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[目的]了解用深部X线治疗时 ,限光筒端面与体表之间空隙造成的体表剂量变化。[方法]用半导体电离室和热释光剂量仪测出不同射线质、射野尺寸、源皮距(SSD),以及斜入射存在条件下 ,间隙从1mm～15mm变化时体表剂量改变情况。并用三维水箱扫描出PDD的变化。[结果]取得了不同因素影响下剂量改变情况的数据 ,并分析了以上因素对剂量改变的影响。[结论]当间隙从1mm～15mm变化时 ,体表欠剂量最大可达12 %左右 ,射野尺寸 ,射线质对剂量变化有一定影响 ,SSD的影响可忽略 ,当间隙和斜入射同时存在时 ,欠剂量情况有所改善。小空隙对PDD影响可忽略。
[Objective] To understand the changes of body surface dose caused by the gap between the end face of the light-limiting tube and the body surface during deep X-ray treatment. [Method] With the ionization chamber and thermoluminescence dosimetry, the dose changes of body surface were measured when the gap changed from 1mm to 15mm with different radiance, field size, source distance (SSD) and oblique incidence. And use the 3D water tank to scan the PDD changes. [Result] The data of dose change under different factors were obtained, and the influence of the above factors on the dose change was analyzed. [Conclusion] When the gap varies from 1mm to 15mm, the dose under the body surface can reach a maximum of about 12%. The radiation field size and radiation quality have some effects on the dose variation. The influence of SSD is negligible. When the gap and oblique incidence exist simultaneously , The under-dose situation has improved. Small gaps have negligible effect on PDD.