楔形因子对照射野大小和射线深度的影响分析

Analysis of the effect of the wedge factor on the field bulk and radial depth

目的照射野大小和测量深度不同,将导致楔形因子发生改变,继而使楔形照射野下的剂量计算发生偏差。方法利用德国WELLHOFER公司DOSE-1剂量仪和FC65-G指型电离室、水模(40 cm×40 cm×30 cm)分别测量6MV条件下不同深度、不同面积的平野和楔形野的剂量率,计算其楔形因子。结果深度对楔形因子的影响较明显,随着测量深度的增加楔形因子也增加,楔形板角度越大,深度对楔形因子的影响越明显,从1.5cm到10cm时楔形因子最大有2.5%的偏差。照射野大小对楔形因子也有一定的影响,随着照射野的增加,楔形因子也增加,只是程度有所不同。射野较小而深度较浅时,实测的楔形因子比标准值要小,射野较大且深度较深时,实测的楔形因子比标准值要大。结论用传统方法计算楔形野剂量存在误差,根据质量控制要求,楔形因子的精确度不能超过2%,为保证剂量计算的准确,消除计算误差,应测量并使用不同楔形野的楔形因子,同时对楔形因子做深度修正,采用相对深度的楔形因子,以达到放射治疗质量保证和质量控制规定的标准。

Objective Various fields and depth can result in the change of wedge factor. Then the mathematical dosage under wedge factor changes. Methods The dose rates of plane field and wedge field about various depth and area arecalculated using DOSE-1 Electrometers German WELLHOFER Limitation , FC65-G finger Ion chamber and water mould （40 cm× 40 cm× 30 cm）respectively. The wedge factor is also detected. Results The depth affects wedge factor significantly. Wedge factor is improved along with the rising depth. The effect of depth on wedge factor is significant with increasing wedge filter angle. When the depth changed from 1.Scm to 10cm, wedge factor demonstrated 2.5% deviation. The fields also has significant effect on wedge factor that is improved along with the rising fields. When the field is small and the depth is little, wedge factor that is less than the standard results. Conversely, the wedge factor that is more than the standard results. Conclusion There is an error when wedge field dosage is calcalatedwith traditional methods. As quality-control requirement, the accuracy of wedge factor is not more than 2%. Detceting and using various wedge field＇s wedge factor are key to aquire accute results of dosage detecting and getting rid of error. In order to aquire the quality of radiotherapy and quality- control demanding, depth of wedge factor must be modified, wedge factor for relative depth must be taken.