两种固体模体水等效特性的比较研究

Dosimetric characteristics of water equivalent for two solid water phantoms

目的对两种固体模体的水等效性及相关校准因子进行检测。方法对美国MED—TEC公司虚拟水和德国PTW公司RW3两种固体模体不同深度处进行X线、电子线照射测量，得到深度电离量曲线与水模体中的进行比较，而水等效因子两种模体直接比较。按照国际原子能机构定义得到不同能量电子线深度比例因子（Cpl）与注量比例因子（hpl），比较两种模体间差异。结果两种固体模体与水模体的深度电离量平均偏差在6MVX线时为0．42％和0．16％（t=-6．15，P=0．001和t=-1．65，P=0．419），10MVX线时为0．21％和0．31％（t=1．73，P：0．135和t=2．30，P=0．061），6MeV电子线时为17．4％和14．5％（t=-1．37，P=0．208和t=-1．47，P=0．179），15MeV电了线时为7．0％和6．0％（t=-0．58，P=0．581和t=-0．90，P=0．395）。两模体水等效因子变化均较大，但在参考测量点附近接近1，在6MVX线时F=58．54、P=0．000，10MVX线时F=0．21、P=0．662，6MeV电子线时F=0．97、P=0．353，15MeV电子线时F=0．14、P=0．717。随着电子线能量增加Cpl值增加（F=26．40，P=0．014）而hpl值减少（F=7．45，P=0．072）。结论若假设固体体模为完牟=水等效则会引入系统误差，因而在临床应用中要慎重。

Objective To investigate the water equivalent of two solid water phantoms. Methods The X-ray and electron beam depth-ion curves were measured in water and two solid water phantoms, RW3 and Virtual Water. The water-equivalency correction factors for the two solid water phantoms were compared. We measured and calculated the range scaling taetors and the fluence correction factors for the two solid water phantoms in the case of electron beams. Results The average difference between the measured ionization in solid water phantoms and water was 0. 42% and 0. 16%o on 6 MV X-ray （ t = - 6. 15,P = 0. 001 and t= -1.65,P=0.419） and 0.21% and 0.31%o on 10 MV X-ray （t= 1.728,P=0.135 and t= -2.296,P=0.061）, with 17.4% and 14. 5% on 6 MeV electron beams （t= -1.37,P=0.208 andt= -1.47,P=0.179） and 7.0% and 6.0% on 15 MeV electron beams （t= -0.58,P=0.581 and t= -0. 90,P = 0. 395 ）. The water-equivalency correction factors for the two solid water phantoms varied slightly largely, F = 58.54,P = 0. 000 on 6 MV X-ray, F = 0. 211 ,P = 0. 662 on 10 MV X-ray, F = 0. 97, P =0. 353 on 6 MeV electron beams, F =0. 14,P =0. 717 on 15 MeV electron beams. However, they were almost equal to 1 near the reference depths. The two solid water phantoms showed a similar tread of Cpl increasing （ F = 26.40, P = 0. 014） and h,l decreasing （ F = 7.45, P = 0. 072 ） with increasing energy. Conclusion The solid water phantom should undergo a quality control test before being clinical use.