Halcyon2.0医用直线加速器胸部调强放射治疗计划射野复杂度指标与剂量验证的相关性研究

Study on the correlation between the dose verification and the indicator of complexity of the IMRT field of Halcyon2.0 medical linear accelerator on chest

目的:比较Halcyon2.0医用直线加速器在胸部固定野调强放射治疗(FF-IMRT)计划中双层多叶准直器(MLC)之间的射野复杂度差异,探索基于双层MLC计算的射野复杂度指标和剂量验证结果之间的相关性。方法:选取医院收治的67例胸部放射治疗患者的Halcyon2.0FF-IMRT计划,使用电子射野影像系统(EPID)进行PortalDosimetry(PD)剂量验证。分别计算远源端MLC和近源端MLC的平均调制复杂度分数(MCS)、平均射野面积(BA)、平均射野不规则度(BI)、平均射野小孔径分数SAS_(2mm)、SAS_(5mm)、SAS_(10mm)、SAS_(15mm)和平均射野周长面积之比(C/A)5种射野复杂度指标。分析比较近源端MLC和远源端MLC之间的射野复杂度指标差异,并将射野复杂度指标和PD验证得到的γ通过率进行Spearman相关性检验。结果:基于远源端MLC计算的MCS小于近源端MLC,且基于远源端MLC计算的BI、SAS_(2mm)、SAS_(5mm)、SAS_(10mm)、SAS_(15mm)和C/A均大于近源端MLC,差异有统计学意义(Z=-4.148,Z=-6.347,Z=-7.115,Z=-6.915,Z=-6.041,Z=-5.079,Z=-6.359,P<0.05)。1%/1 mmγ分析标准下,近源端MLC的SAS_(15mm)与γ通过率均呈现出强相关性(|r|>0.7,P<0.05),近源端和远源端MLC的C/A也均和γ通过率呈现强相关性(|r|>0.7,P<0.05)。2%/2 mmγ分析标准下,近源端和远源端MLC的BA、SAS_(2mm)、SAS_(5mm)、SAS_(10mm)、SAS_(15mm)、C/A均与γ通过率均呈现中度相关性(0.4≤|r|≤0.7,P<0.05)。结论:射野复杂度指标中除远源端MLC的BI外均与PD验证的γ通过率具有不同程度的相关性,其中SAS和C/A的相关性较为明显,可在剂量验证前辅助物理师识别Halcyon2.0过于复杂的胸部计划。

Objective:To compare the difference of complexity of the field between dual-layer multi-leaf collimator(MLC)of the fixed field intensity-modulated radiotherapy(FF-IMRT)plan of Halcyon2.0 medical linear accelerator on chest,so as to explore the correlation between the indicators of the complexity of field based on the calculation of dual-layer MLC and the results of the dose verification.Methods:The Halcyon2.0 FF-IMRT plans of 67 patients who underwent radiotherapy on chest in Peking Union Medical College Hospital were selected,and electronic portal imaging device(EPID)was used to conduct verification of portal dosimetry(PD).A total of five kinds of indicators of complexities of field included the average modulation complexity score(MCS)of MLCs at the far-end and at the near-end of source,the average beam area(BA),the average beam irregularity(BI),the average small aperture score(SAS_(2mm),SAS_(5mm),SAS_(10mm),SAS_(15mm))of field and the average ratio of circumference to area(C/A)of field were respectively calculated.The difference of the complexity indicator of field between MLC at the far-end of source and MLC at the near-end of source was analyzed and compared,and Spearman analysis was adopted to test the correlation between complexity indicator of field andγpassing rates obtained from PD verification.Results:The MCS based on the calculation of MLC at the far-end of source was significantly smaller than that of MLC at the near-end of source,and the BI,SAS_(2mm),SAS_(5mm),SAS_(10mm) and SAS_(15mm) that based on the calculation of MLC at the far-end of source were significantly larger than those that based on the calculation of MLC at the near-end of source(Z=-4.148,Z=-6.347,Z=-7.115,Z=-6.915,Z=-6.041,Z=-5.079,Z=-6.359,P<0.05),respectively.Under the criteria of 1%/1mmγanalysis,the results of the correlation analysis showed that the SAS_(15mm) of MLC at the far-end of source appeared strong correlation withγpassing rate(|r|>0.7,P<0.05).and the C/As both MLCs at the near-end and the far-end of source appeared strong correlations withγpassing rate(|r|>0.7,P<0.05).Under the criteria of 2%/2mmγanalysis,the BA,SAS_(2mm),SAS_(5mm),SAS_(10mm),SAS_(15mm) and C/A both MLCs at the near-end and the far-end of source appeared moderate correlations withγpassing rates(0.4≤|r|≤0.7,P<0.05).Conclusion:In the indicators of complexities of field that is calculated by this study,each indicator has different degree of correlation withγpassing rate that is verified by PD except BI of the MLC at the far-end of source.The correlations of SAS and C/A of them are relatively obvious,which can be used in auxiliary recognition for excessively complex plan of Halcyon2.0 on chest before dose verification.