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目的:应用不同仪器与方法测量加速器6 MV X线射野的特性,比较各方法的优劣和局限性,探讨快速简便检测射野特性的方法。材料与方法:分别采用电离室和半导体探头配合三维射野分析仪测量加速器6 MV X线不同射野大小的百分深度剂量曲线PDD和离轴比曲线OCR,并以二维电离室矩阵测量相同条件的OCR。(1)比较采用电离室和半导体探头测量PDD的差别。(2)比较两维矩阵与电离室半导体探头测量射野的对称性、平坦度、射野大小和半影等的差别。结果:对小于15 cm×15 cm照射野,半导体探头和电离室测量PDD的结果一致性较好,两者偏差小于1.3%。对于20 cm×20 cm照射野,半导体探头的测量结果大于电离室,最大差别3.5%,偏差为2.6%。用半导体探头与电离室测量射野的大小,两者的最大差别为0.6 mm,两者有较好的一致性,二维电离室矩阵测量与前两者比较,最大差别为2.9 mm,最小差别0.5 mm。三种方法测量的射野平坦度差别在1.2%~2.6%,矩阵的测量数值在半导体和电离室测量范围之内。结论:在检测加速器射野性能时,二维矩阵可以快速检测射野平坦度、对称性,但测量射野大小时可能有较大误差,不宜用作验收加速器和收集治疗计划系统数据的精细工作。
OBJECTIVE: To measure the characteristics of 6 MV X-ray accelerator using different instruments and methods, and to compare the advantages and disadvantages of each method and its limitations, and to explore a method for quickly and easily detecting the field characteristics. MATERIALS AND METHODS: The percent depth dose curve PDD and off-axis curve OCR of different field sizes of accelerator 6 MV X-ray were measured respectively by ionization chamber and semiconductor probe in combination with three-dimensional field analyzer, and measured in the two-dimensional ionization chamber matrix Condition of OCR. (1) Compare the differences between PDDs using ionization chambers and semiconductor probes. (2) Compare the difference of the symmetry, flatness, field size and penumbra between two-dimensional matrix and ionization chamber semiconductor probe. Results: The results of PDD measured by the semiconductor probe and ionization chamber were better than those of the irradiated field less than 15 cm × 15 cm. The deviation between them was less than 1.3%. For the 20 cm × 20 cm irradiation field, the measurement results of the semiconductor probe are larger than the ionization chamber with the maximum difference of 3.5% and the deviation of 2.6%. The maximum difference between the two measurements is 0.6 mm. The two are better agreement. The difference between two-dimensional ionization chamber matrix measurement and the former two is 2.9 mm, the minimum difference 0.5 mm. The difference between the two methods is 1.2% -2.6%. The matrix measurement values are within the measurement range of the semiconductor and the ionization chamber. Conclusions: Two-dimensional matrices can quickly detect field flatness and symmetry when detecting accelerator field performance. However, there may be large errors in measuring field size and should not be used as fine work for acceptance accelerators and collection planning data .