There are various conditions which warrant the application of this test. If the cancer is invasive in nature and has infected the lungs, a chest x-ray will help determine in the course of the treatment the body’s response to the therapy. Chemotherapy is also given to the breast cancer patient, some patients develop fever during chemotherapy. An X-ray during/post chemotherapy helps in checking for pneumonia. Radiation therapy often leads to the inflammation of the patient’s lungs. The symptoms would include shortness of breath. An x-ray in such cases can help determine inflammation in the lungs.