利用百分深度剂量计算组织最大剂量比的准确性研究

Accuracy of Derivation of Tissue Maximum Ratios From Measured Percentage Depth Doses

目的:研究用测量的X线照射野百分深度剂量和体模散射输出因子计算组织最大剂量比的可行性。方法:用PTWmp3三维水箱分别测量Precise加速器的6 MV和10 MVX线的百分深度剂量、组织最大剂量比以及照射野输出因子。利用NE2570剂量仪和自制的圆柱形有机玻璃体模测量加速器准直系统散射输出因子。用Visual Basic 6.0编程计算组织最大剂量比,并将组织最大剂量比的计算值和测量值进行比较。结果:组织最大剂量比和射线能量、照射野面积有关。6 MV和10 MVX线的组织最大剂量比的计算值和测量值的误差小于2%。结论:组织最大剂量比的计算值和测量值符合得很好,可以直接应用于吸收剂量计算。

Objective： To evaluate the feasibility of calculation of tissue maximum ratios from measured percentage depth doses and phantom scatter output factors. Methods： Percentage depth doses, tissue maximum ratios and output factors are measured for Precise 6 MV and 10 MVX-rays respectively in PTW mp3 water phantom. Collimator output factors are measured using self-made small cylindrical perspex phantoms and NE 2570 ion chamber. TMR was calculated through an in-home code in Visual basic 6.0, and compared with the measured values. Results： Tissue maximum ratios varied with the beam energy and field size. The calculated and measured TMRs for 6 MV and 10 MVX-rays are within ±2%. Conclusions： The calculated TMRs can be used in accurate dose calculation.