X射线容积成像图像引导系统所致病人吸收剂量的测量方法研究

Study on measurement method of patient absorbed dose caused by XVI imaging system

目的:探讨一种基于TG-61号报告,利用Farmer型电离室和自制圆柱形水模体对医科达X射线容积成像(X-ray volumetric imager,XVI)(Elekta,Sweden)图像引导系统所致病人吸收剂量进行测量的方法。方法:将电离室和剂量仪送检中国计量科学研究院获得针对kV级X射线不同管电压和半价层条件下电离室的照射量修正因子N_(X)并转换成空气比释动能修正因子N_(K),测量出本科室所用XVI系统在不同kVp工作条件下的X射线半价层,利用自制的两种圆柱形水模体对不同扫描预案条件下XVI系统图像引导过程所致病人吸收剂量进行测量。结果:XVI系统100 kV及120 kV两种能量射线的半价层分别为6.00 mm-AL及6.95 mm-AL。头颈和盆腔两种扫描预案的锥形束CT权重剂量指数(weighted-cone-beam computed tomography dose index,CBCTDIw)分别为1.2 mGy和40 mGy。结论:虽然基于TG-61报告的测量方法很难准确获得P_(Q,cham)和[(μ_(en)/ρ)_(air)^(w)]_(water)两个参数,但总体测量精度相对较高,测量方法简单直接,是测量千伏级锥形束CT(kV cone-beam computed tomography,kV-CBCT)图像引导过程所致病人吸收剂量的理想办法。

Objective:To investigate a method of measuring the absorbed dose of XVI imaging system using Farmer type ionization chamber and self-made cylindrical water phantom,based on AAPM TG-61 report.Methods:Obtained the exposure correction factors of chamber and electrometer from China National Institute of Metrology for different beam qualities of kV X-ray.Then converted them into air kerma correction factors.Measured the half-value-layers(HVLs)of XVI imaging system for different kVps,and then measured the absorbed dose of XVI imaging system for different protocols with two self-made cylindrical water phantoms.Results:The HVLs of 100 kV and 120 kV of XVI system were 6.00 mm-AL and 6.95 mm-AL,respectively.Weighted-cone-beam computed tomography dose index(CBCTDIw)of head-and-neck and pelvic protocols were 1.2 mGy and 40 mGy,respectively.Conclusion:Although it is hard to obtain P_(Q,cham) and [(μ_(en)/ρ)_(air)^(w)]_(water)precisely,the method we investigated is relatively accurate and intuitive,it is an ideal method to study the imaging dose of kV-CBCT system.