McParland B J
Division of Radiation Physics, Cancer Control Agency of British Columbia, Victoria Cancer Clinic, Canada.
Med Phys. 1991 Jul-Aug;18(4):740-3. doi: 10.1118/1.596733.
In a number of clinical situations, the dose to the skin and the superficial tissues is of concern. Both beam obliquity and a beam modifier will modify the dose delivered to these regions due to changes in the scattering geometry, scattered photon and secondary electron production, and changes in the energy spectrum of a polyenergetic beam. Some linear accelerators use a single universal wedge mounted within the treatment head. Because such a wedge is at an extended distance from the patient, its contribution to the beam contaminants incident to the skin will be limited. Measurements of the ionization in the buildup region have been performed in a polystyrene phantom irradiated with a 6-MV x-ray beam from a linear accelerator equipped with a universal wedge. The variation of the buildup dose with obliquity, universal wedging, and distance from the source has been measured for angles of incidence between 0 degrees and 60 degrees and for effective wedge angles between 0 degrees and 45 degrees. The results indicate that the percentage buildup has a much stronger dependence upon the angle of incidence than upon the effective wedge angle. For distances approaching the treatment head, it is shown that the universal wedge generates secondary electrons that elevate the surface dose, but that this contribution decreases with distance.
在许多临床情况下，皮肤和浅表组织所接受的剂量备受关注。由于散射几何形状、散射光子和二次电子产生的变化以及多能束能谱的变化，射束倾斜度和射束修正器都会改变传递到这些区域的剂量。一些直线加速器在治疗头内使用单个通用楔形板。由于这种楔形板离患者有一段距离，它对入射到皮肤的射束污染物的影响将是有限的。在配备通用楔形板的直线加速器产生的6兆伏X射线束照射的聚苯乙烯体模中，对建成区的电离进行了测量。已测量了入射角在0度至60度之间以及有效楔形角在0度至45度之间时，建成剂量随倾斜度、通用楔形板和源距离的变化。结果表明，建成剂量百分比对入射角的依赖性比对有效楔形角的依赖性要强得多。对于接近治疗头的距离，结果表明通用楔形板会产生二次电子，从而提高表面剂量，但这种影响会随着距离的增加而减小。
