和V40差异具有统计学意义(V20:P=0.005;V30:P=0.027;V40:P=0.046)。然而对于Dmean、V5、V10和V50差异无统计学差异(Dmean:P=0.697、V5:P=0.084和V50:P=0.911)。结论:锁野计划可以减少MU值,减少治疗时间和减少低剂量区。

Objective:To compare the dosimetric difference between fixed-jaw plan and split-field plan used for IMRT treatment of nasopharyngeal carcinoma,and to investigate their impact on the low dose ar-ea.Methods:CT images of ten patients with nasopharyngeal carcinoma were studied.Split-field plan,and fixed-jaw plan were performed on an Eclipse 13.5 TPS.Dosimetric parameters of PTV,heterogeneity index(HI),number of monitor units(MUs),and dose volume values of the body,brain stem Dmax,spinal cord Dmax,crystal Dmax,left and right parotid Dmean,and oral Dmean were obtained from dose volume histogram.Results:Two plans met clinical requirements.There was little difference between the mean parameters and HI values of each PTVs,and there was no statistical dif-ference.For MU of the fixed-jaw plan value of lock field was significantly lower than that of split-field plan,and the statistical analyse showed significant difference(P<0.001).For the maximum dose of left and right crystals,the fixed-jaw plan values were significantly higher than split-field plan values(P=0.010 and 0.021).For brain stem Dmax,spinal cord Dmax,left and right parotid Dmean in the fixed-jaw plan value were slightly lower than those in the split-field plan,but there were no statistical difference.However,for the Dmax of left and right crystals,the fixed-jaw plan values were signifi-cantly higher than the field-splitting plan values(P=0.010 and 0.021).For body,the fixed-jaw plan values were lower than those in the splitting field plan.There were significant differences in V20,V30 and V40(V20:P=0.005;V30:P=0.027;V40:P=0.046).And there was no significant differ-ence in Dmean,V5,V10,and V50(Dmean:P=0.697;V5:P=0.084;V50:P=0.911).Conclusion:The fixed-jaw plan could reduce MU value,treatment time,and low dose area.