An Overview of Radiation Pneumonitis

A woman uncomfortably holding her chest

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Radiation pneumonitis is an inflammation of the lungs due to radiation therapy or stereotactic body radiotherapy (SBRT) for cancer. This side effect of radiation therapy occurs in roughly 15-40% of people who go through radiation therapy for lung cancer but can also result from radiation to the chest for breast cancer, lymphomas, thymic tumors, or esophageal cancer. Symptoms most commonly occur 2 months to 3 months after completing radiation therapy, and can include shortness of breath, chest pain (often sharp), a cough, and fever. The condition can often be diagnosed with a chest X-ray, but a high index of suspicion is important to not miss the diagnosis. With treatment including steroids, most people recover without any lasting effects. That said, without treatment, the condition may result in pulmonary fibrosis (scarring) of the lungs. Fortunately, recent research has found that the antibiotic Biaxin (clarithromycin) can mitigate radiation pneumonitis, at least for people with lung cancer who are undergo the specialized type of radiation therapy known as SBRT.


It is important to be aware of radiation pneumonitis, because symptoms can be very similar to those caused by lung cancer alone, or can be mistaken for an infection such as pneumonia. Many people simply tolerate these symptoms as expected, yet radiation pneumonitis is a good reminder that you should talk to your oncologist about any symptoms you note. As noted, symptoms are most likely to occur 2 months to 3 months after radiation, but may occur in as little as a month, or not until 12 months after completion. Common symptoms include:

  • Shortness of breath that is usually more notable with exercise
  • A Cough which can be dry or produce mucus (since many people with lung cancer have a cough at times, it's important to note any change in your cough, whether it is more frequent, harsher, or more uncomfortable)
  • Low-grade fever

In some cases, no symptoms are present, and the diagnosis is made by the appearance of inflammation on a chest x-ray alone. In other cases, symptoms can be severe, with severe respiratory distress that can resemble adult respiratory distress syndrome.

Causes and Risk Factors

Radiation causes the lungs to produce less of the substance surfactant. Surfactant works to keep the lungs expanded when we exhale and increases the surface area of the lungs available for the exchange of oxygen and carbon dioxide. It is the lack of surfactant in premature babies which often results in respiratory distress.

Some people are more at risk than others of developing radiation pneumonitis. Conditions which increase the risk include:

  • Concurrent (meaning at the same time) radiation therapy and chemotherapy. Radiation pneumonitis (RP) is more common in people receiving concurrent radiation and chemotherapy than those receiving sequential (at different times) radiation and chemotherapy. If this is alarming it's important to look at factors other than this complication. In a 2009 study, researchers found that people with stage 3 lung cancer who received concurrent radiation and chemotherapy had double the survival after 5 years. Other studies have also suggested improved survival when the treatments are used together.
  • People who have other lung diseases, such as COPD, are at an increased risk.
  • Older people are more likely to develop radiation pneumonitis than younger people.
  • The amount of tissue treated. The risk of radiation pneumonitis increases with the area of the chest that is treated. It is also more common when the middle and lower lobes of the lungs are treated than with treatment of upper lobe lung cancers.
  • People who receive the chemotherapy drugs Paraplatin (carboplatin) and Taxol (paclitaxel) are more likely to develop radiation pneumonitis.


Lab tests may show signs of inflammation, such as an increased white blood cell count. Results of a test that looks for inflammation, called a sed-rate, may also show non-specific elevations above normal. A chest x-ray can show the characteristic appearance of radiation pneumonitis and may suggest that you need to be treated, even if you are not having any symptoms. Chest X-rays findings, however, do not always correlate with the degree of symptoms a person is experiencing.

Oximetry may show low blood oxygenation, and pulmonary function tests may show reduced lung volumes and stiffness of the lungs.

Differential Diagnosis

Other conditions may have symptoms very similar to radiation pneumonitis, including pneumonia, pulmonary emboli (blood clots in the legs that break off and travel to the lungs), or the growth or spread of cancer in the lungs.


Treatment is aimed at decreasing the inflammation. Corticosteroids, such as prednisone, are given until the inflammation subsides and then slowly decreased over time. According to a 2018 study, the use of the antibiotic Biaxin (clarithromycin) not only reduced the number of people with lung cancer who developed radiation pneumonitis who underwent stereotactic body radiotherapy (SBRT), a type of radiation therapy in which a high dose of radiation is delivered to a small amount of tissue, but appeared to prevent the development in many people. Other treatments may be used depending upon the location. For example, with radiation esophagitis, medications such as proton pump inhibitors, changes in diet, and local anesthetics to help with pain may be used.


Radiation pneumonitis usually resolves with treatment and is only rarely fatal. If it goes untreated or persists, it can lead to pulmonary fibrosis (scarring of the lungs), one of the possible long-term side effects of radiation therapy.


Research is ongoing looking for ways to reduce the risk of radiation pneumonitis among people going through radiation for lung cancer. Thus far it appears that the intake of soy isoflavone (eating soy-based foods such as tofu) may decrease the risk of radiation pneumonitis. The way this occurs is through decreasing inflammation, so it's unlikely that the intake of soy-based foods would interfere with the purpose of radiation therapy—eliminating cancer cells—but it's important to talk to your radiation oncologist about this, and any other suggestions she may have about lowering your risk.

For those who will be having stereotactic body radiotherapy (SBRT), a 2018 study found that the use of the antibiotic Biaxin (clarithromycin) significantly reduced the severity and may actually prevent the development of radiation pneumonitis.

Bottom Line

Radiation pneumonitis is very common in people who are treated for cancers such as lung cancer and breast cancer. Thankfully, with treatment, the condition often resolves without going on to cause radiation fibrosis. The most important thing you can do is be aware of the possible symptoms, and talk to your doctor if you experience any of these. As a final note, many of the symptoms may overlap with symptoms of your cancer or side effects of other treatments. Always talk to your doctor about any symptoms and be your own advocate for your cancer care. You are not being a whiner or a problem patient to bring up these concerns, and your doctor will recognize, instead, that you are being an active and involved participant in your care.

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