用二维电离室矩阵验证射野

Field Verification in Radiotherapy with Two-Dimension Ion Chamber Rrray

目的探讨用二维电离室矩阵测量射野大小与灯光标称射野大小的一致性。方法使用IBA公司的MatriXX二维电离室矩阵对VARIAN公司的23EX加速器的射野进行验证。把电离室矩阵水平放置在加速器床面上,电离室矩阵中心处于等中心位置,SAD=100cm。射野大小从4.0cm×4.0cm渐变到16cm×16cm。选用6MV-X射线,每射野出束50MU,记录测量结果。用OmniProI’mRT(1.5)软件分析测量数据,得到射野的实测大小。结果实测射野边长与标称的射野边长之差在X方向和Y方向上都随射野增大而时大(波峰)时小(波谷),呈现出明显的变化周期性。平均相邻波峰波谷间距=(7.6±0.7)mm,平均X波峰波谷高度差=(3.3±0.6)mm,平均Y波峰波谷高度差=(3.3±0.5)mm。结论在电离室矩阵中,电离室的离散性周期分布可导致实测射野大小与标称射野大小之差周期性地增大减小,用二维电离室矩阵验证射野大小时应充分考虑电离室矩阵中电离室的离散性分布所产生的影响。

Objective To research on consistency verification of radiation field size based on 2D ion chamber array matrix. Methods We have used a 2D ion chamber array detector （ IBA MatriXX） to measure the fields of VARIAN 23EX accelerator. The matrix was lied horizontally on the accelerator couch. The centre of matrix coincided with the accelerator isocen tre,SAD = 100cm. The field size was changed from 4.0cm×4.0cm to 16.4cm × 16.4cm. Irradiating 6MV - X ray 50 MU per field, the measure data was recorded , and was analysed with the sofware, OmniPRO I＇ mRT（ 1.5 ）. Results The difference between the length （X, Y） of light and radiation field displays wave mode cyclicity change with the accretion of light field length. The average distance between the border difference wave crest and trough equals （7.6 ± 0.7 ） mm. The average distance from the trough to the crest in X direction is （3.3 ± 0.6） mm, and the average distance from the trough to the crest in Y direction is （3.3± 0.5） mm. Conclusion Because the distribution of ion chamber in arrary is discrete and regulative, the difference between the length of light and radiation field displays wave mode cyclicity change with the accretion of light field length. Verifying consistency of radiation field size, the impact of discrete distribution of ion chamber in arrary over measurement result should be considered sufficiently.