[Repair mechanisms of the lung--experimental and clinical results]

The effect of dose and time and of the RBE on the pulmonary reaction to radiation has been studied by means of trials with young pigs. 70 animals received a fractionated (five and 15 fractions) telecobalt irradiation of the right lung over total treatment periods T of five, 23, and 35 days. The influence of dose and time on the pulmonary reaction to radiation is defined at the ED50 level (effective dose, after which 50% of animals will suffer from radiopathy) by a proportionality of D approximately N0.32 X T0.05. An alpha/beta value of 3.7 Gy is calculated according to the LQ model. An RBE value of 4.0 to 4.1 was determined in 38 animals treated over five and 35 days with the 6.2 MeV neutrons of the cyclotron Rossendorf. The experimentations on animals allow to classify the lung reaction as late effect. The clinical results found in literature show that this classification is also valid for human lung reaction to fractionated radiotherapy. So it is not possible to achieve a considerable increase of the pulmonary tolerance dose by increasing the total treatment period. The best sparing of the respiratory organ is obtained by an application of small single doses which allows to profit from the large repair capacity of pulmonary tissue. These results, as well as our considerations regarding the latent time between therapy and lung reaction, and some trials on laboratory rodents allow to speak of a radiogenic pneumopathy with the proprieties of a late reaction characterized by a pneumonitis appearing previously and changing into pulmonary fibrosis.