[Late radiation fibrosis in rat lung following protons and 250 kV X-rays irradiation].

To investigate the biological effectiveness of proton beams in the development of pulmonary fibrosis the lungs of male 7-week-old Wistar rats were locally irradiated with a single dose of 10-50 Gy of 250 kV X-rays and modulated, 250 MeV protons at Particle Radiation Medical Science Center (PARMS). Animals were sacrificed serially after 3, 6, 9 and 12 months at which times the development of the fibrotic lesion in alveolar walls and peribronchial connective tissues was assessed quantitatively by analysis of microscopic images of Azan-Mallory stained sections. Fibrosis index (FI) values in alveolar walls and peribronchial tissues were defined as the fraction (in percent) of a specific image area, the gray level of which represents collagen deposits. Using this FI values, the increase of fibrotic lesion following 0-40 Gy of X-rays irradiation as a function of time were observed better in alveolar walls than in peribronchial tissues. Compared with 250 kV X-rays, 30 Gy of proton beams irradiation produced less increase in the time course of FI values of alveolar walls and dose-response curve at 12 months later suggested that the fibrotic lesion in alveolar walls after protons exposure of the doses above 30 Gy might develop more slowly.