不同照射条件下6MV X线对皮肤剂量的影响

目的:通过比较研究不同临床照射条件下,6 MV X线对皮肤剂量的影响。方法:在常规治疗模式下,利用平行板电离室在固体水中测量不同射野大小、不同源皮距(SSD)、(有/无)有机玻璃挡铅托板、动态楔形板、固定楔形板、多叶准直器(MLC)及低熔点合金挡铅等不同照射参数条件下皮肤相对受量。结果:皮肤剂量随着照射野由3 cm×3 cm到30 cm×30 cm时,其剂量由8%上升到30%;皮肤剂量随源皮距(SSD)的增加而逐渐降低,并且这种变化在大野时比较明显;有机玻璃挡铅托板的使用明显增加了皮肤受量且在大野时增加更为显著;在使用固定楔形板时(各角度),皮肤剂量较开野小,然而在使用动态楔形板时,皮肤剂量因楔角不同而不同,在小角度时皮肤受量与开野相似,但在大角度时,皮肤受量有较明显的降低;低熔点合金挡铅增加了皮肤剂量,MLC对皮肤剂量的影响类似低熔点合金挡铅,但增加效果没有合金挡铅明显。结论:在不同的照射条件下,皮肤的受量有较大的变化,因此本研究的意义在于揭示这种影响,为以后治疗计划设计提供参考意见。

Skin Dose Analyses For Various Beam Modifiers From Linear Accelerator Produced 6 MV Photon

Objective：To learn the skin dose for different clinical setups for 6 MV photon.Methods：The surface doses were measured using a parallel-plate chamber under conditions relevant to routine radiotherapy treatments.The measurements include： the effect of field size,Source-to-Surface distance（SSD）,acrylic block tray,dynamic wedges and fix wedges,multileaf collimator（MLC）,and cerrobend block.Results：The skin dose increased as field size increased.When the fields from 3 cm×3 cm to 30 cm×30 cm,the skin dose raise from 8% to 30%;As SSD increase,the skin dose decrease,and this effect was dominant in large field;Due to the use of an acrylic block tray the surface dose was increased for all field size and the percentage skin dose was more dominant at larger field size.When the fix wedge was used,the skin doses were lower than open fields.As for dynamic wedge,the skin doses various as the angel of the wedge.The effect of a low angle wedge on skin dose was very similar to open field,but for high angle wedge.Field-shaping block increased the skin dose.The effect of an MLC on skin dose was very similar to that of metal block,but its magnitude was less.Conclusion： The skin dose has great various in different clinical setups.Therefore,the significance of this study is to reveal the effects of the treatment plan for the future design reference.