减少肺癌螺旋断层放疗计划低剂量区体积的研究

Pre-clinical study of reducing the low-dose-area of tomotherapy on lung cancer planning

目的 寻求一种在保证治疗计划临床可行的前提下减少正常肺组织低剂量区体积的肺癌螺旋断层放疗（tomotherapy）计划设计方法.方法 选取30例单侧肺内病灶的肺癌患者CT图像,根据对健侧肺采取不挡（对照）、1/4半挡、1/2半挡、半挡、1/4全挡、1/2全挡和全挡7种条件分别设计A、B、C、D、E、F和G共7组治疗计划,分析各组方案靶区的剂量学参数差异和减少双肺低剂量区（V5～V10）体积的优劣.结果 与A组比较,B、C、D、E组对靶区影响较小,剂量学参数差异均无统计学意义;F组靶区的中位剂量和平均剂量增加,均值在0.5 Gy以内;G组对靶区影响较大,适形度较差.除B组外,其余各组均能减少双肺低剂量区体积（V5：8.06％ ～ 45.26％;V10：6.21％ ～33.95％）;半挡组可减少双肺V20体积（1.71％ ～3.78％）,全挡组增加了双肺V20体积（2.07％ ～5.07％）.各组的单次治疗时间均有一定程度的增加（8.51％ ～79.22％）.结论 对健侧肺半挡可以有效减少双肺低剂量区体积,临床计划设计时可以结合单次治疗时间和患者的耐受状况加长半挡健侧肺的弧度;对部分健侧肺全挡条件较半挡更能有效减少双肺低剂量区体积,但全挡时弧度不宜超过健侧肺弧度的1/2.

Objective To seek a optimization method for lung cancer planning with Helical TomoTherapy for reducing the low dose area of total lung.Methods CT images of thirty patients with unilateral lung cancer were selected.Seven plans （Groups A,B,C,D,E,F and G） were generated for each patient using an identical optimization procedure with the conditions that implemented contralateral lung with unblocked （control group）,1/4 directional block,1/2 directional block,directional block,1/4 complete block,1/2 complete block and complete block,respectively.The benefits in different schemes of reducing the low dose area of normal lung tissue were estimated,in order to provide a reference treatment plan scheme in clinical.Results Groups B,C,D and E had less influence on the target than that of group A.And there were no statistical difference between the target dosimetric parameters.The median dose and average dose of group F were increased within 0.5 Gy.The conformal index of group G had great influence on the target.The low dose area of total lung were reduced effectively in Groups C,D,E,F and G,the average decrease of V5 and V10 was 8.06%-45.26% and 6.21%-33.95%,respectively.The V20 decreased by 1.71%-3.78% in directional block group,while V20 increased in complete block group （2.07%-5.07%）.The single treatment time was increased by 8.51%-79.22%.Conclusions The results showed that the low dose area of total lung was higher for the plan without any block limitation.It could reduce the low dose area of total lung with directional block.We should lengthen the blocking arc of contralateral lung with directional block based on the fractional treatment time and the patient＇s physical condition.A certain arc of contralateral lung with complete block could effectively reduce low dose area.When complete block was used,it is suggested that the arc was no more than half of the contralateral lung.