Radiation-induced pulmonary injury: symptomatic versus subclinical endpoints

Purpose: To assess the relationship between radiation (RT)-induced pulmonar y symptoms and subclinical changes in pulmonary functions tests (PFT) and r adiographs. Materials and methods: A total of 184 patients irradiated between 1992 and 1998 were prospectively evaluated for RT-induced pulmonary symptoms, change s in computed tomography (CT) density, reductions in single photon emission CT (SPECT) perfusion, and changes in pulmonary functions tests (forced exp iratory volume in 1 s [FEV1] and diffusion capacity to carbon monoxide [DLC O]). 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 pulm onary symptoms and the frequency of RT-induced radiographic changes (p = 0. 53), or in the dose-response curve for RT-induced reductions in regional pe rfusion. Overall, RT-induced changes in SPECT images were more commonly see n than increased density changes on CT (p < 0.001). Most patients with pulm onary symptoms had relatively low pre-RT PFI's and experienced further decl ines 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 volu me of lung affected. RT-induced pulmonary symptoms are better related to po st-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.