The dependency of the output factor on the field size in the passive scattering proton therapy at the National Cancer Center (NCC) in Korea was investigated through a comparison of the measured output factors. The output factor of the fields of the representative beam options was measured using a Pinpoint chamber with standard circular blocks of less than 5 cm in diameter. The measured output factors for different field sizes show that the dependency of the output factor on the field size is not negligible even in the field for the 5 cm in diameter for long-range proton beams. In addition, the conflicting dependency in shallow fields indicates that the potential contribution of scattered protons should be considered in predicting and modelling of the output factors in small fields.

中文翻译：

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韩国国立癌症中心被动散射质子治疗中输出因子对场大小依赖性的调查

通过比较测量的输出因子，研究了韩国国家癌症中心 (NCC) 被动散射质子治疗中输出因子对场大小的依赖性。使用具有直径小于 5 cm 的标准圆形块的 Pinpoint 室测量代表性光束选项的场的输出因子。不同场尺寸的测量输出因子表明，即使在长距离质子束直径为 5 cm 的场中，输出因子对场尺寸的依赖性也不容忽视。此外，浅场中相互矛盾的依赖性表明，在小场中的输出因素的预测和建模中应考虑散射质子的潜在贡献。