Chapter 57: Radiation Pneumonitis

INTRODUCTION

The discovery of x-rays by Roentgen in 1895 and of radium by the Curies in 1898 revolutionized medicine at the turn of the 20th century.^1–3 Roentgen’s first paper on x-rays illustrated the power of diagnostic imaging with a remarkably detailed radiographic image of Frau Roentgen’s hand. As researchers around the world built vacuum tubes and acquired radioactive sources for their studies, it rapidly became apparent that these invisible radiations could produce dangerous, and even lethal, injuries.^1–3 Erythema, chronic dermatitis, ulceration, loss of hair, and eye injuries were soon reported in patients who received large doses of radiation during prolonged fluoroscopy procedures, and further toxicities were observed in physicians, technicians, and scientists exposed to unshielded radiation sources. The development of these radiation injuries suggested that radiation might be useful in the treatment of cancer; indeed, patients with cancer were treated with radiation therapy as early as 1896.^1–3 Radiation was found to inhibit the growth of tumors, but this benefit came with the cost of injury to normal tissues within the irradiated areas. The relative sensitivity of the lung to injury from radiation became apparent early in the development of radiation oncology. The clinical syndromes of dyspnea, cough, fever, and radiographic infiltrates occurring weeks to months after irradiation of the thorax were dramatic enough to be described as early as 1922.⁴

For clinicians interested in pulmonary medicine, understanding radiation pneumonitis is important. Because the chemical mediators of radiation effects, both beneficial and harmful, are free radicals, understanding the pathway leading to radiation injury in the lung can be useful in elucidating mechanisms of other lung injuries.^5,6 In addition, understanding radiation pneumonitis has practical value to physicians in many areas of medicine. Nearly 40% of men and women in the United States will be diagnosed with cancer at some point in their lifetimes, and the majority of these patients will be permanently cured of their malignancies.⁷ Approximately 60% of all patients with cancer receive radiotherapy at some point in the treatment of their malignancies, and radiotherapy will remain an important component of cancer treatment for the foreseeable future. Because of this, every physician can expect to care for many patients who are receiving radiotherapy or have received radiotherapy at some point in the past.

In addition to an association with acute or subacute pulmonary disease, radiation can lead to chronic toxicities. For instance, respiratory diseases are known to be a cause of increased late morbidity and mortality in the survivors of the atomic bombs in Hiroshima and Nagasaki.⁸ Additionally, studies of plutonium workers have shown an excess incidence of pulmonary fibrosis, demonstrating lung injury may be produced by inhalation of insoluble particulate radionuclides that are deposited in lung tissue and produce long-term irradiation of the tissue.⁹ Radiation injury to lung can occur not only through radiotherapy but also through exposure from occupations, accidents, or acts of war or ...