放疗诱导瘦体组织减少的机制及临床意义

The mechanism of radiation induced lean body mass loss and its clinical significance

放射治疗过程中常常伴随着营养不良的发生。营养不良的发生概率、发生时间、严重程度等随着肿瘤类型、疾病分期、治疗手段不同而有所差异。营养不良不仅表现在体重丢失,也表现为LBM减少。LBM又被称为去脂体重,即去除脂肪以外身体其他成分的重量,它由身体细胞重量、细胞外水分和去掉脂肪后的固体成分组成,其中肌肉和骨骼是主要的组成部分。许多动物学实验表明:在受到放射线照射后,肌肉也会出现急性萎缩反应,表现为肌球蛋白含量减少、肌球蛋白重链比例变化等,并且与放射线剂量有关。在临床研究中也观察到放疗后肌肉含量减少,并与预后显著相关。放射线所致的骨质流失也是导致LBM下降的重要因素之一。既往认为放射线所致骨质流失常表现为晚期不良反应,但实验室研究发现,在放射治疗的早期即可出现骨质流失,并与放射剂量显著相关。综上所述,放射线可导致肌肉萎缩,骨质流失,从而导致LBM减少,增加患者死亡风险,严重影响患者生活质量。由于放疗对肌肉、骨质的作用有部位及剂量特异性,在临床实践中对于长骨、重要肌肉等部位进行大剂量放射治疗时,应慎重考虑肌肉萎缩、骨质流失带来的相关不良后果,从而取得最佳的治疗获益比。

Radiotherapy often accompanies with malnutrition.The incidence,the time of occurrence,severity of malnutrition and so on were varied with different types of tumor,disease stages and treatment methods.Malnutrition is not only a decrease in body weight,but also a loss in lean body mass.Lean body mass is also called fat free weight,namely the mass of body after removal of fat,which is composed of cells,extracellular water and other solid components.Muscle and bones are main components of lean body mass.Many animal experiments showed that after irradiation,the muscles would appear acute atrophy,performed by decreasing of myosin and changes in proportions of myosin heavy chain,and this phenomenon was affected by radiation doses.In the clinical studies,the decrease of muscle content after radiotherapy was also observed,which was significantly related to prognosis.Bone loss caused by radiation is also one of the important factors that lead to loss of lean body mass.In the past,it was considered to be a late adverse reaction induced by radiation.However,it was found that bone loss occurred in the early stage of radiation therapy,and it was significantly affected by the radiation dose.In summary,radiation can lead to muscle atrophy,bone loss,resulting in loss of lean body mass,which increases the risk of death and affects the quality of life of patients.Because of the effects of radiotherapy variesin different muscles and bones,in clinical settings,radiotherapists should consider the adverse effects caused by muscle atrophy and bone loss when applying radiation to important bones and muscles,thus achieving optimistic treatment effect.