基于TRS-483报告的小野输出因子测量与验证研究

Small Field Output Factor Measurement and Verification Based on TRS-483

为测量小野输出因子,采用国际原子能机构(IAEA)出版的TRS-483报告方法,测量了Elekta Synergy直线加速器标称6 MV、10 MV辐射场的组织模体比(TPR_(20,10)(10)),6 MV、10 MV能量TPR_(20,10)(10)分别为0.683和0.735。通过计算电离室适用的最小半高宽验证了多种电离室可测射野范围,选用的电离室可测最小半高宽在3~4 cm之间。对探测器灵敏体积、测量剂量和剂量率线性、漏电流、重复性和稳定性进行比较,选择了18种不同型号共21支探测器,在加速器TPR_(20,10)(10)为0.683和0.735的辐射场,源皮距(SSD)分别为90 cm和100 cm的条件下计算1 cm×1 cm,2 cm×2 cm,3 cm×3 cm,4 cm×4 cm,5 cm×5 cm和8 cm×8 cm方野与10 cm×10 cm方野的探测器电荷比值得到未修正的射野输出因子,乘以TRS-483报告的修正系数后得到修正射野输出因子,修正后的射野输出因子与平均值最大差异小于2.5%。结果表明:使用TRS-483报告的修正因子可提高不同探测器测量小野剂量的一致性。

To measure small field output factor,the tissue-phantom ratio(TPR_(20,10)(10))of the Elekta Synergy linear accelerator nominal radiation energy of 6 MV and 10 MV were measured using TRS-483 report method published by IAEA,which were 0.683 and 0.735.By calculating the minimum FWHM applicable to the ionization chamber,various measurable radiation field ranges of the ionization chamber were verified.The FWHM of the selected ionization chambers are between 3~4 cm.By comparing the sensitive volume,linearity of measured dose and dose rate,leakage current,repeatability and stability,a total of 21 detectors from 18 different models were selected.Under the condition of TPR_(20,10)(10)=0.683,0.735,source skin distance(SSD)of 90 cm and 100 cm,1 cm×1 cm,2 cm×2 cm,3 cm×3 cm,4 cm×4 cm,5 cm×5 cm and 8 cm×8 cm square field to 10 cm×10 cm square field output factors were measured and multiplied by the correction factor reported by TRS-483.The maximum difference between the corrected radiation field output factor and the mean value is less than 0.025.The results show that using the correction factor reported by TRS-483 can improve the consistency of measurement of small field dose by different detectors.