Arun C, Palani Selvam T, Dinkar Verma, Munshi Prabhat, Kalra Manjit Singh
Department of Radiotherapy, M N B Cancer Institute Inlaks and Budhrani Hospitals, Pune 411 001, India.
Radiol Phys Technol. 2013 Jan;6(1):151-6. doi: 10.1007/s12194-012-0181-2. Epub 2012 Nov 20.
This study presents Monte Carlo-calculated absolute and normalized (relative to a (60)Co beam) sensitivity values of silicon diode dosimeters for a variety of commercially available silicon diode dosimeters for radiotherapy photon beams in the energy range of (60)Co-24 MV. These values were obtained at 5 cm depth along the central axis of a water-equivalent phantom of 10 cm × 10 cm field size. The Monte Carlo calculations were based on the EGSnrc code system. The diode dosimeters considered in the calculations have different buildup materials such as aluminum, brass, copper, and stainless steel + epoxy. The calculated normalized sensitivity values of the diode dosimeters were then compared to previously published measured values for photon beams at (60)Co-20 MV. The comparison showed reasonable agreement for some diode dosimeters and deviations of 5-17 % (17 % for the 3.4 mm brass buildup case for a 10 MV beam) for some diode dosimeters. Larger deviations of the measurements reflect that these models of the diode dosimeter were too simple. The effect of wall materials on the absorbed dose to the diode was studied and the results are presented. Spencer-Attix and Bragg-Gray stopping power ratios (SPRs) of water-to-diode were calculated at 5 cm depth in water. The Bragg-Gray SPRs of water-to-diode compare well with Spencer-Attix SPRs for ∆ = 100 keV and above at all beam qualities.
本研究给出了通过蒙特卡罗计算得到的，能量范围在钴 - 60至24兆伏的放射治疗光子束所用的多种市售硅二极管剂量计的绝对灵敏度值和归一化（相对于钴 - 60束）灵敏度值。这些值是在10厘米×10厘米射野尺寸的水等效体模中心轴上5厘米深度处获得的。蒙特卡罗计算基于EGSnrc代码系统。计算中考虑的二极管剂量计具有不同的建成材料，如铝、黄铜、铜以及不锈钢 + 环氧树脂。然后将计算得到的二极管剂量计归一化灵敏度值与先前发表的钴 - 60至20兆伏光子束的测量值进行比较。比较结果显示，对于一些二极管剂量计有合理的一致性，而对于一些二极管剂量计存在5% - 17%的偏差（对于10兆伏束，3.4毫米黄铜建成情况偏差为17%）。测量中较大的偏差反映出这些二极管剂量计模型过于简单。研究了壁材料对二极管吸收剂量的影响并给出了结果。在水中5厘米深度处计算了水与二极管的斯宾塞 - 阿蒂克斯和布拉格 - 格雷阻止本领比（SPRs）。在所有射束品质下，对于∆ = 100千电子伏及以上，水与二极管的布拉格 - 格雷SPRs与斯宾塞 - 阿蒂克斯SPRs比较吻合。
