Quantitative morphology of late renal radiation injury.
Late radiation injury manifests itself in all morphologic compartments of the kidney, but loss of cell mass is most significant in the proximal convoluted tubules. Development of an end stage or nonfunctional kidney requires 12 or more months after single fraction X ray exposures of about 12 Gy (2, 5, 13) and is associated with marked morphologic alterations of renal tubules. Radiation induced changes were studied at 6 months after irradiation, a time interval when histological alterations appear minor, but in previous studies were shown to correlate with the later end stage alterations (5, 8, 9). Renal alterations were graded objectively based on renal weight, variation in size of tubule cell nuclei, and glomerular nuclear volume fraction. Irradiation was associated with loss of renal weight, increased variability of tubule nuclear size, and previously unappreciated changes in glomerular nuclear volume fraction. A classification index derived from a weighted combination of renal weight ratio and tubule cell nuclear variability correlates with radiation dose and with previously established subjective histologic grading of renal damage, and allows objective comparisons of various fractionation schedules.