Lung cancer has a known relationship with smoking and is one of the leading causes of cancer-related death worldwide. Although the number of studies discussing lung cancer is vast, treatment efficacy is still suboptimal due to the wide range of factors that affect patient outcome. This review aims to collect information on lung cancer treatment, specially focused on radiation therapy. It also compiles information regarding the influence of radiotherapy on the immune system and its response to tumour cells. It evaluates how immune cells react after radiation exposure and the influence of their cytokines in the tumour microenvironment. The literature analysis points out that the immune system is a very promising field of investigation regarding prognosis, mostly because the stromal microenvironment in the tumour can provide some information about what can succeed in the future concerning treatment choices and perspectives. T cells (CD4+ and CD8+), interleukin-8, vascular endothelial growth factor and transforming growth factor-β seem to have a key role in the immune response after radiation exposure. The lack of large scale studies means there is no common consensus in the scientific community about the role of the immune system in lung cancer patients treated with radiotherapy. Clarification of the mechanism behind the immune response after radiation can lead to better treatments and better quality life for patients.