晚期胸腺瘤精确放疗计划的剂量学对比研究

Dosimetric comparison among different precision radiotherapy plans for advanced malignant thymoma

目的放疗是不可手术切除的晚期胸腺瘤重要的姑息性治疗手段。本研究拟对比不可手术切除胸腺瘤三维适形调强放疗(IMRT)、容积旋转调强放疗(VMAT)及螺旋断层放射治疗(TOMO)的剂量学参数,为晚期胸腺瘤放疗技术的选择提供理论依据。方法选取本院9例接受姑息性放疗的晚期不可手术切除胸腺瘤患者,勾画放疗靶区及危及器官,传输至Raystation及TOMO计划系统,分别评估三组计划的等剂量曲线分布图、剂量体积直方图、均匀性指数、适形性指数以及危及器官受照剂量。结果三组计划均能够满足处方剂量要求及危及器官限量。PGTV,TOMO组等剂量曲线覆盖体积的适形性及剂量均匀性优于IMRT及VMAT组,TOMO组的中位V5为41.858%,小于IMRT组的45.9%,同时小于VMAT组的48.86%,TOMO组的中位V20为20.25%,小于IMRT组的23.78%。TOMO组心脏的中位V40为23.576%,明显小于VMAT组的27.81%。脊髓中位Dmax相比,TOMO组为37.65 Gy,小于IMRT组的38.39 Gy及VMAT组的39.6 Gy。结论不可手术切除的晚期胸腺瘤,与IMRT及VMAT相比,TOMO放疗计划具有更优的靶区适形性及剂量分布均匀性,并可减少双肺、心脏及脊髓的受照剂量。

Objective Radiotherapy is one of the most important palliative treatments for unresectable advanced malignant thymoma. The purpose of this study was to provide a theoretical basis for the selection of advanced malignant thymoma radiotherapy technology by comparing the dosimetric parameters of IMRT, VMAT and TOMO plans. Methods 9 patients with unresectable advanced malignant thymoma were retrospectively selected for this dosimetric study. Target volume and organs at risk(OARs) were delineated and transmitted to the Raystation and TOMO planning system. RTOG1106 was used for districting the doses to the OARs. The isodose curve, dose-volume histograms(DVHs), conformal index(CI), homogenecity index(HI) and the doses to the OARs were calculated in each treatment scheme.Results The three radiotherapy plans of 9 patients could suffice the demand of prescription dose and dose limits for OARs. For PGTV, the conformality and homogeneity dose distribution of the TOMO group were superior than those of the IMRT or VMAT groups. The median V5 to total lungs of TOMO group(V5=41.858%) was significantly decreased compared to plans by IMRT(V5=45.9%, P=0.038) and VMAT(V5=48.86%, P=0.015). The median V20 to total lungs was reduced by TOMO(V20=20.25%) compared to IMRT(V20=23.78%, P=0.0105). The median V40 to heart by TOMO(V20=23.576%) was significantly less than that by VMAT(V40=27.81%, P=0.025). The median of maximum doses to spinal cord was also reduced by TOMO(Dmax=37.65 Gy) when compared to IMRT(Dmax=38.39 Gy, P=0.021) or VMAT(Dmax=39.6 Gy, P=0.008), respectively.Conclusion TOMO plan for unresectable advanced malignant thymoma could achieve better conformal target coverage and homogeneity dose distribution than IMRT or VMAT. TOMO also provides better OARs protection than IMRT or VMAT.