直肠癌术前固定野动态调强与不同能量容积旋转调强的剂量学差异

Dosimetric comparison between fixed-field intensity-modulated radiotherapy and volumetric modulation arc therapy with different energy photons for preoperative radiotherapy in rectal cancer

目的探讨固定野动态调强(c-IMRT)与不同能量容积旋转调强(VMAT)技术在直肠癌术前放疗中的剂量学差异。方法选取18例直肠癌术前患者,在Eclipse 10.0计划系统上分别进行6 MV 5野c-IMRT和6 MV、10 MV单弧VMAT三组计划设计。PTV处方剂量为50 Gy/25次,2 Gy/次。在95%体积的PTV达到处方剂量前提下,比较三组计划的剂量体积直方图(DVH)、靶区和危及器官剂量、适形度指数(CI)、均匀性指数(HI)、正常组织低剂量体积(B-P)、机器跳数(MU)及治疗时间(TT)。结果VMAT的靶区适形度指数(CI)比c-IMRT略低(P>0.05),10 MV VMAT的均匀性指数(HI)、V105与c-IMRT相似(P>0.05),均显著优于6 MV VMAT(P<0.05)。在VMAT计划中小肠的Dmean、V50略高于c-IMRT(P>0.05),其Dmean、D5、V40 10MV VMAT显著低于6 MV VMAT(P<0.05)。膀胱的Dmean、D5、V30较c-IMRT显著高(P<0.05),在D5的保护上10 MV VMAT显著优于6 MV VMAT(P<0.05)。双侧股骨头的Dmean、V20、V30明显低于c-IMRT(P<0.05)。相对于VMAT来说,B-P的V5、V10显著高于c-IMRT,V20显著低于c-IMRT(P<0.05),其中V10、V15、V20 10MV VMAT较6 MV VMAT显著低(P<0.05)。MU:6 MV VMAT(365±21)和10 MV VMAT(427±53)分别较c-IMRT(940±177)减少了61%、55%(P<0.05)。TT:6 MV VMAT(67±3)s和10 MV VMAT(72±6)s分别较c-IMRT(247±28)s减少了73%、71%(P<0.05),10 MV VMAT比6 MV VMAT增加了7%(P<0.05)。结论 VMAT可以达到或优于c-IMRT的靶区剂量分布,10 MV VMAT能更好地保护小肠、膀胱和双侧股骨头,同时明显减少MU与TT。

Objective To compare the dosimetry between fixed-field intensity-modulated radiotherapy（IMRT） and volumetric modulation arc therapy（ VMAT） with different energy photons in the preoperative radiotherapy of rectal carcinoma.Methods The 5-field IMRT plans of 6 MV and single arc VMAT of 6 MV and 10 MV plans were designed to 18 rectal cancer patients with preoperative radiotherapy by planning treatment system（ Eclipse 10.0）,respectively. Dose prescription was 50 Gy in 25 fractions. All plans were normalized to 50 Gy to95% of PTV. The dose volume histogram（ DVH）,target and risk organ doses,conformity indexes（ CI）,homogeneity indexes（ HI）,low dose volume of normal tissue（ B-P）,monitor units（ MU） and treatment time（ TT） were compared among the three kinds of plans.Results CI of VMAT was little lower than that of c-IMRT（ P〈0.05）. HI,V105 of 10 MV VMAT were similar to c-IMRT（ P〈0.05）,but were better than those of 6 MV VMAT. The Dmean and V50 of small intestine in VMAT plans were higher than those in c-IMRT plans（ P〈0.05）,however,the Dmean,D5 and V40 in 10 MV VMAT were lower than those in 6 MV VMAT（ P〈0.05）. The Dmean,D5,V30 of bladder in VMAT plans were higher than those of c-IMRT plans（ P〈0.05）. In term of the protection of D5,10 MV VMAT was superior to the 6 MV VMAT（ P〈0.05）. The Dmean,V20 and V30 of femoral head in VMAT plans were significantly lower than those in c-IMRT plans（ P〈0.05）. VMAT plans had higher B-P V5,V10 and lower V20（ P〈0.05） as compared with c-IMRT plans（ P〈0.05）,and the V5,V10,V20 of B-P 10 MV VMAT plans were lower to the 6 MV VMAT plans（ P〈0.05）. 6 MV VMAT plans and 10 MV VMAT plans reduced the monitor units（ MU） by61% and 55%（ 365±21 vs 427±53,P〈0.05）,as well as the TT by 73% and 71%[（ 67±3） s vs（ 72±6） s,P〈0.05],as compared with cIMRT plans[MU： 940± 177,TT：（ 247 ± 28） s]. Conclusions Both VMAT and c-IMRT plans could satisfactorily meet the requirement of clinical dosimetry. But in a single arc VMAT plans,10 MV has better target coverage for small intestine,bladder and femoral head and could reduce MU and TT.