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目的：按 Sp的定义，直接测量体模散射因子 Sp。方法：在准直器开口不变的情况下，用加挡块的方法改变各射野在模体中的散射面积。分别测定各射野在模体中参考点处的吸收剂量率和加挡块后同一点的吸收剂量率，再根据 Sp的定义，计算出 Sp因子。结果：通过测量，直接得到各射野的体模散射因子 Sp和总散射校正因子 Scp，然后求出各射野的准直器散射修正因子 Sc。结论：用本文加挡块的方法测定 Sp因子，可以降低制作高能 X线的平衡帽的要求，而且也可避免平衡帽有限体积带来 Sc的测量误差。
Objective: According to the definition of Sp, direct measurement of phantom scattering factor Sp. Methods: With the collimator opening unchanged, the area of scattering of each field in the phantom was changed by adding a stopper. The radiation dose rate at the reference point and the dose rate at the same point after the block were measured respectively. The Sp factor was calculated according to the definition of Sp. Results: The phantom scatter factor Sp and total scatter correction factor Scp of each field were directly obtained by measurement, and then the collimator scattering correction factor Sc of each field was obtained. Conclusion: The Sp-factor method can be used to reduce the need for a high-energy X-ray balance cap and to avoid the measurement error of Sc from the limited volume of the balance cap.