Background Our lab previously demonstrated that radiation significantly alters new bone formation in the murine mandible impeding the use of distraction osteogenesis (DO) as a viable reconstructive option after radiatiotherapy in Head and Neck Cancer (HNC). We hypothesize that the deleterious effects of radiation on regenerate formation results from a dose response (DR) depletion of essential osteogenic cells. Our specific aim is to use quantitative histomorphometry (QHM) to objectively measure the human equivalent DR effects of radiation on the integrity of the mandible’s cellular and tissue composition. Methods 20 Sprague-Dawley rats were randomIzed into three radiation dosage groups: low (5.91Gy), middle (7Gy) and high (8.89Gy) delivered in 5 daily fractions. These dosages approximated 75%, 100%, and 150% respectively of the bioequivalent dose the mandible experiences in the clinical regimen of HNC patients. Hemimandibles were harvested 56 days post-radiation, and stained with Gomori Trichrome. QHM was performed using Bioquant software and analysis with a one-way ANOVA Kruskal-Wallis test. Results Our data revealed a statistically significant diminution in the mean number of osteocytes . We also demonstrated a corresponding significant increase in the mean values of empty lacunae. Both of these QHM changes demonstrated a DR relationship. Conclusion Our study supports our hypothesis that radiation induces a DR depletion in osteocytes and an increase in empty lacunae. These reliable and reproducible metrics can now be utilized to determine the efficacy of therapies aimed at safeguarding the cells essential for optimal bone regeneration and potentially enhance the use of DO in HNC patients.

Background Head and neck cancer (HNC) management requires adjuvant radiation therapy (XRT). The authors have previously demonstrated the damaging effect of a human equivalent dose of radiation (HEDR) on a murine mandibular model of distraction osteogenesis (DO). Utilizing quantitative histomorphometry (QHM), our specific aim is to objectively measure the radio-protective effects of Amifostine (AMF) on the cellular integrity and tissue quality of an irradiated and distracted regenerate. Methods Sprague Dawley rats were randomly assigned into 2 groups: XRT/DO and AMF/XRT/DO, which received AMF prior to XRT. Both groups were given HEDR in 5 fractionated doses and underwent a left mandibular osteotomy with bilateral fixator placement. Distraction to 5.1mm was followed by a 28-day consolidation period. Left hemimandibles were harvested. QHM was performed for osteocyte count (Oc), empty lacunae (EL), Bone Volume/Tissue Volume (BV/TV) and Osteoid Volume/Tissue Volume (OV/TV) ratios. Results AMF/XRT/DO exhibited bony bridging as opposed to XRT/DO fibrous unions. QHM analysis revealed statistically significant higher Oc and BV/TV ratio in AMF-treated mandibles compared with irradiated mandibles. There was a corresponding decrease in EL and the ratio of OV/TV between AMF/XRT/DO and XRT/DO. Conclusion We have successfully established the significant osseous cytoprotective and histoprotective capacity of AMF on DO in the face of XRT. AMF-sparing effect on bone cellularity correlated with an increase in bony union and elimination of fibrous union. We posit that the demonstration of similar efficacy of AMF in the clinic may allow the successful implementation of DO as a viable reconstructive option for HNC in the future.