高能X射线下水等效材料对水的等效性研究

Study on the Equivalence of Water Equivalent Materials to Water under High-energy X-ray

针对水等效材料校准医用加速器中存在的问题,通过对比法测量水体模和3种水等效材料校准医用加速器的剂量学差异,分别给出PTW 30013和IBA FC65-G两种类型探测器在校准深度为5 cm和10 cm的修正因子。针对加速器日稳定性校准的必要性,通过近7个月的日稳定性测量结果,给出加速器漂移量和引起漂移的可能原因;针对水等效材料在相对测量中对水的等效性,通过测量12个辐射野的输出因子,得出水等效材料在相对测量中与水一致。最后给出水等效材料在高能X射线下水吸收剂量校准时的建议和注意事项。

The problems in the calibration of accelerator using water equivalent materials were described. Three commonly used water equivalent materials were compared to water phantom in measurements of absorbed dose to water. Two Farmer-type cylindrical chamber,PTW 30013 and IBA FC65-G,were used in measurements. The calibration factors of absolute dose between water phantom and water equivalent materials at two depth,5 cm and 10 cm,were listed. Through the results of daily stability nearly seven months,the necessity of daily calibration of the accelerator was explained. The dose drift of accelerator and the possible causes were given. By measuring the output factor of twelve radiation fields,the water equivalent material is consistent with water in the relative measurement. Finally,the suggestions and precautions for the water equivalent material in the calibration of high energy X-ray were given.