多叶准直器射野和独立准直器射野剂量学比较

目的探讨多叶准直器射野和独立准直器射野剂量学数据对放射治疗计划系统建模的影响。方法在Varianunique型直线加速器上对多叶准直器和独立准直器射野的百分深度剂量、射野离轴量以及总散射因子进行比较。结果两种射野的百分深度剂量差别不大，但射野离轴量以及射野总散射因子差别较大。多叶准直器形成的射野均比独立准直器形成的射野要大；随射野变小，两者总散射因子的差异越来越显著。结论在计划系统的建模过程中必须关注不同射野的剂量学数据差异，建议在调强计划系统建模过程中采用多叶准直器射野进行数据采集。

Comparison of Dosimetry of Radiation Fields Formed by Multileaf Collimator and Independent Collimator

Objective To evaluate the influence of dosimetry data of radiation fields formed by multileaf collimator and independent collimator on the commissioning of treatment planning system. Methods The percentage depth dose, the off-axis ratio and the total scattering factors of radiation fields formed by multileaf collimator and independent collimator were measured in Varian Unique linac respectively. Results There is no significant difference in the percentage depth dose of two kinds of fields. There are significant differences in the off-axis ratio and the total scattering factors of two kinds of fields. The sizes of radiation fields formed by multileaf collimator are larger than the sizes of radiation fields formed by independent collimator. The differences in the total scattering factors of two kinds of fields are more and more significant along with the decrease of field sizes. Conclusion We must pay close attention to the differences of dosirnetry data of radiation fields formed by multileaf collimator and independent collimator in the commissioning process of treatment planning system, which indicates that we should collect dosimetry data by using fields formed by multileaf collimator in the commissioning process of intensity-modulated treatment planning system.