高剂量格栅状放疗技术及应用

The application of high-dose grid radiotherapy technique

高剂量格栅状（Grid）放疗技术是通过格栅准直器或者MLC将照射野均匀分割成等间隔的小射线束,实施单次大剂量照射（10～25 Gy）,在靶区内形成非均匀的高低剂量区,剂量学上表现为峰谷效应（peak-to-valley effect）。随着3DRT技术的出现,二维格栅状治疗技术演变为三维的点阵式（Lattice）治疗技术。它通过不同形式的三维聚焦,在肿瘤内部形成多个空间上呈点阵式分布的球状高剂量区,球状高剂量区之间的区域剂量迅速跌落,形成三维非均匀的适形剂量分布。和二维Grid技术相比较,三维Lattice技术可以产生更明显的峰谷效应,更大程度地降低了肿瘤周围正常组织的剂量。实验数据表明,该照射技术可以刺激旁观者效应,增加内皮细胞死亡和免疫原性远隔效应,从而增强对肿瘤细胞的杀灭,进一步提高对局部和远处肿瘤的控制。Lattice技术在中晚期大肿瘤的姑息治疗上有明显的潜力,但是仍需要更多放射生物学机制和临床数据的支持。

High dose grid radiotherapy （GRID） refers to a single fraction of high-dose radiation （10-25 Gy） in which, beams are divided into multiple small beam lets through a grid collimator or MLC, resulting in non-uniform dose distribution of high and low dose area （“peak-to-valley” effect） in the target volume. Recently, as 3D radiotherapy （3DRT） technology emerged, the 2D GRID has been reconfigured into 3D dose LATTICE whereby high doses are concentrated at each lattice vertex within the radiation target volume with drastically lower dose between vertices through multiple focused non-coplanar beams with different radiation techniques. Compared with 2D GRID therapy, 3D LATTICE shows significant effect on “peak-to-valley” and minimizes radiation to surrounding tissues.Experimental and clinical data have shown that LATTICE therapies can reduce toxicity to normal tissue while stimulating bystander effects, endothelial cell death and immunogenic abscopal effects leading to enhanced killing of tumor cells and further improve the control of the local and distant disease. The clinic experience with LATTICE, although limited, has demonstrated favorable outcomes, especially for treating bulky tumors and palliative intend. The exact mechanism of the clinical advantages by LATTICE is not explicitly known and a more comprehensive biological study and clinical trials are called should be carried out.