The study effects of the material of buildup cap to the measured value of output factor / 中国医学物理学杂志

ABSTRACT

To study the effects of the material of a buildup cap to the determined value of Output FactorSc．Material and MethodsUsing two buildup caps made of plastic A－150 and copper respectively．The ionizing values of ionization chamber were measured with Farmer 2570 electrometer in the fields of all kinds of sizes respectively and calibrated to reference field．Two groups of values of Sc were obtained and compared． Results The ionizing values measured with the buildup cap of copper is evidently larger than with the buildup cap of plastic A－150 and the maximum is 14％ but the difference between two groups of the values of Sc is not much evident and all is in the range of 1％． Conclusions Though the material of high density is not equivalent with airthe effects of that to the measured value of Sc is less．So using the buildup cap made of the material of high density for the measurement of Sc is also a quite good method specially in the fields of the small sizes．