宫颈癌二弧旋转容积调强与固定7野动态调强的剂量学比较

Volumetric modulated arc therapy with double arcs vs seven-field fixed-gantry dynamic intensity modulated radiotherapy in cervical cancer:a dosimetric study

目的比较二弧旋转容积调强（volumetric modulated arc therapy，VMAT）与固定7野动态调强（dynamic intensity modulated radiotherapy，dlMRT）在宫颈癌放疗计划中的剂量学差异，寻找宫颈癌放疗的最佳计划方案。方法10例宫颈癌患者利用VARIAN计划系统（Echpse 8.6）分别制定二弧VMAT和7野dlMRT放疗计划。比较两种计划中靶区、射野内正常组织以及危及器官的剂量学差异和执行两种计划所需的机器条数（MU）、照射时间及计划制定优化时间的差别。结果与7野dlMRT相比，二弧VMAT靶区适合度指数（CI）更接近1（P〈0.05）、靶区剂量均匀性指数（HI）无显著差异；D100%显著大于7野dlMRT放疗计划，且Dmin更接近处方剂量，差异均有统计学意义（P〈0.05）。在二弧VMAT计划中股骨头的D…显著低于7野dlMRT计划（P〈0.05），而D5。两者接近。在小肠、膀胱、直肠和马尾的保护上二弧VMAT较7野dlMRT无明显优势，但仍能很好地达到临床要求。二弧VMAT总MU为7野dIMRT的1／4，治疗时间减少2／3。结论二弧VMAT计划可以达到或优于7野dlMRT计划的靶区剂量分布，能更好地降低部分危及器官的受照剂量，使正常组织内高剂量区（20～30Gy）体积明显减少，并且具有相对减少总MU、总治疗时间的优势，是宫颈癌放射治疗计划的较好选择之一。

Objective To compare the dosimetric difference between volumetric modulated arc therapy （VMAT） with double arcs and seven-field fixed-gantry dynamic intensity modulated radiotherapy （dlMRT） in the treatment of cervical cancer for the best plan of radiotherapy. Methods Based on the Varian radiation treatment planning system （ Eclipse 8.6） , 2 arcs of VMAT plans and 7 fields of dlMRT plans were generated in 10 patients with cervical cancer, respectively. Dose volume histograms were used to compare the target volume, normal tissue and organs at risks in the radiation field. Machine number （MU） , irradiation time and optimization time were evaluated to assess plan quality. Results Compared to dlMRT, conformity index （CI） of VMAT was closer to 1 （ P 〈 0.05）, and D100% were significantly greater and Dmin were closer to the prescription dose （ P 〈 0.05 ）, but there was no significant difference in evenness index （HI）. D of caput femoris were significantly lower in VMAT than in dlMRT（ P 〈 0.05 ）, while D5% was similar in the 2 planning. There was no difference in the protection of small intestine, bladder, rectum and eauda equine between VMAT and dlMRT, but the both of them reached the clinical requirement. The MU of VMAT was a quarter of that of dIMRT, and the treatment time was only a third of that of dlMRT. Conclusion Compared to the dIMRT, VAMT shows a better effect in target dose distribution, reduces the irradiation doses on organs at risk, and decreases the volume of high-dose area （20 to 30 Gy） in normal tissues, with the advantages of less MU and shorter overall treatment time. It is a better option for the development direction of cervical cancer radiotherapy.