Objective: Evaluating micro CT as a method of measuring healing in irradiated rat calvaria defects (non-critical size defects). We examined the %bone healed of bony defects as opposed to evaluation with conventional radiographs. Methods: Animals were divided into groups based on radiation dose and interval between radiation and surgery. Radiation doses used were 0Gy, 12Gy, and 18Gy. Time interval between radiation and surgery was 4hr or 10 days. 3mm bony defects were made in each parietal bone. Collagen sponge was used to fill right side defects. Wounds were closed with chromic gut sutures. Animals were sacrificed at 3, 7, 14, and 21 days post surgery. Following sacrifice, calvaria were stored in formalin. All 28 day calvarial specimens were scanned using high-resolution desktop microtomographic imaging system (µCT40, Scanco Medical AG, Basserdorf, Switzerland). Diameter and depth of initial defect were measured to calculate defect volume. Percentage of defect healed was given as the ratio of healed bone volume to defect volume. Radiographs of defects were examined using Image J™ analysis. Results: %Bone healed ranged from 16.17%( 4hr preop-18Gy)-40.87 %(Control). Controls showed statistical difference from right side (with collagen sponge) to left side (empty) only at 28 days of healing 40.87% vs.27.86%. Comparison of the radiographic imaging measurements and microCT data disclosed discrepancies in %healed between methods. Conclusions: Our results suggest Micro CT analysis of healing bony defects following radiation vary greatly from previous experiments using traditional 2D radiographic analysis. Although preliminary, these findings warrant further investigation into previous ideas of healing in irradiated bone and the rate it occurs. Further, these results suggest Micro CT is more accurate method of analysis because of the ability to measure volume in 3D as opposed to traditional 2D analysis.

Supported by a grant from the Oral and Maxillofacial Surgery Research and Education Fund (MGH/Harvard)

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