Varatharaj C, Ravikumar M, Sathiyan S, Supe Sanjay S
Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore, India.
J Med Phys. 2011 Jul;36(3):133-7. doi: 10.4103/0971-6203.83475.
The use of megavoltage X-ray sources of radiation, with their skin-sparing qualities in radiation therapy, has been proved useful in relieving patient discomfort and allowing higher tumor doses to be given with fewer restrictions due to radiation effects in the skin. The purpose of this study was to compare the dosimetric characteristics of a physical and enhanced dynamic wedge from a dual-energy (6 and 18 MV) linear accelerator such as surfaces doses with different source to surface distances (SSD), half value layer (HVL) in water and peripheral doses for both available energies. At short SSD such as 85 cm, higher surface doses are produced by the lower wedges by the short wedge-to-skin distance. For physical wedged field, at heel edge side HVL value was high (17 cm) compared with the measured that of EDW (15.1 cm). It was noticed that, the HVL variation across the beam was significantly higher for 6 MV X-rays than for 18 MV X-rays. The lower wedge has the maximum variation of peripheral dose compared to other wedges. The three wedge systems discussed in this work possess vastly different dosimetric characteristics. These differences will have a direct impact on the choice of the wedge system to be used for a particular treatment. Complete knowledge of the dosimetric characterisitics, including the surface and peripheral doses, is crucial in proper choice of particular wedge systems in clinical use.
兆伏级X射线辐射源在放射治疗中具有皮肤 sparing特性，已被证明有助于减轻患者不适，并允许在较少受到皮肤辐射效应限制的情况下给予更高的肿瘤剂量。本研究的目的是比较双能（6和18兆伏）直线加速器的物理楔形和增强动态楔形的剂量学特性，如不同源皮距（SSD）下的表面剂量、水中半价层（HVL）以及两种可用能量下的周边剂量。在短SSD（如85厘米）时，较低的楔形由于楔形到皮肤的距离短而产生较高的表面剂量。对于物理楔形野，足跟边缘侧的HVL值较高（17厘米），而与测量的增强动态楔形（EDW）的HVL值（15.1厘米）相比。值得注意的是，6兆伏X射线的束流中HVL变化比18兆伏X射线的显著更高。与其他楔形相比，较低的楔形周边剂量变化最大。本研究中讨论的三种楔形系统具有截然不同的剂量学特性。这些差异将直接影响用于特定治疗的楔形系统的选择。全面了解剂量学特性，包括表面和周边剂量，对于临床使用中正确选择特定的楔形系统至关重要。
