The hydroxyproline content in the lung tissue of young pigs after fractionated irradiation with photons or neutrons.

The radiation response of normal lung tissue was studied in 99 young pigs. Five fractions of Co-60-photons and of neutrons with an average energy of 6.2 MeV were applied during overall treatment times of five and 35 days respectively. The irradiation field comprised the whole of the right lung. At eight to ten weeks and at eight to 13 months animals were sacrificed and the removed lungs were investigated histopathologically and biochemically. Radiation induced fibrosis was evaluated by determining the ratio of hydroxyproline concentration of irradiated and non-irradiated lung in the same animal. Above a threshold there was a significant increase of the hydroxyproline ratio with increasing doses. Histopathological findings and hydroxyproline ratio were in close agreement. RBE values between 3.8 and 4.5 were calculated in accordance with the results using the other criteria of lung damage in our studies on pigs.