放射性^(125)I粒子植入与外放疗治疗颈椎转移瘤剂量学对比分析

A dosimetric analysis of cervical metastases between radioactive ^(125)I seeds implantation and external beam radiation therapy

目的对比放射性^(125)I粒子植入与不同外放疗技术治疗颈椎转移瘤的靶区及危及器官剂量分布,为临床治疗方式选择提供依据。方法随机选取10例颈椎转移瘤患者,三维适形放射治疗(3D-CRT)计划为单前野加双侧斜后野,调强适形放射治疗(IMRT)为5野等分,选用2弧容积旋转调强放疗(VMAT)。将Oncentra治疗计划系统中的图像传输到粒子计划系统,制定近距离放疗(LDR)术前模拟计划。结果脊髓剂量相同时,LDR的D90和D95生物等效剂量(BED)分别为(184.15±25.84)Gy、(161.45±26.35)Gy。VMAT、IMRT、3D-CRT对应的靶区D95BED 2 Gy/f时分别为:(120.52±10.66)Gy、(119.19±10.91)Gy、(96.24±28.65)Gy;3 Gy/f时分别为:(122.19±7.54)Gy、(122.37±8.19)Gy、(95.94±24.70)Gy。靶区各参数与LDR相比,均服从正态分布,配对t检验差异具有统计学意义(P=0.00)。VMAT、IMRT与LDR比较,黏膜V5差异无统计学意义(P=0.16,0.34),只有3D-CRT高于LDR(P=0.00)。黏膜V30、DmeanLDR均低于3种外放疗技术(P=0.00)。其余甲状腺、腮腺、下颌骨各参数,LDR最低,差异具有统计学意义(P=0.00)。结论 3D-CRT、IMRT、VMAT单次2 Gy及3 Gy分割方案与LDR相比,脊髓剂量相同时,LDR的靶区剂量更高,同时有效地保护周围危及器官。对于放疗后复发的颈椎椎体转移瘤,LDR具有剂量学优势。

Objective To compare the gross tumor volume （GTV） and dose distributions for organs at risk （OAR） be- tween external beam radiation therapy （EBRT） and low-dose rate （LDR） brachytherapy in the treatment of cervical vertebral metastases, in order to provide the basis for clinical treatment. Methods A total of l0 patients were randomly selected. Three-dimensional conformal radiotherapy （3D-CRT） planning was a single forth one with two oblique radia- tion fields. Intensity modulated radiotherapy （IMRT） planning included five equal radiation fields, and 2-arc volumet- ric-modulated arc radiotherapy （VMAT） was adopted. The images from Oncentra treatment planning system （TPS） were delivered to Prowess TPS to formulate LDR brachytherapy pre-operative simulation plan. Results For the same dose of spinal cord, the biologically effective dose （BED） of D90 and D95 of LDR were （ 184.15 ± 25.84） Gy and （161.45±26.35 ） Gy. When the fraction scheme was 2 Gy/f, the D95 BED of VMAT, IMRT and 3D-CRT were （120.52 ±10.66） Gy, （119.19 ±10.91） Gy and （96.24 ±28.65） Gy. When the fraction scheme was 3 Gy/f, the D95 BED 3 Gy/f of VMAT, IMRT and 3D-CRT were （ 122. 19 ± 7.54） Gy, （ 122.37 ± 8. 19） Gy and （95.94 ± 24.70） Gy. All parameters complied with the normal distribution, P = 0.00 after paired t test. There was no statistical difference in V5 of the mucosa among VMAT, IMRT and LDR （P =0.16, 0.34）, and V5 of the mucosa of 3D-CRT was higher than that in LDR （ P = 0.00）. The V30 and Dmean of LDR were less than those of 3D-CRT, VMAT and IMRT, statistically （P = 0.00）. Other parameters of the thyroid gland, parotid gland and mandible were significantly different between LDR and 3D-CRT, VMAT and IMRT （ P = 0.00）. Conclusion When the fraction schemes were 2 Gy/f and 3 Gy/f, 3D-CRT, IMRT and VMAT had lower GTV doses than LDR, which could protect the OARs at the same time. Therefore, as to the cervical vertebral metastases after EBRT, LDR is a good choice for salvage treatment.