Wang D, Sobolewski M, Hill R
Institute of Medical Physics, University of Sydney, Sydney, Australia.
Australas Phys Eng Sci Med. 2012 Dec;35(4):491-5. doi: 10.1007/s13246-012-0166-9. Epub 2012 Nov 29.
The objective of this work was to evaluate the dosimetry of tungsten eye shields for use with kilovoltage X-ray beam treatments. The eye shields, originally designed for megavoltage electron beams, were made of 2 mm tungsten thickness and inside diameters of 11.6 and 15.0 mm with optional aluminium caps of 0.5 and 1 mm thickness. The relative dosimetry of the eye shields were examined by measurement of transmission doses with full scatter conditions, central axis depth doses and beam profiles underneath the eye shield. The X-ray beams used in this study ranged in energy from 50 to 280 kVp. Transmission measurements were performed using an Advanced Markus ionisation chamber located at the surface of an RMI457 Solid Water phantom with a 3 cm diameter applicator flush against the phantom surface. Depth doses and profiles measurements were performed in a PTW MP3 scanning water tank with a PTW diamond detector. Results for transmission doses for the medium size eye shield increased from 1 to 22 % for 50-280 kVp while for the smaller eye shield the percentage dose increased from 3.5 to 30 % for the same energy range. There were minimal differences between using the 0.5 and 1 mm aluminium caps. Central axis depth doses measured with and without the eye shields demonstrated the 125 and 180 kVp beams had higher peak doses behind the eye shields. These results show that these tungsten eye shields are suitable for use with kilovoltage X-ray beams. However, the clinical impact needs to be considered for the higher X-ray beam energies.
这项工作的目的是评估用于千伏级X射线束治疗的钨制眼罩的剂量测定。这些眼罩最初是为兆伏级电子束设计的，由2毫米厚的钨制成，内径分别为11.6毫米和15.0毫米，并配有厚度为0.5毫米和1毫米的可选铝帽。通过在全散射条件下测量透射剂量、中心轴深度剂量以及眼罩下方的射野轮廓来检查眼罩的相对剂量测定。本研究中使用的X射线束能量范围为50至280 kVp。透射测量使用一个先进的马库斯电离室进行，该电离室位于RMI457固体水模体表面，直径3厘米的施源器与模体表面齐平。深度剂量和轮廓测量在配有PTW钻石探测器的PTW MP3扫描水箱中进行。对于中等尺寸的眼罩，50 - 280 kVp时透射剂量结果从1%增加到22%，而对于较小尺寸的眼罩，在相同能量范围内剂量百分比从3.5%增加到30%。使用0.5毫米和1毫米铝帽之间的差异极小。在有和没有眼罩的情况下测量的中心轴深度剂量表明，125 kVp和180 kVp的射线束在眼罩后方具有更高的峰值剂量。这些结果表明，这些钨制眼罩适用于千伏级X射线束。然而，对于较高能量的X射线束，需要考虑其临床影响。
