QUANTIFICATION OF RADIATION-INDUCED REGIONAL LUNG INJURY WITH PERFUSION IMAGING

Purpose: To better understand the dose and time dependence of radiatio n therapy (RT)-induced regional lung dysfunction as assessed by change s in regional lung perfusion, Methods and Materials: Patients who were to receive RT for tumors in and around the thorax, wherein portions o f healthy lung would be incidentally irradiated, were prospectively st udied. Regional function was assessed pre- and post-RT with single pho ton emission computed tomography (SPECT) lung perfusion scans, obtaine d following the intravenous administration of similar to 4 mCi of tech netium-99m macroaggregated albumin, Pre-RT computed tomography (CT) sc ans were used to calculate the three-dimensional (3D) dose distributio n, reflecting tissue density inhomogeneity corrections. Each SPECT sca n was correlated with the pre-RT CT scan, and the 3D dose distribution , Changes in regional lung perfusion were correlated with regional RT dose, at various time intervals following radiation, Results: The data from 20 patients (7 breast cancer, 5 lymphoma, 1 esophagus, 1 sarcoma , and 6 lung cancer) have been analyzed. Patients with gross intrathor acic lung cancers causing obstruction of regional pulmonary arteries w ere not included, For most patients, there is a statistically signific ant dose-dependent reduction in regional blood flow at all time points following radiation, While a time dependence is suggested in the high dose range, the limited amount of data prevents meaningful statistica l evaluation, Conclusions: Radiation therapy-induced regional lung dys function occurs in a dose-dependent manner and develops within 3-6 mon ths following radiation, In contrast to classical ''sigmoid'' dose-res ponse curves, described mainly for changes following whole lung irradi ation, these data suggest a more gradual relationship between regional dysfunction and RT dose. Retraction of irradiated lung with secondary movement of unirradiated lung into the ''3D-defined irradiated volume '' may have introduced inaccuracies into this analysis. Additional stu dies are currently underway to assess this possibility and better refi ne this dose-response curve. Studies are underway to determine if chan ges in assessments of whole lung function, such as pulmonary function tests, can be predicted by summing the regional changes observed. (C) 1997 Elsevier Science Inc.