Nicopoulou-Karayianni K, Koligliatis T, Donta-Bakogianni C, Karayiannis A, Litsas J
Department of Oral Diagnosis, Dental School, University of Athens, Greece.
Dentomaxillofac Radiol. 2003 Sep;32(5):327-32. doi: 10.1259/dmfr/29945418.
The aim of this study was to estimate the radiation absorbed dose at cortical tissue-implant interfaces in diagnostic radiology.
Since our interest was the radiation dose at an interface (cortical bone-implant interface), a Monte Carlo simulation was considered to be the most suitable method for studying the problem. The Monte Carlo code employed was MCNP4B. A phantom consisting of soft tissue, cortical bone, an implant and air, with appropriate chemical compositions and densities, was described in the code. The implant simulated had a commercial name of ASTM67, grade 2 and was 1.9 mm wide. The incident photon beam was divergent of 20 cm x 20 cm at a source-to-phantom distance of 40 cm. Two energy spectra were employed (70 kVp and 100 kVp, 0.5 mm Al internal filtration) and their photon fluence distribution against energy was described in the code with an energy interval of 5 keV. The computations that led to radiation dose calculations had a spatial resolution of 0.01 cm (100 microm) to allow a detailed radiation dose distribution across the cortical bone-titanium interface. Monte Carlo runs took place both with and without an implant in the phantom and, in each case, 120 million photon histories were followed, leading to a radiation dose statistical fluctuation between 5% and 10%.
The ratio of radiation dose with implant to dose without implant against depth allows a direct estimate of the effect of the implant on the radiation dose to the cortical bone surrounding the implant. At a distance >or=100 microm there was no radiation dose increase due to the titanium implant. However, in contact with the implant (i.e. the first layers of cells) there was a sharp radiation dose increase as high as 3.5 times the radiation dose compared with when the implant was absent. Also, the newly formed bone inside the implant's tiny hole received a radiation dose close to 50% of the radiation dose without the implant owing to high absorption by the implant itself.
Assuming that the patient received five radiographic images over a 6-month period, the maximum radiation dose at the cortical bone-titanium interface was estimated to be less than 20 mGy (0.02 Gy).
本研究的目的是估算诊断放射学中皮质组织-植入物界面处的辐射吸收剂量。
由于我们关注的是界面（皮质骨-植入物界面）处的辐射剂量，蒙特卡罗模拟被认为是研究该问题最合适的方法。所使用的蒙特卡罗代码是MCNP4B。在代码中描述了一个由软组织、皮质骨、植入物和空气组成的体模，其具有适当的化学成分和密度。模拟的植入物商品名为ASTM67，2级，宽1.9毫米。入射光子束在源到体模距离为40厘米时发散为20厘米×20厘米。采用了两种能谱（70 kVp和100 kVp，0.5毫米铝内过滤），并且在代码中以5 keV的能量间隔描述了它们的光子注量随能量的分布。导致辐射剂量计算的计算具有0.01厘米（100微米）的空间分辨率，以允许详细了解皮质骨-钛界面处的辐射剂量分布。在体模中有植入物和没有植入物的情况下都进行了蒙特卡罗运行，并且在每种情况下，跟踪了1.2亿个光子历史，导致辐射剂量统计波动在5%至10%之间。
有植入物时的辐射剂量与无植入物时的辐射剂量之比随深度变化，可直接估算植入物对植入物周围皮质骨辐射剂量的影响。在距离≥100微米处，由于钛植入物，辐射剂量没有增加。然而，与植入物接触时（即细胞的第一层），辐射剂量急剧增加，高达无植入物时辐射剂量的3.5倍。此外，植入物小孔内新形成的骨由于植入物本身的高吸收而接收到的辐射剂量接近无植入物时辐射剂量的50%。
假设患者在6个月内接受了5次X射线图像检查，皮质骨-钛界面处的最大辐射剂量估计小于20 mGy（0.02 Gy）。
