叶片运动限制参数对容积旋转调强放疗的影响

Impact of constraint leaf motion parameter on volumetric modulated arc therapy

目的:研究叶片运动限制(constrain leaf motion,CLM)参数对容积旋转调强放疗(volumetric modulated arc therapy,VMAT)计划的质量、执行效率及执行精度等的影响,为临床中合理设定CLM参数提供参考。方法:选取某院2019年3—11月接受放疗的鼻咽癌患者20例,均使用Raystation计划系统设计VMAT计划,比较CLM值分别为0.15、0.30、0.50、0.65、0.85、1.10 cm/(°)时VMAT计划的子野面积、剂量学差异、出束时间、机器跳数及γ验证通过率。应用SPSS 18.0软件进行统计学分析。结果:随着CLM值的增大,所生成VMAT计划的小面积子野所占比例逐渐增大。靶区PTV7006(所有处方剂量为7006 cGy的靶区)的最大剂量D2(2%的体积所接受的剂量)、平均剂量Dmean、均匀性指数(homogeneity index,HI),靶区外的低剂量分布体积LD4000以及部分危及器官(脑干、脊髓、腮腺、视神经和视交叉)的受照剂量随CLM值变化均有统计学差异(P均<0.05),在CLM值≥0.50 cm/(°)时均有着更优的评估参数。出束时间在CLM值<0.50 cm/(°)时变化不大,但从0.50 cm/(°)开始,出束时间随CLM值的增大而明显增加(F=12.011,P=0.000)。机器跳数随CLM值的增大而呈近似线性的增长,差异显著(F=6.802,P=0.000)。3%/2 mm的γ通过率差异显著(F=8.032,P=0.000),随CLM值的增大而呈逐步下降的趋势,但在CLM值≤0.65 cm/(°)时均达到了容差限值95%以上。结论:CLM参数对VMAT计划的影响显著,CLM值的增大有助于提升计划的整体质量,但是会明显增加计划的机器跳数、降低计划的执行效率以及执行精度,建议临床上应将CLM值限定在0.50~0.65 cm/(°),以获取最优的VMAT计划。

Objective To investigate the effect of constraint leaf motion(CLM)parameter on the quality,execution efficiency and execution accuracy of volumetric modulated arc therapy(VMAT)to provide references for reasonable setting of CLM parameters in clinical practice.Methods Totally 20 nasopharyngeal carcinoma patients from March to November 2019 in some hospital were selected.The VMAT plans were designed with Raystation planning system,which had the parameters compared such as the sub field area,dosimetric difference,beam exit time,machine hops and gamma validation pass rate when CLM parameter was 0.15,0.30,0.50,0.65,0.85 and 1.10 cm/(°)respectively.SPSS 18.0 software was used for statistical analysis.Results As the CLM parameter rose the proportion of small-area subfields of the generated VMAT program increased progressively.CLM parameter changes resulted in significant differences between the maximum dose D2(2%of the volume received),the mean dose Dmean and the homogeneity index(HI)of PTV7006 target areas with the prescription doses higher than 7006 cGy,the low dose distribution volume LD4000 outside PTV7006 target areas as well as the exposure doses of some organs at risk(brainstem,spinal cord,parotid gland,optic nerve and optic chiasma),and all the P values were lower than 0.05.Better evaluation parameters were obtained when CLM parameter was not lower than 0.50 cm/(°);beam-on time had no obvious differences when CLM parameter was lower than 0.50 cm/(°),and got risen significantly with the increase of CLM parameter(F=12.011,P=0.000).The number of machine hops increased approximately linearly with the increase of CLM parameter(F=6.802,P=0.000).γpassing rates of 3%/2 mm had statistical differences(F=8.032,P=0.000),and decreased gradually with the increase of CLM parameter,which were all higher than 95%of the tolerance limit when CLM parameter was not higher than 0.65 cm/(°).Conclusion The CLM parameter has a significant impact on VMAT planning.Increasing the CLM helps to improve the overall quality of the plan,while significantly increases the number of hops,decreases the efficiency and accuracy of the plan execution.It's suggested the value of CLM parameter be limited between 0.50 and 0.65 cm/(°)in order to obtain optimal VMAT plan.