临床放射治疗切线照射时气腔及空气间膈对中心轴剂量的影响

THE EFFECT OF AIR GAP AND AIR GAVITY ON SURFACE DODSE ALONG CENTRAL AXIS FOR TANGENTIAL INCIDENCE IN RADIATION THERAPY

目的口腔内肿瘤及胸部肿瘤放射治疗时，野内存在空气膈和气腔，这种结构会对治疗剂量有一定影响。本研究对放射治疗时体内气腔及空气膈对射野中心轴的剂量影响进行了研究。方法以聚丙稀酸体模模拟口腔放疗与胸部肿瘤放疗时的空气膈和气腔结构，以平板电离室测量中心轴剂量的大小。射线能量分别取Ｃｏ－６０和６ＭＶＸ线。结果对有空气膈结构组织照射时，随空气间膈的距离不同，对中心轴剂量的影响不同，对Ｃｏ－６０：在空气间隔５ＣＭ时中心轴剂量减少２５％，对６ＭＶＸ线则有３０％，对有气腔的组织，气腔的存在对中心轴的侧向剂量贡献减小２％以上。结论在有气膈的组织放疗时必须考虑气膈对中心轴上剂量的影响。而对有气腔组织放疗时，气腔的存在对中心轴上剂量的贡献可以忽略。

Objective To study the effect of air gap and air cavity on surface dose along central axis (SDACA) if there exists air gap or air cavity in the radiation field when treating oral tumor or chest tumor with radiation therapy. Method Surface dose of Co-60 and 6MVX along central axis was measured by using plate ionization chamber in air gap or air cavity structure simulated by acrylic phantom. Result When iiradiating the air gap structure, the effect of air gap on SDACA changed. To Co-60, SDACA reduced 25% when air gap was 5cm; to 6MVX, surface dose reduced 30%. It reduced only 2% when there existed air cavity. Conclusion The effect of air gap on SDACA should be considered when radiating tissue with air gap while the effect of air cavity on SDACA should'n be considered when radiating tissue with air cavity.