Radiation-induced pulmonary injury: symptomatic versus subclinical endpoints

Abstract

Purpose : To assess the relationship between radiation (RT)induced pulmonary symptoms and subclinical changes in pulmonary functions tests (PFT) and radiographs. Materials and methods : A total of 184 patients irradiated between 1992 and 1998 were prospectively evaluated for RT-induced pulmonary symptoms, changes in computed tomography (CT) density, reductions in single photon emission CT (SPECT) perfusion, and changes in pulmonary functions tests (forced expiratory volume in 1s [FEV 1 ] and diffusion capacity to carbon monoxide [DLCO]). Comparisons between the evaluable patients with (N = 34) and without (N = 106) RT-induced pulmonary symptoms were made. Results : Within 6 months of RT, 80% of the RT-induced symptoms were noted. There was no association between the presence or absence of RT-induced pulmonary symptoms and the frequency of RT-induced radiographic changes (p = 0.53), or in the dose–response curve for RT-induced reductions in regional perfusion. Overall, RT-induced changes in SPECT images were more commonly seen than increased density changes on CT (p < 0.001). Most patients with pulmonary symptoms had relatively low pre-RT PFTs and experienced further declines following RT. Conclusions : Regional radiographic changes in CT-defined tissue density or SPECT-defined tissue perfusion are similar in patients with and without RT-induced pulmonary symptoms because these endpoints do not consider the volume of lung affected. RT-induced pulmonary symptoms are better related to post-RT PFT because they are an assessment of whole lung function. Additional studies are necessary to better define models that can predict the degree of radiation-induced changes in whole lung function.