The lungs are a common site of many different problems, including complications from cancer itself or secondary problems related to cancer treatment. To complicate this situation further, respiratory symptoms are vague and can be difficult to differentiate. In addition, monitoring systems are limited. As a result, in terms of treatment-induced pneumonitis, it is difficult to come up with a final decision. Furthermore, basically, diagnosis of treatment-related toxicity is a “process of elimination” achieved by excluding other potential causes.