Rosengren B, Wulff L, Carlsson E, Carlsson J, Montelius A, Russell K, Grusell E
Department of Radiation Sciences, Uppsala University, Sweden.
Acta Oncol. 1991;30(7):859-66. doi: 10.3109/02841869109091835.
It has been claimed that implanted metals can cause backscatter radiation in radiation therapy with a dose enhancement at the bone-metal and tissue-metal interfaces on the beam entrance side. Theoretical calculations and experimental measurements with ionization chambers have indicated that such effects might be significant. Titanium implants are increasingly used in oral and maxillo-facial surgery for reconstruction purposes. A more detailed knowledge of backscatter-induced effects is therefore desired when head and neck cancers in patients with implants are treated with radiotherapy. We have made comparisons of cell survival after irradiation of two types of cultured cells grown directly on titanium metal and on plastic control supports. The cell cultures were irradiated with either 60Co photons or range modulated protons. No significant differences in the colony-forming capacity were found between the irradiated cells grown on titanium and those grown on plastic control supports. This was the case for both radiation types and the results were also observed to be dose-independent. The only observed phenomena were that the two cell-lines differed in radiosensitivity and that protons gave higher biological effects than gamma radiation. The results show that there were no significant changes in cell survival at the interface between the tissue equivalent medium and titanium support indicating that a dose increase induced by backscatter radiation, which possibly could demolish the osseointegration or induce osteoradionecrosis, are minimal when high energy photons or range modulated protons are applied.
有人声称，植入金属在放射治疗中会导致反向散射辐射，在束流入射侧的骨 - 金属和组织 - 金属界面处剂量增强。理论计算和电离室实验测量表明，这种效应可能很显著。钛植入物越来越多地用于口腔颌面外科的重建目的。因此，当对植入物患者的头颈癌进行放射治疗时，需要更详细地了解反向散射引起的效应。我们比较了直接生长在钛金属和塑料对照支架上的两种培养细胞照射后的细胞存活率。细胞培养物用60Co光子或射程调制质子进行照射。在钛上生长的照射细胞与在塑料对照支架上生长的照射细胞之间，未发现集落形成能力有显著差异。两种辐射类型均是如此，且结果也与剂量无关。唯一观察到的现象是两种细胞系的放射敏感性不同，并且质子比γ辐射具有更高的生物学效应。结果表明，在组织等效介质与钛支架的界面处，细胞存活率没有显著变化，这表明当应用高能光子或射程调制质子时，由反向散射辐射引起的剂量增加（可能会破坏骨整合或诱发放射性骨坏死）极小。
