Jursinic P A, Mackie T R
Medical Physics Department, University of Wisconsin, Madison 53706, USA.
Phys Med Biol. 1996 Aug;41(8):1499-509. doi: 10.1088/0031-9155/41/8/016.
Megavoltage x-ray beams generated by linear accelerators (linacs) deliver their maximum dose a few centimetres below the treatment or phantom surface. This skin-sparing effect is degraded by the generation of secondary electrons as the x-ray beam passes to the patient or phantom. This work measures the characteristics of these electrons. A light-weight electromagnet was constructed that could be mounted in the block-tray position, 58 cm from the x-ray source of a Varian Clinac 2100C or 2500 linac. A field strength as high as 0.1500 T was generated, which was strong enough to sweep secondary electrons out of a 10 cm x 10 cm field. For 6, 10 and 24 MV x-ray beams, secondary contamination electrons produced 18, 38 and 65% of the surface dose, corresponding to 3, 5 and 12% of the maximum dose, respectively. A parameterized depth-dose curve for the contamination electrons was produced and was valid for all the x-ray energies studied.
直线加速器产生的兆伏级X射线束在治疗表面或模体表面下方几厘米处达到其最大剂量。当X射线束穿过患者或模体时，二次电子的产生会降低这种皮肤保护效应。这项工作测量了这些电子的特性。构建了一个轻质电磁铁，它可以安装在距Varian Clinac 2100C或2500直线加速器的X射线源58厘米处的挡块托盘位置。产生了高达0.1500 T的场强，该场强足以将二次电子扫出10 cm×10 cm的射野。对于6、10和24 MV的X射线束，二次污染电子分别产生了表面剂量的18%、38%和65%，分别对应最大剂量的3%、5%和12%。生成了污染电子的参数化深度剂量曲线，该曲线对所有研究的X射线能量均有效。
