McChesney S L, Gillette E L, Powers B E
Department of Radiology and Radiation Biology, Colorado State University, Fort Collins 80523.
Int J Radiat Oncol Biol Phys. 1989 Jan;16(1):125-32. doi: 10.1016/0360-3016(89)90019-9.
Canine lungs were irradiated with a range of total doses given in 2, 3, or 4 Gy per fraction. Sequential histopathologic evaluations were done at 1, 3, 6, and 12 months. Pathologic changes in canine lungs were found to be similar to those found in other species demonstrating a clinically latent period, a pneumonitis phase, and late fibrosis and vascular damage. The relative impact of endothelial cell and pneumocyte injury on either early or late radiation injury of the lung is difficult to resolve. Therefore, it is not possible to define a target cell for lung injury at this time. The alpha/beta ratios determined in this study indicate that the target cell or cells associated with lung consolidation are slowly proliferating and represent late responding tissues. Lungs were evaluated histomorphometrically for alveolar air space and radiographically for alveolar consolidation at 6 months after irradiation. Alpha/beta ratios of 3 Gy and 4 Gy were calculated respectively. Both assays demonstrated an increasing effect on lung damage with increasing fraction size from 2 to 4 Gy. Application of the LQ model and use of alpha/beta ratios for calculation of dose adjustments remains theoretical. Clinical data are insufficient to define specific alpha/beta ratios for the various normal tissues at risk in radiation therapy. The data are sufficient to demonstrate the sparing effects of decreasing size of dose per fraction for late responding tissue. Results of this study suggest caution against the use of large doses per fraction for radiation therapy fields which include large lung volumes.
用每次分割剂量为2、3或4 Gy的一系列总剂量对犬肺进行照射。在1、3、6和12个月时进行连续的组织病理学评估。发现犬肺的病理变化与其他物种相似，表现出临床潜伏期、肺炎期以及晚期纤维化和血管损伤。内皮细胞和肺上皮细胞损伤对肺早期或晚期放射性损伤的相对影响难以确定。因此，目前无法确定肺损伤的靶细胞。本研究中确定的α/β比值表明，与肺实变相关的一个或多个靶细胞增殖缓慢，代表晚期反应组织。在照射后6个月时，对肺进行组织形态计量学评估以观察肺泡气腔，并进行影像学评估以观察肺泡实变。分别计算3 Gy和4 Gy的α/β比值。两种检测方法均显示，随着分割剂量从2 Gy增加到4 Gy，对肺损伤的影响增大。应用线性二次模型和使用α/β比值来计算剂量调整仍停留在理论层面。临床数据不足以确定放射治疗中各种正常危险组织的特定α/β比值。这些数据足以证明减少每次分割剂量对晚期反应组织的保护作用。本研究结果提示，对于包括大肺体积的放射治疗野，应谨慎使用大分割剂量。
