From the Guidelines
Radiation pneumonitis typically occurs during or 2-6 months after radiotherapy, with symptoms such as cough and dyspnea, and can progress to pulmonary fibrosis 6-12 months after completion of radiotherapy. The condition follows a predictable time course, beginning with an acute phase characterized by nonproductive cough, exercise-induced dyspnea, low-grade fever, and chest pain, as described in the study by 1. This acute phase usually lasts 2-3 weeks and may resolve spontaneously or progress to a more severe presentation. If untreated or severe, radiation pneumonitis can evolve into chronic radiation fibrosis, which represents permanent lung damage. The risk and severity depend on radiation dose, volume of lung irradiated, fractionation schedule, concurrent chemotherapy, and patient factors such as pre-existing lung disease. Patients receiving thoracic radiation should be monitored closely during this time window, particularly those with risk factors, as suggested by 1. The pathophysiology involves radiation-induced damage to pneumocytes and vascular endothelium, triggering an inflammatory cascade that can lead to fibrotic changes if the inflammatory process is not controlled.
Some key factors that influence the development of radiation pneumonitis include:
- Radiation dose and volume of lung irradiated
- Fractionation schedule
- Concurrent chemotherapy
- Patient factors such as pre-existing lung disease
- The use of immunotherapy, which has been associated with an increase in pulmonary toxicities, as noted in 1
It is essential to note that the symptoms of radiation pneumonitis can be similar to those of other conditions, such as pulmonary infections, COPD exacerbations, heart failure, and cardiac arrhythmias, making accurate diagnosis and monitoring crucial, as highlighted in 1. The treatment of radiation pneumonitis typically consists of symptomatic treatment, anti-inflammatory drugs, and treatment of comorbid diseases, as recommended in 1.
From the Research
Time Course of Radiation Pneumonitis
- Radiation pneumonitis usually becomes clinically apparent from 2 to 6 months after completion of radiation therapy 2
- The syndrome may resolve spontaneously or may progress to respiratory failure 2
- The time course for the development of radiation fibrosis is later than that for radiation pneumonitis, usually present by 1 year following irradiation, but may not become clinically apparent until 2 years after radiation therapy 2
Factors Influencing the Time Course
- The use of systemic corticosteroids may be effective therapy if started early in the course of the disease 2, 3
- Concurrent use of moderate dose prednisone and azathioprine during the periradiotherapy period does not prevent the development of either radiation pneumonitis or classic radiation pneumonitis 3
- Factors such as Eastern Cooperative Oncology Group performance status, forced expiratory volume in 1 second, and previous planning target volume location may be associated with the incidence of severe radiation pneumonitis 4
- Dosimetric factors, such as lung volume receiving ≥20 Gy (V20), and tumor location may predict the development of symptomatic pneumonitis 5