偏分野与均分野在容积调强治疗和调强放疗治疗鼻腔鼻窦癌中的剂量学比较

Dosimetric comparison of equispaced fields and non-equispaced fields in VMAT and IMRT for Nasal cavity and paranasal sinus cancer

目的比较调强放射治疗(IMRT)和容积调强治疗(VMAT)不同布野方式在鼻窦鼻腔癌放疗计划中剂量学差异,为临床治疗选择最佳方案提供参考依据。方法选取10例鼻窦鼻腔癌病例,分别进行IMRT 5野、7野偏分野、均分野和VMAT偏分弧、全弧共面计划设计,综合评估靶区的覆盖率、均匀性HI和适形性CI,危及器官受照剂量和治疗效率。结果 IMRT计划和VMAT计划均能满足临床上对靶区覆盖的要求,但VMAT的靶区覆盖较IMRT略高,且较IMRT的5野差异有统计学意义(P<0.05)。对PTV1的CI,VMAT(包括偏分弧和全弧)较IMRT(包括偏分野和均分野)更好。危及器官受照剂量中,脑干:VMAT较IMRT计划Dmax和D1%都较低,偏分弧D1%较全弧低;晶体、视交叉:VMAT较IMRT有相同或更好的保护效果,Dmax和D1%大部分更低;同侧视神经:VMAT较IMRT的Dmax低;同侧腮腺:VMAT较大部分IMRT的Dmean低;差异有统计学意义(P<0.05)。VMAT的平均机器跳数为IMRT的1/3;VMAT的偏分弧要比全弧跳数略低,差异有统计学意义(P<0.05)。结论IMRT的偏分野可作为鼻窦鼻腔癌放疗射野设计的考虑方案,在机器条件允许下,VAMT的偏分弧比IMRT偏分野更有优势。

Objective To compare dosimetric differences between intensity modulated radiotherapy( IMRT) and volumetric modulated arc therapy (VMAT) in the radiotherapy plan of nasal cavity and paranasal sinus cancer,provide reference basis for selecting the best clinical treatment.Methods Ten patients with nasal cavity and paranasal sinus cancers were selected.The patients were received the VMAT plans which were created as non-equispaced fields of VMAT and equispaced fields of VMAT,and IMRT plans which were created as non-equispaced fields and equispaced fields of 5 beams and 7 beams.Dosimetry of different design methods were compared to assess the coverage rate,heterogeneity index (HI) and conformity index (CI) in the target volum,exposure dose of the organs at risk and therapeutic efficiency.Result All of coverages of IMRT plans and VMAT plans met the criteria of clinic.VMAT plans were still better than IMRT plans,the differences between IMRT plans of 5 beams were significant.For CI of PTV1,VMAT (including partial arc and full arc) were better than IMRT(including non-equispaced fields and equispaced fields).Exposure dose of the organs at risk: for brain stem,Dmax and D1% of VMAT plans were lower than IMRT plans,and D1% of partial arc were lower than full arc (P<0.05).For Lens,VMAT plans had a same or better protective effect than IMRT plans,Dmax and D1% of VMAT plans were lower than most of those of IMRT(P<0.05).For Optic nerves-Ipsilateral,Dmax of VMAT plans were lower than those of IMRT (P<0.05).For Chiasm,Dmax and D1% of VMAT plans were lower than most of those of IMRT (P<0.05).For Parotid-Ipsilateral,Dmean of VMAT plans were lower than most of those of IMRT(P<0.05).Compared with IMRT plans,VMAT plans showed fewer MUs (about 1/3)(P<0.05).Conclusion Non-equispaced field can be considered as the radiotherapy field design of Nasal cavity and paranasal sinus cancer.Depending on the machine conditions,the partial arc of VMAT is more advantageous than the non-equispaced fields of IMRT.