电子束环形限光筒剂量学特性的测量

Dosimetric Characteristics of Electron Circular Applicators

目的:研究一种新型不锈钢壁环形限光筒的剂量学特性。方法:用PTWmp3三维水箱在标称源皮距下测量环形限光筒的百分深度剂量和照射野离轴比,用PTWUNIODS剂量仪和0.6cc电离室测量射野输出因子、有效源皮距和X线污染,并将测量结果与6cm×6cm限光筒中制作的相同孔径的圆形铅块做比较。结果:环形限光筒电子线照射野的百分深度剂量、离轴比和有效源皮距与电子束能量、限光筒型号密切相关。有效射程和治疗深度随限光筒孔径增大而增大。限光筒直径越小,电子线能量越大,表面剂量越高。环形限光筒的输出因子和相同孔径的圆形铅块不同,随能量变化较大。X线污染比较小。结论:环形限光筒的剂量学特性能满足临床要求,对于小肿瘤具有很好的适形效果,适合表浅的淋巴结预防照射、口腔粘膜肿瘤和某些管腔肿瘤治疗,也可以用于术中照射。

Objective： To study the dosimetric characteristics of new stainless wall circular cones provided with Synergy accelerator. Methods： Percentage depth doses （PDD） and beam profiles were scanned using PTW mp3 water phantom under normal source-to-skin distance （SSD）. Cone output factors, effective source-to-surface distances and X-ray contaminations were evaluated by point dose measurement using Unidos electrometer and 0.6 cc ion chamber. The measurement results were compared to that of the circular field inserts in a 6 cm×6 cm applicator. Results： The PDDs, beam profiles, effective SSDs, and X-ray contaminations were dependent on the electron beam energy and cone size. For the same beam energy, the practical range and the tumor depth increased with the cone size. Higher surface doses were found with the higher beam energy and smaller cone. The cone output factors changed with the beam energy, and were quite different from that of the inserts. The X-ray contaminations were very small. Conclusion： Dosimetric parameters of circular cones can meet the clinical situations. Due to its conformal field shaping to small tumors, the circular cones can be conveniently used to deliver doses to lympha node, tumor inside a cavity, or in electron operative irradiation.