The lungs are radiation-sensitive organs, and radiation pneumonitis (RP) is a condition in which patients whose lungs have received radiotherapy within a year develop pulmonary symptoms such as cough and dyspnea that persist for more than 2 weeks, along with lung imaging showing lamellar or streak-like shadows consistent with the irradiated field.
RP is an acute spontaneous immune-like response mediated by inflammatory factors and is a form of lymphocytic alveolitis. It often occurs after radiation therapy in patients with lung cancer, breast cancer, esophageal cancer, and malignant pleural mesothelioma. Acute RP usually occurs 1 to 3 months after radiotherapy, and can occur during or near the end of radiotherapy in patients treated with post-chemotherapy radiotherapy. Late radiation damage to the lungs is mainly manifested as fibrosis of the lung tissue and most often occurs about 6 months after irradiation.
Preferred glucocorticoid therapy
For suspected RP, inhaled hormones can be nebulized. For symptomatic patients, prednisone 1 mg/(kg・d) is recommended. Hormone therapy is ineffective in radiographic pulmonary fibrosis because the mechanism of hormone therapy is anti-inflammatory and immunosuppressive, which reduces exudation and production of pro-fibrotic factors, but does not improve fibrotic lesions that have already formed.
Classification of glucocorticoids
Short-acting (8-12 hours): hydrocortisone (cortisol, secreted by the body at 15-25 mg daily), cortisone
Medium-acting (12-36 hours): prednisone (prednisone), prednisolone (prednisone), methylprednisolone (methylprednisolone)
Long-acting (36 to 54 hours): dexamethasone, betamethasone
How to use the medication
Treatment principle: immediate, adequate amount and sufficient time of hormone use.
Low dose treatment is not effective and may lead to prolonged disease duration. After radiation therapy, glucocorticoid receptor expression in splenocytes is down-regulated, so adequate doses of hormones are needed.
In general, 2 weeks of symptoms of cough and shortness of breath, combined with a history of chest radiotherapy and imaging changes, is the best time to give hormone therapy.
Acute phase RP: Prednisone 30-60 mg/d or dexamethasone 16-20 mg/d can rapidly relieve the signs and symptoms within 24-48 hours, and gradually reduce the dose by 10-15 mg/d after improvement for a total course of about 3-8 weeks. For patients sensitive to hormone therapy, a short course (2 weeks) of methylprednisolone 20-40 mg shock therapy can be used to improve pulmonary exudation in a timely and effective manner. In addition, some studies have shown that the use of nebulized inhalation is less invasive and has a lower rate of secondary lung infections and sleep disturbances.
When to withdraw the drug
Some physicians withdraw medication too slowly for fear of rebound, which in turn prolongs the course of the patient’s illness and increases the risk of infection. The initial dose of prednisone is 20-66.7 mg/d, which is maintained (about 2 weeks) until remission and then reduced and stopped.
Hormone tapering may follow the principle of “first fast, then slow”.
For example, prednisone shock therapy can be reduced directly to 1 mg/(kg/d); the initial dose of 60 mg/d can be reduced directly to 40 mg/d, and then reduced by 10% or 5 mg of the original dose for 1 to 2 weeks, and the dose can be stopped only when it is less than 7.5 mg/d. Other researchers have recommended a “slow and easy” withdrawal method: withdraw 1/3 of the methylprednisolone first, then withdraw the remaining 1/2 after 2 days, and then withdraw the whole dose after 3-5 days, which was effective in a limited sample size (6 cases) without rebound and can be tried clinically.
Prevention is more important than treatment
The etiology of RP is unknown, treatment is limited, prevention is the main focus, and clinically relevant high-risk factors such as
Large irradiated lung volume, high dose, female, low KPS score, poor lung function before treatment, non-smoker, chemotherapy (application of bleomycin, gemcitabine, etc.) before radiotherapy, elderly and children. Preferred hormonal therapy is supplemented by symptomatic treatment including oxygen, expectoration and bronchodilators to keep the airway open and to protect the lungs during radiotherapy with amphotericin. Although RP is non-infectious, it is often associated with lung infection, so antibiotics are also necessary to prevent and treat infection. In the absence of infection, antibiotics should be used only as prophylaxis, and in case of co-infection, antibiotics should be selected according to the drug sensitivity results.