两种射野边界外扩方法在乳腺癌保乳术后容积旋转调强计划中的剂量学比较研究

Dosimetry comparison of two kinds of margin expansion methods of treatment field in VMAT for breast cancer after breast-conserving surgery

目的:针对乳腺癌容积旋转调强放射治疗(VMAT)计划,比较“Auto-Flash”功能和“假组织补偿法”两种射野边界外扩方法的剂量学差异,并评价其外扩效果。方法:选取医院收治的20例女性乳腺癌保乳术后患者,在对患者所有的VMAT计划中分别采用“Auto-Flash”功能和“假组织补偿法”进行射野边界的外扩,并根据两种皮肤通量射野边界方法外扩设计A-VMAT和P-VMAT两种治疗计划。评估两种计划的射野边界外放效果,靶区和危及器官(OAR)的剂量学参数,计划的执行效率及计划的剂量验证通过率。结果:在射野方向观察胸廓外放射野效果,两种计划的通量均已在胸廓方向外放到皮肤以外。A-VMAT和P-VMAT计划的靶区均匀性指数(HI)分别为0.07±0.011和0.08±0.002,差异有统计学意义(t=-5.661,P<0.05)。靶区适形指数(CI)差异无统计学意义。A-VMAT和P-VMAT计划靶区的98%靶区体积所受照射剂量(D_(98))分别为(5007.25±34.79)cGy和(4973.43±44.57)cGy,D_(2)分别为(5363.87±34.16)cGy和(5393.95±40.86)cGy,两种计划比较差异有统计学意义(t=3.465,t=-4.248;P<0.05)。靶区的D_(50)和平均剂量(D_(mean))以及主要OAR的剂量学参数基本相似,差异无统计学意义,且均能满足临床要求。结论:在乳腺癌保乳术后的VMAT计划中,采用“Auto-Flash”功能和“假组织补偿法”均能实现射野边界的有效外扩,且靶区剂量和OAR受量均能满足临床要求。“假组织补偿法”的射野边界外扩方法,可为尚无射野边界自动外扩功能的计划系统进行乳腺癌VMAT计划设计提供参考。

Objective:To compare the dosimetric differences between two kinds of margin expansion methods of treatment field in volumetric modulated arc therapy(VMAT) plan for breast cancer,and evaluate the expansion effect of that.Methods:Twenty patients with breast cancer after breast-conserving surgery who admitted to hospital were selected.The all VMAT plans of patients were performed external expansion for the margin of treatment field by adopting “Auto-Flash” function and “pseudo-bolus compensation” method,respectively.The two kinds of therapy plans(A-VMAT and P-VMAT) were externally designed according to two kinds of treatment field margin methods of skin fluuence.The external effect of treatment field margin,the dosimetric parameters of target volume and organs at risk(OAR),execution efficiency and passing rate of dose verification of plans between two kinds of plans were assessed.Results:On the beam eyes view(BEV),it was observed that the fluences in both groups were extended outside the skin along the anterior-posterior direction of the thorax.The homogeneity indexes(HI) of target volume of A-VMAT and P-VMAT were 0.07±0.011 and 0.08±0.002,respectively,and the difference of that between them was significant,but it was not obvious.The difference of conformity index(CI) between two groups was no significant.And the D_(98) of A-VMAT and P-VMAT were 5007.25±34.79 cGy and 4973.43±44.57 cGy,and the D_(2) of them were 53663.87±34.16 cGy and 5393.95±40.86 cGy,respectively,and the differences of them between two kinds of plans were significant(t=3.465,t=-4.248,P<0.05).The D_(50),D_(mean) and dosimetric parameters of major OAR were basically similar,and the differences of them was not statistically significant,and all of them could meet the clinical requirements.Conclusion:In VMAT after breast-conserving surgery for breast cancer,both “Auto-Flash” function and “pseudo-bolus compensation” method can realize the effective expansion of the treatment field margin,and both of the dose of target volume and received dose of OAR can meet the clinical requirements.Therefore,the margin expansion methods of treatment field of “pseudo-bolus compensation” can provide references for the plan system without automatic expansion function of treatment field margin to conduct the design of VMAT plan of breast cancer.