Quantification of radiation-induced regional lung injury with perfusion imaging

Abstract

Purpose : To better understanding the dose and time dependence of radiation therapy (RT)-induced regional lung dysfunction as assessed by changes in regional lung perfusion. Methods and Materials : Patients who were to receive RT for tumors in and around the thorax, wherein portions of healthy lung would be incidentally irradiated, were prospectively studied. Regional function was assessed pre- and post-RT with single photon emission computed tomography (SPECT) lung perfusion scans, obtained following the intravenous administration of ∼4 mCi of technetium-99m macroaggregated albumin. Pre-RT computed tomography (CT) scans were used to calculate the three-dimensional (3D) dose distribution, reflecting tissue density inhomogeneity corrections. Each SPECT scan 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 intrathoracic lung cancers causing obstruction of regional pulmonary arteries were not included. For most patients, there is a statistically significant 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 statistical evaluation. Conclusions: Radiation therapy-induced regional lung dysfunction occurs in a dose-dependent manner and develops within 3–6 months following radiation. In contrast to classical “sigmoid” dose-response curves, desribed mainly for changes following whole lung irradiation, these data suggest a more gradual relationship between regional dysfunction and RT dose. Retraction of irradiation lung with secondary movement of unirradiated lung into the “3D-defined irradiated volume” may have introduced inaccuracies into this analysis. Additional studies are currently underway to asses this possibility and better refine this dose-response curve. Studies are underway to determine if changes in assessment of whole lung function, such as pulmonary function tests, can be predicted by summing the regional changes observed.