瓦里安千伏级锥形束CT系统间剂量学一致性研究

Dosimetric consistency of different Varian kV-cone beam CT systems:a comparative study

目的:以两台相同型号、不同机龄的瓦里安锥形束CT(CBCT)为平台,选取球管电压值kVp与加权CT剂量指数CTDI_w,分别测量验证6套标准扫描参数的系统间剂量学一致性。方法:(1)选取德国PTW管电压表验证标称电压稳定性;(2)选取德国PTWCT电离室,分别在Full-fan和Half-fan模式下测量直径为16 cm头部和32 cm体部一体式CTDI模体中心和外周4点剂量以计算CTDI_w;(3)利用SPSS 21.0版软件对数据进行检验,P<0.05为统计学有显著意义。结果:实测管电压均高于标称值,新旧CBCT的6个扫描参数平均偏高(2.5±0.7)k Vp和(2.9±0.8)kVp,相对偏差范围1.30%~3.12%;旧CBCT各参数的CTDI_w值均高于新CBCT,偏差幅度4.90%~11.46%,平均偏高8.73%±2.95%。结论:瓦里安CBCT的剂量学稳定性较好,但球管电压的偏差有随着使用年限增加的趋势,相同型号、相同扫描参数的机器间CTDI_w值也不尽相同。CBCT的剂量学一致性应该作为常规质量控制和工作保证的一部分进行监测。

Objective To verify the dosimetric consistency between two Varian CBCT systems of the same type but of different working years using 6 sets of standard scanning parameters.Methods The stability of the tube voltage（kVp） of the two systems was measured using PTW DIAVOLT-MULTI（Germany）.In a standard CTDI phantom consisting of the head and body modules（diameters of 16 cm and 32 cm,respectively）,the dose at the central and 4 peripheral points were measured with a PTWCT chamber（Germany） to calculate the weighed CT dose index（CTDIw） in both the full-fan and half-fan modes.Results Measurement using the 6 sets of standard scanning parameters showed that the k Vp of both the new and old CBCT systems was higher than the nominal values by（2.5±0.7） k Vp and（2.9±0.8） k Vp,respectively,with deviations ranging from 1.3% to 3.12%.Compared to the new system,the old CBCT system had a higher CTDIwby（8.73±2.95）% on average,with deviations ranging from 4.90% to 11.46%.Conclusion The dosimetric consistency of Varian CBCT is stable but the deviation of kVp increases as the working year of the machine increases.The CTDIwcan vary between different Varian CBCT systems even of the same type and with the same scanning parameters.Monitoring of the dosimetric consistency is recommended for routine quality control and maintenance of the CBCT systems.