Morphometric study on late effect of 131I, 132I on rat thyroid gland (study on gland level)

Changes are reported in three dimensional stereo logic parameters of rat thyroid glands at 20 months after injury induced by 131I, 132I with image analysis and morphometric methods. The results showed that colloid and follicular volume density and surface area density of various dosage groups were all significantly smaller than those of the control (0 dose) group, and were dose-dependent (P<0.01). However the volume density of interstitial tissue was negatively dose-dependent (P<0.01). The colloid and follicular specific surface area of various dosage groups were all significantly larger than those of the control group (P<0.01), indicating colloid and follicular volumes were decreased. It is confirmed that by the semi-increase or semi-reduction dose D50 calculated from the regression equation of volume density, surface area density, and absorbed dose that the relative biological effectiveness (RBE) of 132I was 10∼25-fold of 131I, i.e., with same irradiation dose, the extent of injury induced by 132I would be 10∼25 times larger than that by 131I