摆位误差对胰腺癌同步推量调强计划剂量分布的影响

目的 通过移动等中心模拟系统误差，探讨系统误差对胰腺癌同步推量调强放疗计划剂量分布的影响。方法 对9例胰腺癌患者制定同步推量调强放疗计划，在治疗计划系统中通过移动等中心，分别模拟三维6个方向（左、右、前、后、头、足）上3mm和5mm的系统误差。在不改变射野分布和权重的情况下，重新计算剂量分布。比较等中心移动前后放疗靶区和危及器官（OARs）的剂量分布变化。结果 与未位移组相比，各方向的摆位误差对临床靶区（CTV）外放形成的计划靶区（PTV-C）的Dmean、Dmin和V95剂量分布影响明显（P＜0.05），特别是当摆位误差达5mm时，但对Dmax和V105的影响较小（P＞0.05）；对大体肿瘤靶区（GTV）外放形成的计划靶区（PTV-G）剂量分布的影响主要表现在Dmean上，特别是在头、足、后方向上（P＜0.05），其余影响较小（P＞0.05）。对于CTV和GTV，除了向头、向后对CTV有影响外（P＜0.05），其余误差对两者的剂量分布影响很小（P＞0.05）。对于脊髓Dmax，对剂量分布影响最大的来自于后侧的摆位误差（P＜0.05）。除了向足侧对左肾无明显影响外，其余不论哪个方向，双侧肾脏的剂量分布均发生改变（P＜0.05）；对肝脏的影响主要发生在头、足及右侧方向的摆位误差（P＜0.05）。结论 胰腺癌同步推量调强放疗时，摆位误差对靶区的剂量分布影响较小，但对脊髓、肾脏及肝脏等OARs的影响较大，故在制定胰腺癌的调强放疗计划时，正常组织外放边界应引起足够重视。

The effect of set-up errors on dosimetric evaluation of synchronous boost intensity-modulated radiotherapy in pancreatic cancer

Objective The study was to determine the effect of set-up errors on dosimetric evaluation of synchronous boost intensity-modulated radiotherapy（SIB-IMRT） in pancreatic cancer according to simulated systematic set-up errors by moving the isocentre.Methods SIB-IMRT plan were generated in 9 patients with pancreatic cancer.The effects of set-up errors of 3 and 5 mm were simulated in the treatment planning system by moving the isocentre and then recalculated the dose distribution without changing the field fluence distributions.Dose distribution of target volume and organs at risk were compared before and after the shift of isocentre.Results Compared with non-mobile group,a significant effect of set-up errors in all 6 directions were obtained for D Dmin and V95of planning target volume of clinical target volume（PTV-C）,particularly more than 5mm（P 〈 0.05）.No significant change was obtained for Dmnx and V105 （P 〉 0.05）.A significantly effect of set-up errors in the direction of caudal,cranial,superior were obtained for D of planning target volume of gross target volume（PTV-G）.Others has little effect （P 〉 0.05）.For clinical target volume （CTV） and gross target volume （GTV）,others＇ set-up errors have little effect except for the directions of superior and caudal（P 〉 0.05）.For spinal cord D the greatest influence was from the posterior set-up errors （P 〈 0.05）.Except for the cranial set-up errors,bilateral renal dose distributions changed significantly（P 〈 0.05）.A significant effect of set-up errors in the direction of cranial,caudal and right were obtained for liver（P 〈 0.05）.Conclusion For SIB-IMRT in pancreatic cancer,there was a little effect of set-up errors on dose distribution of target volume,but greater effect on organs at risk such as spinal cord,bilateral kidney and liver,This mentioned that the margin of organs at risk should be paid more attention when SIB-IMRT in pancreatic cancer was worked out.