Allal A S, Richter M, Russo M, Rouzaud M, Dulguerov P, Kurtz J M
Division of Radiation Oncology, University Hospital, Geneva, Switzerland.
Int J Radiat Oncol Biol Phys. 1998 Jan 1;40(1):215-9. doi: 10.1016/s0360-3016(97)00587-7.
To evaluate dose variations at bone/titanium interfaces in an experimental model designed to simulate postoperative radiotherapy in patients with mandibular reconstructions using a titanium hollow-screw osseointegrating reconstruction plate (THORP) system.
The model consisted of a 25 x 25 x 10 mm3 block of fresh bovine femoral diaphysis, to the surface of which a segment of THORP system reconstruction plate was fixed by means of a solid titanium screw 4 mm in diameter and 10 mm in length. Using specially designed thermoluminescent dosimeters (TLD) 2 mm in diameter and 0.13 mm in thickness, dose measurements were carried out at four distances from the screw axis (0.1, 0.3, 0.6, and 1 mm). 60Co and 6-MV photon beams were used at incidences both perpendicular and parallel ("axial") to the screw axis.
For 6-MV X-ray beams incident perpendicular to the screw axis, the maximum dose enhancement (due to backscatter) and the maximum dose reduction (due to attenuation) at the bone/titanium interface were 5% (+/- 2%) and 6% (+/- 2%), respectively. The corresponding values for 60Co beams were 6% (+/- 5%) and 10% (+/- 5%). For the axial incidences, a maximum dose enhancement of 5-7% was noted for both 6-MV X-rays and 60Co for beams incident on the surface containing the THORP plate segment, whereas beams incident on the opposite surface induced only a very small dose enhancement (2-3%).
Using a new experimental model, TLD measurements showed only marginally significant dose variations at bone/titanium interfaces around THORP screws, all measured values being very close to the uncertainty limits (+/- 5%) associated with the method. For both 60Co and 6-MV beams, dose variations appeared smaller for axial than for perpendicular incidences. Because photon beams used in head and neck cancer treatment are most often directed parallel to the screw axes, these results suggest that failures of prosthetic osseointegration are unlikely to be explained by an overdosage at the bone/titanium interface.
在一个实验模型中评估骨/钛界面处的剂量变化，该模型旨在模拟使用钛空心螺钉骨整合重建板（THORP）系统进行下颌骨重建的患者术后放疗情况。
模型由一块25×25×10立方毫米的新鲜牛股骨干组成，在其表面通过一根直径4毫米、长度10毫米的实心钛螺钉固定一段THORP系统重建板。使用专门设计的直径2毫米、厚度0.13毫米的热释光剂量计（TLD），在距螺钉轴线四个距离（0.1、0.3、0.6和1毫米）处进行剂量测量。60钴和6兆伏光子束分别以垂直和平行（“轴向”）于螺钉轴线的入射角使用。
对于垂直于螺钉轴线入射的6兆伏X射线束，骨/钛界面处的最大剂量增强（由于反向散射）和最大剂量降低（由于衰减）分别为5%（±2%）和6%（±2%）。60钴束的相应值为6%（±5%）和10%（±5%）。对于轴向入射角，入射到包含THORP板段表面的6兆伏X射线和60钴束的最大剂量增强为5 - 7%，而入射到相对表面的束仅引起非常小的剂量增强（2 - 3%）。
使用新的实验模型，TLD测量显示THORP螺钉周围骨/钛界面处的剂量变化仅略有显著意义，所有测量值都非常接近该方法相关的不确定限度（±5%）。对于60钴和6兆伏束，轴向入射角的剂量变化似乎比垂直入射角的小。由于头颈癌治疗中使用的光子束最常平行于螺钉轴线，这些结果表明假体骨整合失败不太可能由骨/钛界面处的过量照射来解释。
