Pathogenesis of Radiation-Induced Pneumonitis In Patients with Chronic Obstructive Pulmonary Disease

Background: Chest radiation is a common therapeutic approach in the management of lung cancer, as well as in other malignancies, rendering radiation-induced pneumonitis a rather commonly reported adverse event. A large proportion of patients undergoing radiation have underlying chronic obstructive pulmonary disease (COPD). We aim to elucidate the pathogenetic pathways implicated in radiation-induced pneumonitis particularly in this subgroup of patients.

Methods: A literature search was performed in Pubmed to identify relative studies published until June 2011.

Results: The incidence of radiation-induced pneumonitis after conventional irradiation in COPD is about 7 to 10% in the moderate although symptomatic forms and about 1 to 3% in the severe forms. Radiation-induced pneumonitis seems to be an acute-phase reaction, taking primarily place in the most radiosensitive subunit of the lung, the alveolar/capillary complex. Reactive oxygen species, generated by radiation, initiate a cascade of molecular events that alter the cytokine milieu of the microenvironment, creating inflammation and chronic oxidative stress. COPD is characterized by a chronic inflammatory state in the lung, also generating reactive oxidant species. Biological markers intrinsic to the patient, such as early variations of certain cytokines (IL-6, IL-10, TGF-β) seem to be implicated and studies are under way to determine their role. The standard dose-volume metrics, such as V20, V13 and mean lung dose, are major factors influencing the clinical course of radiation-induced pneumonitis.

Conclusions: Understanding the underlying pathogenesis of radiation-induced pneumonitis may help improve optimal delivery of treatment plans, minimize the risks and increasing the therapeutic ratio in patients with COPD.