Figure 6: Scores of relative Masson’s Trichrome staining intensity (Mean ± standard deviation) for upper and lower lung lobes in each group, as an indication of collagen deposits and development of fibrosis. A significant difference was observed in the collagen relative intensity of the upper and lower lobes of the control samples and the 12 Gy irradiated rats (**p<0.001); the lower lobe showed more collagen deposition. The differences in collagen deposition in the lower lobes of control and 12 Gy irradiated rats were significant (p<0.01) when compared to the lower lobes of 20 Gy irradiated rats. The differences in collagen relative intensities in the upperlobes of control rats were significant (p<0.001) when compared to the upper lobes of 16 Gy and 20 Gy irradiated rats. Control group, 12 Gy, 16 Gy were analysed at 24 weeks of age (16 weeks post irradiation) and 20 Gy at 12 weeks of age (4 weeks post irradiation).