Lung toxicity following radiation therapy (RT) for thoracic neoplasms shows a wide range of severity, with different temporal occurrence and evolution on computed tomography (CT) according to the fractionation scheme. Radiation-induced lung injury (RILI) may appear early or later after treatment completion and may increase over time or tend to resolve or stabilize. RILI in lung neoplasms is often indistinguishable from the treated lesion, thus preventing the application of size-based criteria to assess treatment response and local recurrence. In this chapter, we will focus on RT techniques and applications in lung neoplasms and lung toxicity, described in terms of risk factors, CT characteristics, and clinical-radiological grading scales. Differential diagnoses and issues related to the prompt recognition of local recurrence will be discussed. Finally, the applications of RT in other thoracic neoplasms and radiation-induced toxicities in thoracic structures other than the lungs will be briefly outlined.