REGIONAL DOSE-RESPONSE TO PULMONARY IRRADIATION USING A MANUAL METHOD

Purpose: To better understand the dose dependence of radiation therapy (RT)-induced changes in regional lung perfusion and tissue density, u sing a manual method to reduce inaccuracies that might be present in p reviously described automated methods. Materials and methods: Patients who were to receive RT for tumors in and around the thorax, wherein p ortions of healthy lung would be incidentally irradiated, were prospec tively studied. Changes in regional perfusion and tissue density were assessed by comparison of pre- and post-RT single photon emission comp uted tomography (SPECT), lung perfusion scans and computed tomography (CT) scans, respectively. The three-dimensional dose distribution was calculated on the pre-RT CT scan and correlated to the other scans via image registration. Study volumes were defined by hand and individual ly visualized on pre- and post-RT scans. The manually generated dose r esponse data were compared to data generated using automated methods. The relationship between CT density and SPECT perfusion was also deter mined. Results: Thirteen patients with lung cancer were evaluated for changes in tissue density and 11 patients were evaluated for changes i n regional perfusion at 12 months post-RT. In general, density increas es with increasing regional dose, with marked changes at >60 Gy. Regio nal perfusion decreases with increasing regional dose. In the low dose regions, relative perfusion increases by 35% on average. Manually mea sured dose responses correlated well with those determined automatical ly. The relationship between regional perfusion and CT density indicat es a wide range of perfusion over a narrow range of CT density, with m arkedly reduced perfusion at CT densities of > - 600 and < - 900 H. Co nclusions: The manually generated CT density dose response data broadl y agree with data previously generated using automated methods. The ma nually generated perfusion dose response data are in fairly good agree ment with automated data, lending credibility to the accuracy of the a utomated methods. Regional perfusion is markedly diminished where CT d ensity is outside the range of normal lung tissue. (C) 1998 Elsevier S cience Ireland Ltd. All rights reserved.